JP2016195143A - LED current control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED current control circuit that can detect current flowing in a bypass circuit and a constant current circuit by a simple current detecting resistor.SOLUTION: An LED current control circuit includes a current limiting circuit 102 for limiting LED current flowing between current limiting circuit terminals, a bypass circuit 101 for limiting bypass current flowing between the bypass circuit terminals which are connected between a first partial LED array 13 and a second partial LED array 14, and a current information detecting element 103 which is connected to the current limiting circuit output terminal and the bypass circuit output terminal. The current limiting circuit limits the LED current based on the current information detected by the current detecting element and the predictive coefficient. The bypass circuit limits the bypass current according to the state of a pulsating voltage based on the current information and a second coefficient different from the first coefficient, and control the current flowing from the first partial LED array through the bypass circuit to the current detection element so that the current flows to the second partial LED array without passing through the bypass circuit.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an LED (Light Emitting Diode) current control circuit. More specifically, the present invention relates to an LED current control circuit that controls a current flowing through an LED so that the number of lights to be turned on changes according to the voltage of a commercial AC power supply.

  There is known an LED drive circuit that applies a voltage having a waveform obtained by full-wave rectification of a voltage output from a commercial AC power supply to an LED array in which a plurality of LEDs are connected in series to light the LEDs. When a full-wave rectified voltage, also referred to as a pulsating voltage, is applied to the LED string, the LEDs are not lit at a phase lower than the total threshold voltage of the series-connected LED strings. The lighting device is dark and flickering. In order to reduce the time during which the LEDs do not emit light, a driving method is known in which the number of LEDs that are included in the LED array is turned on in accordance with the full-wave rectified voltage.

  For example, FIG. 26 of Patent Document 1 shows an LED lighting device 2600. The LED lighting device 2600 includes a commercial AC power supply, a bridge rectifier 2605, an LED array including LED groups 1 to 3, an FET Q1, a bypass circuit including a bipolar transistor Q2 and resistors R2 and R3, and a current limiting resistor R1. Prepare. Further, the bypass circuit of the LED lighting device 2600 is configured by a depletion type FET and a resistor, and the current limiting resistor R1 is replaced by a constant current circuit, thereby maintaining the same function as the LED lighting device 2600 and reducing the number of elements and operating the device. It is known to stabilize the system.

  FIG. 1 is a circuit block diagram of an example of a conventional LED lighting device.

  The LED lighting device 800 includes an LED drive circuit 80 and a commercial AC power source 82. The LED drive circuit 80 includes a bridge rectifier 81, a first partial LED string 83, a second partial LED string 84, a bypass circuit 801, and a current limiting circuit 802. The first partial LED string 83 and the second partial LED string 84 are connected in series to form an LED string. The bypass circuit 801 and the current limiting circuit 802 function as an LED current control circuit that controls the current flowing through the LED string.

  The bridge rectifier 81 has four diodes 81a, and a commercial AC power supply 82 is connected to the input terminal. The terminal E of the bridge rectifier 81 outputs a full-wave rectified voltage, and the current I is input from the bypass circuit 801 to the terminal F of the bridge rectifier 81. The first partial LED array 83 has a plurality of LEDs 83a connected in series, and the second partial LED array 84 has a plurality of LEDs 84a connected in series. The anode of the first stage LED 83 a of the first partial LED row 83 is connected to the terminal E, and the cathode of the last stage LED 83 a of the first partial LED row 83 is connected to the anode of the first stage LED 83 a of the second partial LED row 83. .

  The bypass circuit 801 includes a depletion type FET 85 and a resistor 87, and the drain of the FET 85 is connected to a connection portion that connects between the first partial LED row 83 and the second partial LED row 84. The source of the FET 85 is connected to the right terminal of the resistor 87, and the gate is connected to the left terminal of the resistor 87 and the terminal F. The current limiting circuit 802 includes a depletion type FET 86 and a resistor 88, and the drain of the FET 86 is connected to the cathode of the LED 84 a in the final stage of the second partial LED row 84. The source of the FET 86 is connected to the right terminal of the resistor 88, and the gate is connected to the left terminal of the resistor 88 and the source of the FET 85. The FET 85 and FET 86 are formed so that their electrical characteristics are equal to each other.

  2A shows one cycle of the voltage applied to the LED drive circuit 80, and FIG. 2B shows the magnitude of the current I that flows when the voltage shown in FIG. 2A is applied. It is.

  The current I does not flow during the period in which the applied voltage is equal to or lower than the threshold voltage of the first partial LED array 83. This period is indicated by t1 in FIG. In a period in which the applied voltage exceeds the threshold voltage of the first partial LED array 83 and does not reach the total voltage of the threshold voltage of the first partial LED array 83 and the threshold voltage of the second partial LED array 84, the first A current I flows from the one-part LED array 83 via the bypass circuit 801. At this time, the FET 85 operates at a constant current by feedback from the resistor 87 (hereinafter referred to as a first constant current operation state). This period is indicated by t2 in FIG. Further, when the applied voltage rises and exceeds the total voltage of the threshold voltage of the first partial LED array 83 and the threshold voltage of the second partial LED array 84, a current also flows through the second partial LED array 84. Become. At this time, the voltage drop of the resistor 87 becomes large, the FET 85 is turned off, and the FET 86 operates at a constant current by feedback from the resistor 88 (hereinafter referred to as a second constant current operation state). This period is indicated by t3 in FIG.

  According to the applied voltage, the LED drive circuit 80 includes a period in which the LEDs 83a and 84a are not lit at all, a period in which only the first partial LED row 83 is lit, and a first partial LED row 83 and a second partial LED row 84. Are both turned on.

  Further, by detecting the current flowing through the resistor connected to the source of the FET included in each of the current limiting circuit and the bypass circuit and controlling the current flowing through the FET, the luminous efficiency, power factor and total harmonics of the LED lighting device are controlled. It is known to improve distortion.

  FIG. 3 is an equivalent circuit block diagram of the conventional LED lighting device disclosed in Patent Document 2. As shown in FIG.

  The LED lighting device 900 includes an LED drive circuit 90 and a commercial AC power source 92. The LED drive circuit 90 includes a bridge rectifier 91, a first partial LED string 93, a second partial LED string 94, a bypass circuit 901, a current limiting circuit 902, a first current detection resistor 903, and a second current detection. And a resistor 904. Each of the first partial LED array 93 and the second partial LED array 94 includes a plurality of LEDs connected in series. The bypass circuit 901, the current limiting circuit 902, the first current detection resistor 903, and the second current detection resistor 904 function as an LED current control circuit that controls the current flowing through the LED array. The bridge rectifier 91, the commercial AC power source 92, the first partial LED row 93, and the second partial LED row 94 correspond to the bridge rectifier 81, the commercial AC power source 82, the first partial LED row 83, and the second partial LED row 84, respectively. It has a configuration.

  The bypass circuit 901 includes an FET 95 that is an enhanced FET, and a bypass circuit current control unit 970. The bypass circuit current control unit 970 includes a bypass circuit reference power supply 971 and a bypass circuit variable power supply 972. The negative terminal of the bypass circuit reference power supply 971 is connected to the source of the FET 95, the plus terminal of the bypass circuit reference power supply 971 is connected to the plus terminal of the bypass circuit variable power supply 972, and the minus terminal of the bypass circuit variable power supply 972 is connected to the gate of the FET 95. Connected. The gate-source voltage of the FET 95 is obtained by subtracting a voltage that is a constant multiple of the source voltage of the FET 95 (gain of the bypass circuit variable power source 972) from the voltage between both ends of the bypass circuit reference power source 971.

  In the bypass circuit variable power supply 972, when the current flowing through the first current detection resistor 903, that is, the drain current of the FET 95 increases, the voltage output to the gate of the FET 95 decreases. If the drain current of the FET 95 increases, the source voltage of the FET 95 (multiplied by a constant as described above) subtracted from the voltage of the bypass circuit reference power supply 971 increases, so the gate-source voltage of the FET 95 decreases and the drain current Try to reduce. Also, if the drain current of the FET 95 decreases, the source voltage of the FET 95 (multiplied by a constant as described above) subtracted from the voltage of the bypass circuit reference power supply 971 decreases, so that the gate-source voltage of the FET 95 rises and drains. Try to increase the current. That is, the bypass circuit 901 is negatively fed by the first current detection resistor 903 and the second current detection resistor 904. At this time, by setting the resistance values of the first current detection resistor 903 and the second current detection resistor 904 to appropriate values, the bypass circuit 901 can perform a constant current operation with a desired current.

  When the voltage output from the bridge rectifier 91 exceeds the total threshold voltage of the first partial LED string 93 and the second partial LED string 94 and a current flows into the second partial LED string, the gate-source voltage of the FET 95 is increased. The current flowing through the bypass circuit 901, that is, the current flowing through the FET 95 decreases.

  The current limiting circuit 902 includes an FET 96 that is an enhanced FET and a constant current circuit current control unit 980. The constant current circuit current control unit 980 includes a current limit circuit reference power source 981 and a current limit circuit variable power source 982. The negative terminal of the current limit circuit reference power supply 981 is connected to the source of the FET 96, the plus terminal of the current limit circuit reference power supply 981 is connected to the plus terminal of the current limit circuit variable power supply 982, and the minus terminal of the current limit circuit variable power supply 982 is Connected to the gate of FET 96. The voltage between the gate and source of the FET 96 is obtained by subtracting a voltage that is a constant multiple of the source voltage of the FET 96 (gain of the current limit circuit variable power source 982) from the voltage between both ends of the current limit circuit reference power source 981. The current limiting circuit 902 has a configuration similar to that of the bypass circuit 901.

  In the current limiting circuit 902, when the current flowing through the second current detection resistor 904, that is, the drain current of the FET 96 increases, the voltage output to the gate of the FET 96 decreases. If the drain current of the FET 96 increases, the source voltage of the FET 96 subtracted from the voltage of the current limit circuit reference power supply 981 (multiplied by a constant as described above) increases, so the gate-source voltage of the FET 96 decreases and the drain Try to reduce the current. If the drain current of the FET 96 decreases, the source voltage of the FET 96 subtracted from the voltage of the current limiting circuit reference power supply 981 (multiplied by a constant as described above) decreases, so that the gate-source voltage of the FET 96 increases. Try to increase the drain current. That is, the current limiting circuit 902 is negatively fed by the second current detection resistor 904. At this time, by setting the resistance value of the second current detection resistor 904 to an appropriate value, the current limiting circuit 902 can perform a constant current operation with a desired current.

  Further, by increasing the number of partial LED strings and the number of current detection resistors included in the LED string and connecting a plurality of bypass circuits having the same configuration as the bypass circuit 901 in parallel, luminous efficiency, power factor and total harmonics are increased. It becomes possible to provide an LED lighting device with even better distortion.

Special table 2013-502081 gazette International Publication No. 2013/100736

  However, the LED lighting device 900 has various problems caused by the first current detection resistor 903 and the second current detection resistor 904 being arranged to detect the current flowing through the bypass circuit 901 and the current limiting circuit 902, respectively. There is. For example, when the number of bypass circuits 901 is increased in order to improve the light emission efficiency and the like, the number of current detection resistors increases with an increase in the number of bypass circuits 901. When integrating the bypass circuit and current detection circuit, when using an external resistor as the current detection resistor to improve the accuracy of the resistance value of the current detection resistor, the number of terminals increases according to the number of current detection resistors. Will do. Further, as the number of current detection resistors increases, the power consumption consumed by the current detection resistors increases.

  Further, in the LED drive circuit 90, a second current detection resistor 904 that detects a current flowing in the current limiting circuit 902 located in the subsequent stage includes a first current detection resistor 903 that detects a current flowing in the bypass circuit 901 located in the preceding stage. Arranged between ground. In the LED drive circuit 90, since the second current detection resistor 904 is disposed between the first current detection resistor 903 and the ground, the bypass circuit 901, the current limiting circuit 902, the first current detection resistor 903, and the second current detection resistor The connection relationship 904 is complicated.

  Further, in the LED lighting device 900, a current flows through the first current detection resistor 903 via the bypass circuit 901 in order to define the voltage of the bypass circuit variable power source 972 while the current flows through the second partial LED array. ing. This current contributes to an increase in the amount of light emitted from the first partial LED array 93. However, since the voltage drop in the FET 95 is large, the power loss is large and the light emission efficiency of the LED lighting device 900 is reduced.

  An object of the present invention is to provide an LED current control circuit in which a bypass circuit and a constant current circuit are controlled based on a current detected by a single current detection resistor.

  To achieve the above object, an LED current control circuit according to the present invention includes a first partial LED string including a plurality of LEDs connected in series, and a first partial LED string including a plurality of LEDs connected in series. A current control circuit for controlling a current flowing in an LED array when a pulsating voltage is applied to the LED array including the second partial LED array connected in series, the current control circuit of the last stage LED of the second partial LED array A current limiting circuit including a current limiting circuit input terminal and a current limiting circuit output terminal connected to the cathode, and limiting a LED current flowing between the current limiting circuit input terminal and the current limiting circuit output terminal; a first partial LED array; A bypass circuit input terminal and a bypass circuit output terminal connected to a current limit circuit output terminal and a bypass circuit input terminal connected between the two partial LED strings, and a bypass circuit output terminal A bypass circuit that limits a bypass current flowing between the current detection circuit and a current detection element connected to the current limit circuit output terminal and the bypass circuit output terminal, wherein the current limit circuit includes current information detected by the current detection element and The LED current is limited based on a predetermined first coefficient, and the bypass circuit differs from the current information detected by the current detection element and the predetermined first coefficient according to the state of the pulsating voltage. The bypass current is limited based on the second coefficient so that the current that has flowed from the first partial LED string to the current detection element via the bypass circuit flows toward the second partial LED string without passing through the bypass circuit. It is characterized by controlling to.

  Furthermore, in the LED current control circuit according to the present invention, the current limiting circuit controls the first current limiting element using the first current limiting element that limits the magnitude of the LED current, and the current information and the first coefficient. A second current limiting element that limits the bypass current, and a second current controlling part that controls the second current limiting element using the current information and the second coefficient. It is preferable to have.

  Furthermore, in the LED current control circuit according to the present invention, each of the first current limiting element and the second current limiting element is an FET, and the first current control unit includes a first reference power supply, current information, a first coefficient, And a second variable current control unit that determines a voltage using a second reference power supply, current information, and a second coefficient. The gate-source voltage of the first current limiting element is obtained by subtracting the voltage of the first variable power supply from the voltage of the first reference power supply, and the gate-source voltage of the second current limiting element is: It is preferable that the voltage of the second variable power supply is subtracted from the voltage of the second reference power supply.

  Furthermore, in the LED current control circuit according to the present invention, it is preferable that the first coefficient and the second coefficient, and the voltages of the first reference power supply and the second reference power supply are each variable.

  Furthermore, in the LED current control circuit according to the present invention, the LED string includes a plurality of LEDs connected in series, and includes a third partial LED string connected in series between the first partial LED string and the second partial LED string. Further, a bypass circuit input terminal is connected between the first partial LED string and the third partial LED string, and is connected between the second partial LED string and the third partial LED string. A second bypass circuit output terminal connected to the current limit circuit output terminal and a second bypass circuit output terminal connected to the current limit circuit output terminal, the second bypass current flowing between the second bypass circuit terminal input terminal and the second bypass circuit terminal output terminal is limited; The second bypass circuit further includes current information detected by the current detection element according to a state of the pulsating voltage, and a first coefficient and a second coefficient that are different from the first coefficient and the second coefficient determined in advance. Based on 3 factors The second bypass current is limited so that the current flowing from the third partial LED string to the current detection element via the second bypass circuit flows toward the second partial LED string without passing through the second bypass circuit. It is preferable to control.

  According to the present invention, it is possible to provide an LED current control circuit in which a bypass circuit and a constant current circuit are controlled based on a current detected by a single current detection resistor.

It is a circuit block diagram of an example of the conventional LED lighting apparatus. (A) is a figure which shows 1 period of the voltage applied to the LED drive circuit shown in FIG. 1, (b) is a figure which shows the magnitude | size of the electric current which flows when the voltage shown in (a) is applied. is there. It is a circuit block diagram of the other example of the conventional LED lighting apparatus. It is a circuit block diagram of an example of an LED illuminating device. It is a circuit block diagram of the internal circuit of the LED lighting apparatus shown in FIG. It is a circuit block diagram of the other internal circuit of the LED lighting apparatus shown in FIG. (A) is a figure which shows the voltage-current characteristic of FET which the LED lighting apparatus shown in FIG. 4 has, (b) is a figure which shows the drain current of FET which the LED lighting apparatus shown in FIG. 4 has, (c ) Is a diagram showing the gate-source voltage of the FET included in the LED lighting device shown in FIG. It is a circuit block diagram of the other example of an LED lighting apparatus. (A) is a figure which shows the voltage-current characteristic of FET which the LED lighting apparatus shown in FIG. 8 has, (b) is a figure which shows the drain current of FET which the LED lighting apparatus shown in FIG. 8 has, (c FIG. 9 is a diagram illustrating a gate-source voltage of an FET included in the LED lighting device illustrated in FIG. 8. It is a circuit block diagram of the further another example of LED lighting apparatus. (A) is a figure which shows the voltage-current characteristic of FET which the LED lighting apparatus shown in FIG. 10 has, (b) is a figure which shows the drain current of FET which the LED lighting apparatus shown in FIG. FIG. 11 is a diagram illustrating a gate-source voltage of an FET included in the LED lighting device illustrated in FIG. 10. (A) is a figure which shows the relationship between the voltage-current characteristic of FET which the LED lighting apparatus shown in FIG. 10 has, and the voltage-current characteristic of a current control part, (b) is the elements on larger scale of (a). . (A) is a figure which shows the voltage-current characteristic of FET when the leakage current has arisen in the LED lighting apparatus shown in FIG. 10, (b) is a figure which shows the drain current of FET in the case of (a). (C) is a diagram showing the gate-source voltage of the FET in the case of (a). (A) is a figure which shows the relationship between the voltage-current characteristic of FET in the case of FIG. 13, and the voltage-current characteristic of a current control part, (b) is the elements on larger scale of (a). (A) is a figure which shows the voltage-current characteristic of FET when the leakage current has not arisen in the LED illuminating device shown in FIG. 10, (b) is a figure which shows the drain current of FET in the case of (a). (C) is a diagram showing the gate-source voltage of the FET in the case of (a). (A) is a figure which shows the relationship between the voltage-current characteristic of FET in the case of FIG. 15, and the voltage-current characteristic of a current control part, (b) is the elements on larger scale of (a). It is a circuit block diagram of the further another example of LED lighting apparatus. (A) is a figure which shows the voltage-current characteristic of FET which the LED lighting apparatus shown in FIG. 17 has, (b) is a figure which shows the drain current of FET which the LED lighting apparatus shown in FIG. FIG. 18 is a diagram illustrating a gate-source voltage of an FET included in the LED lighting device illustrated in FIG. 17. (A) is a figure which shows the relationship between the voltage-current characteristic of FET which the LED lighting apparatus shown in FIG. 17 has, and the voltage-current characteristic of a current control part, (b) is the elements on larger scale of (a). . (A) is a circuit block diagram of an example of an LED lighting device having two semiconductor devices connected in series, and (b) is a circuit block of another example of an LED lighting device having two semiconductor devices connected in series. FIG. 6C is a circuit block diagram of still another example of an LED lighting device having two semiconductor devices connected in series. (A) is a figure which shows the drain current of FET of the LED lighting apparatus shown to Fig.20 (a), (b) is a figure which shows the drain current of FET of the LED lighting apparatus shown in FIG.20 (b), (C) is a figure which shows the drain current of FET of the LED lighting apparatus shown in FIG.20 (c). (A) is a circuit block diagram of an example of an LED lighting device having two semiconductor devices connected in parallel, (b) is a circuit block of another example of an LED lighting device having two semiconductor devices connected in parallel FIG. (A) is a figure which shows the drain current of FET of the LED lighting apparatus shown to Fig.22 (a), (b) is a figure which shows the drain current of FET of the LED lighting apparatus shown in FIG.22 (b).

  Hereinafter, an LED lighting device, an LED drive circuit, and an LED current control circuit according to the present invention will be described with reference to the drawings. However, it should be noted that the technical scope of the present invention is not limited to these embodiments, and extends to equivalents to the invention described in the claims.

  FIG. 4 is a circuit block diagram of the LED lighting device according to the first embodiment.

  The LED lighting device 100 includes an LED drive circuit 10 and a commercial AC power supply 12. The LED drive circuit 10 includes a bridge rectifier 11, a first partial LED string 13, a second partial LED string 14, a bypass circuit 101, a current limiting circuit 102, and a current detection resistor 103. Each of the first partial LED row 13 and the second partial LED row 14 has a plurality of LEDs connected in series. The bypass circuit 101, the current limiting circuit 102, and the current detection resistor 103 function as an LED current control circuit that controls the current flowing through the LED string. The bridge rectifier 11, the commercial AC power source 12, the first partial LED row 13 and the second partial LED row 14 correspond to the bridge rectifier 81, the commercial AC power source 82, the first partial LED row 83 and the second partial LED row 84, respectively. It has a configuration. The bypass circuit 101 includes an FET 15 that is an enhanced FET and a bypass circuit current control unit 170. The drain of the FET 15 is a bypass current input terminal connected between the first partial LED string 13 and the second partial LED string 14, and the source of the FET 15 is a bypass current output connected to one terminal of the current detection resistor 103. Terminal. The current limiting circuit 102 includes an FET 16 that is an enhanced FET and a current limiting circuit current control unit 180. The drain of the FET 16 is a limiting current input terminal connected to the cathode of the LED in the final stage of the second partial LED row 14, and the source of the FET 16 is a limiting current output terminal connected to one terminal of the current detection resistor 103. .

  FIG. 5 is a circuit block diagram of an internal circuit of the bypass circuit current control unit 170.

The bypass circuit current control unit 170 includes a bypass circuit reference power supply 171 and a bypass circuit variable power supply 172. Bypass circuit reference power 171 includes an operational amplifier 1710, and the 11 resistance 1711 resistance value of R _11, the resistance value of the 12th resistor 1712 is R _12. The twelfth resistor 1712 is a variable resistor. A voltage of 1V is input to the positive input terminal of the operational amplifier 1710, and from the output terminal of the operational amplifier 1710,
V _ref = (1+ (R ₁₂ / R ₁₁ )) × 1V
Is output.

The bypass circuit variable power source 172 includes an amplifying unit 173, a first subtracting unit 174, and a second subtracting unit 175. Amplifying unit 173 includes an operational amplifier 1730, and the 31 resistance 1731 resistance value is R _31, the resistance value of the first 72 resistor 1732 is R _72. The 72nd resistor 1732 is a variable resistor. The voltage V _sen between the terminals of the current detection resistor 103 is input to the positive input terminal of the operational amplifier 1730. From the output terminal of the operational amplifier 1730,
V _sen1 = (1+ (R ₇₂ / R ₃₁ )) × V _sen
Is output. Here, if 1+ (R ₇₂ / R ₃₁ ) is the bypass circuit gain g _b ,
V _sen1 = g _b × V _sen
It becomes.

First subtraction unit 174, an operational amplifier 1740, and the 41 resistance 1741 resistance value is R _41, and the 42 resistance 1742 resistance value is R _42, and the 43 resistance 1743 resistance value is R _43, resistance and a 44th resistor 1744 is R _44. From the output terminal of the operational amplifier 1740,
V _40out = (1+ (R ₄₄ / R ₄₃ )) ×
((R ₄₂ / (R ₄₁ + R ₄₂ )) V _sen1 − (R ₄₄ / (R ₄₃ + R ₄₄ )) V _sen )
Is output. Here, by making all the resistance values R ₄₁ , R ₄₂ , R ₄₃ and R ₄₄ of the 41st resistor 1741, the 42nd resistor 1742, the 43rd resistor 1743 and the 44th resistor 1744 equal,
_V 40out = V sen1 -V _sen
It can be.

The second subtracting unit 175, an operational amplifier 1750, and the 51 resistance 1751 resistance value is R _51, and the 52 resistance 1752 resistance value is R _52, and the 53 resistance 1753 resistance value is R _53, resistance and a 54th resistor 1754 is R _54. From the output terminal of the operational amplifier 1750,
V _50out = (1+ (R ₅₄ / R ₅₃ )) ×
[(R ₅₂ / (R ₅₁ + R ₅₂ )) V _ref − (R ₅₄ / (R ₅₃ + R ₅₄ )) V _40out ]
Is output. Here, by making the resistance values R ₅₁ , R ₅₂ , R ₅₃ and R ₅₄ of the 51st resistor 1751, the 52nd resistor 1752, the 53rd resistor 1753 and the 54th resistor 1754 all equal,
_V 50out = V _ref -V 40out
_{= V ref - (V sen1 -V} sen) = (V ref -V sen1) + V sen
It can be. Here, V _50out is the gate voltage Vg of the FET 15. The source voltage Vs of the FET15 is a terminal voltage V _sen of the current detection resistor 103. Therefore, the gate-source voltage Vgs of the FET 15 is
Vgs = Vg−Vs
= V _50out -V _sen
= (V _ref −V _sen1 ) + V _sen −V _sen
= V _ref -V _sen1
= V _ref -g _b × V _sen
It becomes.

  FIG. 6 is a circuit block diagram of an internal circuit of the current limiting circuit current control unit 180.

The current limit circuit current control unit 180 includes a current limit circuit reference power source 181 and a current limit circuit variable power source 182. The current limit circuit reference power supply 181 has the same configuration as the bypass circuit reference power supply 171, and, similar to the operational amplifier 1710, from the output terminal of the operational amplifier 1810,
V _ref = (1+ (R ₁₂ / R ₁₁ )) × 1V
Is output.

  The current limiting circuit variable power source 182 includes an amplifying unit 183, a first subtracting unit 184, and a second subtracting unit 185. The first subtraction unit 184 has the same configuration as the first subtraction unit 174 of the bypass circuit variable power supply 172, and the second subtraction unit 185 has the same configuration as the second subtraction unit 175 of the bypass circuit variable power supply 172. .

Amplifying unit 183 includes an operational amplifier 1830, and the 31 resistance 1831 resistance value is R _31, the resistance value of the first 82 resistor 1832 is R _82. The 82nd resistor 1832 is a variable resistor. The voltage V _sen between the terminals of the current detection resistor 103 is input to the positive input terminal of the operational amplifier 1830. From the output terminal of the operational amplifier 1830,
V _sen2 = (1+ (R ₈₂ / R ₃₁ )) × V _sen
Is output. Here, if 1+ (R ₈₂ / R ₃₁ ) is the current limiting circuit gain g _c ,
V _sen2 = g _c × V _sen
It becomes. Therefore, the gate-source voltage Vgs of the FET 16 is
Vgs = Vg−Vs
= V _50out -V _sen
= (V _ref -V _sen2 ) + V _sen -V _sen
= V _ref -V _sen2
= V _ref -g _c × V _sen
It becomes.

  The amplifying unit 173 of the bypass circuit variable power source 172 and the amplifying unit 183 of the current limiting circuit variable power source 182 have different gains by making the resistance value of the 72nd resistor 1732 and the resistance value of the 82nd resistor 1832 different. I am letting.

  FIG. 7A is a diagram illustrating the relationship between the Vgs-Id curves of the FETs 15 and 16 and the voltages generated by the amplification units 173 and 183. FIG. 7B is a diagram showing a change with time of the drain current Id of the FET 15, the drain current Id of the FET 16, and the total value of the drain currents Id of the FETs 15 and 16. FIG. 7C is a diagram showing the change over time of the gate-source voltage Vgs of the FET 15 and the gate-source voltage Vgs of the FET 16. In FIG. 7A, the horizontal axis indicates the gate-source voltage Vgs of the FETs 15 and 16, and the vertical axis indicates the drain current Id of the FETs 15 and 16. In FIG. 7B, the horizontal axis represents the time for one cycle of the full-wave rectified waveform, and the vertical axis represents the drain current Id of the FETs 15 and 16. In FIG. 7B, the solid line indicates the drain current Id of the FET 15, the broken line indicates the drain current Id of the FET 16, and the alternate long and short dash line indicates the total current of the drain currents of the FETs 15 and 16. 7C, the horizontal axis indicates the time corresponding to the horizontal axis in FIG. 7B, and the vertical axis indicates the gate-source voltage Vgs of the FETs 15 and 16. In FIG. 7C, the solid line indicates the gate-source voltage Vgs of the FET 15, and the broken line indicates the gate-source voltage Vgs of the FET 16. In FIG. 7C, the applied voltage is equal to or lower than the threshold voltage of the first partial LED array 13 during the period indicated by t1, and a current flows through both the first partial LED array 13 and the second partial LED array 14. It is not a period. Further, during the period indicated by t2, the applied voltage is larger than the threshold voltage of the first partial LED array 13, and the total voltage of the threshold voltage of the first partial LED array 13 and the threshold voltage of the second partial LED array 14 This is a period during which current flows through the first partial LED array 13. In the period indicated by t3, the applied voltage becomes larger than the total voltage of the threshold voltage of the first partial LED string 13 and the threshold voltage of the second partial LED string 14, and the first partial LED string 13 and the first partial LED string 13 This is a period during which current flows through both of the two partial LED strings 14.

In the period t1 shown in FIG. 7C, since no current flows through both the first partial LED array 13 and the second partial LED array 14, no current flows through the current detection resistor 103. As no current flows through the current detection resistor 103, the gate-source voltage Vgs of the FETs 15 and 16 becomes V _ref as shown in FIG. 7C.

In the period t2 shown in FIG. 7C, current flows through the first partial LED array 13 and no current flows through the second partial LED array 14. _Assuming that the potential difference generated in the current detection resistor 103 in the period t2 is V _{sen_t2} , the gate-source voltage Vgs of the FET ₁₅ is V _ref −g _b × V _{sen_t2} , and the gate-source voltage Vgs of the FET 16 is V _ref −g _c × V _{sen_t2.} It becomes. V _ref −g _b × V _{sen — t2,} which is the gate-source voltage Vgs of the FET 15, is equal to Vgs ₁ in FIGS. 7A and 7C.

In a period t3 shown in FIG. 7C, a current flows through both the first partial LED array 13 and the second partial LED array 14. If the potential difference generated in the current detection resistor 103 in the period t3 is V _{sen_t3} , the gate-source voltage Vgs of the FET ₁₅ is V _ref −g _b × V _{sen_t3} , and the gate-source voltage Vgs of the FET 16 is V _ref −g _c × V _{sen_t3.} It becomes. V _ref −g _c × V _{sen — t3} which is the gate-source voltage Vgs of the FET 16 is equal to Vgs2 in FIGS. 7A and 7C. Further, since V _ref −g _b × V _{sen —} t3 which is the gate-source voltage Vgs of the _{FET 15} is smaller than the threshold voltage of the FET 15, no current flows through the bypass circuit 101 in the period t3. The bypass circuit 101 controls the current flowing through the current detection resistor 103 through the bypass circuit 101 in the period t2 to flow toward the second partial LED array 14 in the period t3.

  FIG. 8 is a circuit block diagram of the LED lighting device according to the second embodiment.

  The LED lighting device 200 includes an LED drive circuit 20 and a commercial AC power supply 22. The LED drive circuit 20 includes a bridge rectifier 21, a first partial LED string 23, a second partial LED string 24, a bypass circuit 201, a current limiting circuit 202, and a current detection resistor 203. Each of the first partial LED array 23 and the second partial LED array 24 has a plurality of LEDs connected in series. The bypass circuit 201, the current limiting circuit 202, and the current detection resistor 203 function as an LED current control circuit that controls the current flowing through the LED string. The bridge rectifier 21, the commercial AC power source 22, the first partial LED row 23, and the second partial LED row 24 correspond to the bridge rectifier 81, the commercial AC power source 82, the first partial LED row 83, and the second partial LED row 84, respectively. It has a configuration. The bypass circuit 201 includes an FET 25 that is a depletion type FET and a bypass circuit current control unit 270. The current limiting circuit 202 includes a FET 26 that is a depletion type FET, and a current limiting circuit current control unit 280.

  The bypass circuit current control unit 270 is different from the bypass circuit current control unit 170 in that it has only a bypass circuit variable power source 272 corresponding to the bypass circuit variable power source 172 without having a configuration corresponding to the bypass circuit reference power source 171. . In addition, the current limit circuit current control unit 280 does not have a configuration corresponding to the current limit circuit reference power source 181, but includes only the current limit circuit variable power source 282 corresponding to the current limit circuit variable power source 182. This is different from the current control unit 180. Since the threshold voltages of the FETs 25 and 26 arranged in the bypass circuit current control unit 270 and the current limiting circuit current control unit 280 are sufficiently smaller than 0V, the gate voltage does not need to be raised, so the reference power supply is not arranged. .

  FIG. 9A is a diagram illustrating the relationship between the Vgs-Id curves of the FETs 25 and 26 and the voltages generated by the amplification units 273 and 283. FIG. 9B is a diagram showing temporal changes in the drain current Id of the FET 25, the drain current Id of the FET 26, and the total value of the drain currents Id of the FETs 25 and 26. FIG. 9C is a diagram showing temporal changes in the absolute values of the gate-source voltage Vgs of the FET 25, the gate-source voltage Vgs of the FET 26, and the terminal voltage of the current detection resistor 203. In FIG. 9A, the horizontal axis represents the gate-source voltage Vgs of the FETs 25 and 26, and the vertical axis represents the drain current Id of the FETs 25 and 26. In FIG. 9B, the horizontal axis represents the time for one cycle of the full-wave rectified waveform, and the vertical axis represents the drain current Id of the FETs 25 and 26. In FIG. 9B, the solid line indicates the drain current Id of the FET 25, the broken line indicates the drain current Id of the FET 26, and the alternate long and short dash line indicates the total current of the drain currents of the FETs 25 and 26. 9C, the horizontal axis indicates the time corresponding to the horizontal axis in FIG. 7B, and the vertical axis indicates the gate-source voltage Vgs (absolute value) of the FETs 25 and 26. In FIG. 9C, the solid line indicates the absolute value of the gate-source voltage Vgs of the FET 25, the broken line indicates the absolute value of the gate-source voltage Vgs of the FET 26, and the alternate long and short dash line indicates the voltage between the terminals of the current detection resistor 203. . In FIG. 9C, the applied voltage is equal to or lower than the threshold voltage of the first partial LED row 23 during the period indicated by t1, and current flows through both the first partial LED row 23 and the second partial LED row 24. It is not a period. Further, during the period indicated by t2, the applied voltage is larger than the threshold voltage of the first partial LED array 23, and the total voltage of the threshold voltage of the first partial LED array 23 and the threshold voltage of the second partial LED array 24 This is a period during which current flows through the first partial LED array 23. In the period indicated by t3, the applied voltage becomes larger than the total voltage of the threshold voltage of the first partial LED array 23 and the threshold voltage of the second partial LED array 24, and the first partial LED array 23 and the first partial LED array 23 This is a period during which current flows through both of the two partial LED strings 24.

  In the period t1 shown in FIG. 9C, no current flows through both the first partial LED array 23 and the second partial LED array 24, and therefore no current flows through the current detection resistor 203. As no current flows through the current detection resistor 103, the gate-source voltage Vgs of the FETs 15 and 16 is 0V as shown in FIG. 7C.

In a period t <b> 2 shown in FIG. 9C, current flows through the first partial LED array 23 and no current flows through the second partial LED array 24. If the potential difference generated in the current detection resistor 203 in the period t2 is V _{sen_t2} , the gate-source voltage Vgs of the FET 25 is −g _b × V _{sen_t2} , and the gate-source voltage Vgs of the _{FET 26} is −g _c × V _{sen_t2} . The magnitude of −g _b × V _{sen — t2} which is the gate-source voltage Vgs of the FET 15 is equal to Vgs1 in FIGS. 9A and 9C (shown as an absolute value in FIG. 9).

In a period t3 shown in FIG. 9C, a current flows through both the first partial LED row 23 and the second partial LED row 24. When the potential difference generated in the current detection resistor 203 in the period t3 is V _{sen_t3} , the gate-source voltage Vgs of the FET 25 is −g _b × V _{sen_t3} , and the gate-source voltage Vgs of the _{FET 26} is −g _c × V _{sen_t3} . −g _c × V _{sen — t3,} which is the gate-source voltage Vgs of the _{FET 26,} is equal to Vgs2 in FIGS. 9A and 9C (shown as an absolute value in FIG. 9). In addition, since −g _b × V _{sen —} t3, which is the gate-source voltage Vgs of the FET 25, is smaller than the threshold voltage of the FET 25, no current flows through the bypass circuit 201 during the period t 3. The bypass circuit 201 controls the current flowing through the current detection resistor 203 via the bypass circuit 201 to flow toward the second partial LED array 14 in the period t2.

  FIG. 10 is a circuit block diagram of the LED lighting device according to the third embodiment.

  The LED illumination device 110 includes an LED drive circuit 111 and a commercial AC power supply 12. The LED drive circuit 111 is different from the LED drive circuit 10 in that it includes a first bypass circuit 101a and a second bypass circuit 101b having a configuration corresponding to the bypass circuit 101. The LED lighting device 110 is different from the LED 100 in that the LED row is divided into a first partial LED row 13a, a second partial LED row 13b, and a third partial LED row 14.

The first bypass circuit 101a includes an FET 15a, which is an enhanced FET, and a first bypass circuit current control unit 170a. The first bypass circuit current control unit 170a includes a first bypass circuit reference power source 171a and a first bypass circuit variable power source 172a. The gain of the first bypass circuit variable power source 172a is g _b1 . The first bypass circuit 101a controls the current flowing through the current detection resistor 103 via the first bypass circuit 101a to flow toward the second partial LED row 13b according to the state of the pulsating voltage.

The second bypass circuit 101b includes an FET 15b, which is an enhanced FET, and a second bypass circuit current control unit 170b. The second bypass circuit current control unit 170b includes a second bypass circuit reference power source 171b and a second bypass circuit variable power source 172b. Gain of the second bypass circuit variable power source 172b is g _b2. The second bypass circuit 101b controls the current flowing through the current detection resistor 103 via the second bypass circuit 101b to flow toward the third partial LED array 14 according to the state of the pulsating voltage.

  FIG. 11A is a diagram illustrating the relationship between the Vgs-Id curves of the FETs 15a, 15b, and 16, and the voltages generated by the amplifiers 173a, 173b, and 183. FIG. 11B is a diagram showing a change with time of the drain current Id of the FET 15a, the drain current Id of the FET 15b, the drain current Id of the FET 16, and the total values of the drain currents Id of the FETs 15a, 15b and 16. FIG. 11C is a diagram showing the change over time of the gate-source voltage Vgs of the FETs 15a, 15b and 16. 11A to 11C correspond to the vertical axis and the horizontal axis of FIGS. 7A to 7C, respectively. In FIG. 11B, the solid line indicates the drain current Id of the FET 15a, the broken line indicates the drain current Id of the FET 15b, and the alternate long and short dash line indicates the drain current Id of the FET 16. The two-dot chain line indicates the total current of the drain currents of the FETs 15a, 15b and 16. In FIG. 11C, the solid line indicates the gate-source voltage Vgs of the FET 15a, the broken line indicates the gate-source voltage Vgs of the FET 15b, and the alternate long and short dash line indicates the gate-source voltage Vgs of the FET 16. In FIG. 11C, a period indicated by t1 is a period in which no current flows through all of the first partial LED string 13a, the second partial LED string 13b, and the third partial LED string 14. The period indicated by t2 is a period in which current flows only in the first partial LED row 13a. Moreover, the period shown by t3 is a period when the electric current is flowing into the 1st partial LED row 13a and the 2nd partial LED row 13b. The period indicated by t4 is a period in which current flows through all of the first partial LED row 13a, the second partial LED row 13b, and the third partial LED row 14.

In the period t1 shown in FIG. 11C, since no current flows through all of the first partial LED array 13a, the second partial LED array 13b, and the third partial LED array 14, current also flows through the current detection resistor 103. Absent. No current flows through the current detection resistor 103, and the gate-source voltages Vgs of the FETs 15a, 15b, and 16 are all V _ref as shown in FIG. 11C.

In the period t2 shown in FIG. 11C, current flows only through the first partial LED row 13a. If the potential difference generated in the current detection resistor 103 in the period t2 is V _{sen_t2} , the gate-source voltage Vgs of the FET 15a is V _ref −g _b1 × V _{sen_t2} , and the gate-source voltage Vgs of the _{FET 15b} is V _ref −g _b2 × V _{sen_t2.} It becomes. The gate-source voltage Vgs of the FET 16 is V _ref −g _c × V _{sen — t 2} . V _ref −g _b1 × V _{sen — t2} that is the gate-source voltage Vgs of the FET 15a is equal to _Vgs1a in FIGS. 11 (a) and 11 (c).

In a period t3 shown in FIG. 11C, a current flows through the first partial LED row 13a and the second partial LED row 13b. If the potential difference generated in the current detection resistor 103 in the period t3 is V _{sen_t3} , the gate-source voltage Vgs of the FET 15a is V _ref −g _b1 × V _{sen_t3} , and the gate source voltage Vgs of the _{FET 15b} is V _ref −g _b2 × V _{sen_t3.} It becomes. The gate-source voltage Vgs of the FET 16 is V _ref −g _c × V _{sen — t3} . V _ref −g _b2 × V _{sen — t2,} which is the gate-source voltage Vgs of the FET 15b, is equal to _Vgs1b in FIGS. 11 (a) and 11 (c).

In the period t4 shown in FIG. 11C, a current flows through all of the first partial LED row 13a, the second partial LED row 13b, and the third partial LED row 14. If the potential difference generated in the current detection resistor 103 in the period t4 is V _{sen_t4} , the gate-source voltage Vgs of the FET 15a is V _ref −g _b1 × V _{sen_t4} , and the gate-source voltage Vgs of the _{FET 15b} is V _ref −g _b2 × V _{sen_t4.} It becomes. Further, the gate-source voltage Vgs of the FET 16 is V _ref −g _c × V _{sen — t 4} . V _ref −g _c × V _{sen — t4,} which is the gate-source voltage Vgs of the FET 16, is equal to Vgs ₂ in FIGS. 11A and 11C.

  FIG. 12A is a diagram showing the relationship between the voltage-current characteristics of the FETs 15a, 15b, and 16, and the voltage-current characteristics of the current control units of the first bypass circuit 101a, the second bypass circuit 101b, and the current limiting circuit 102. It is. FIG.12 (b) is the elements on larger scale of the figure shown to Fig.12 (a). 12A and 12B, the horizontal axis indicates the gate-source voltage Vgs of the FETs 15a, 15b, and 16, and the vertical axis indicates the drain current of the FETs 15a, 15b, and 16. In each of FIGS. 12A and 12B, the solid lines indicate the voltage-current characteristics of the FETs 15a, 15b, and 16, and the broken lines indicate the voltage-current characteristics of the first bypass circuit current control unit 170a. The alternate long and short dash line indicates the voltage-current characteristic of the second bypass circuit current control unit 170b, and the alternate long and two short dashes line indicates the voltage-current characteristic of the current limiting circuit current control unit 180. The voltage of the first bypass circuit 101a, the second bypass circuit 101b, or the current limiting circuit 102 is the FET 15a, 15b when the first bypass circuit 101a, the second bypass circuit 101b, or the current limiting circuit 102 is operating independently. , 16 corresponding to the gate-source voltage Vgs. The currents of the first, second, and third bypass circuit current control units are the drain currents of the FETs 15a, 15b, and 16 when the first bypass circuit 101a, the second bypass circuit 101b, or the current limiting circuit 102 is operating independently. It corresponds to Id.

The voltage-current characteristic of the first bypass circuit current control unit 170a is that the gate voltage Vg of the FET 15a is
_{Vg = V ref + V sen -g} b1 × R s × Ids
The source voltage Vs of the FET 15a is
Vs = V _sen
Therefore, when expressed by Vgs and Ids,
_{Vgs = V ref -g b1 × R} s × Ids
It becomes the relationship. Similarly, the voltage-current characteristic of the second bypass circuit current control unit 170b indicates that the gate voltage Vg of the FET 15b is
_{Vg = V ref + V sen -g} b2 × R s × Ids
The source voltage Vs of the FET 15a is
Vs = V _sen
Therefore, when expressed by Vgs and Ids,
_{Vgs = V ref -g b2 × R} s × Ids
It becomes the relationship. Similarly, the voltage-current characteristic of the current limiting circuit current control unit 180 is that the gate voltage Vg of the FET 15b is
_{Vg = V ref + V sen -g} c × R s × Ids
The source voltage Vs of the FET 15a is
Vs = V _sen
Therefore, when expressed by Vgs and Ids,
_{Vgs = V ref -g c × R} s × Ids
It becomes the relationship. Here, R _s is the resistance value of the current detection resistor 103. The intersection of the voltage-current characteristic line of the first bypass circuit current control unit 170a, the second bypass circuit current control unit 170b and the current limiting circuit current control unit 180 and the voltage-current characteristic curve of the FET voltage-current characteristic is the operation of the FET. It becomes a point. That is, if the voltage V _{ref of the} bypass circuit reference power source 171a and the like and the resistance value R _s of the current detection resistor 103 are given, the gains of the first bypass circuit variable power source 172a, the second bypass circuit variable power source 172b, and the current limit circuit variable power source 182 By determining g _b1 , g _b2, and g _c , the current that flows through the first partial LED row 13a, the second LED 13b, and the third partial LED row 14 is determined.

If the voltage V _ref and the gains g _b1 , g _b2 , and g _c are appropriately set, the first bypass circuit 101a is cut off when the second bypass circuit 101b is operating at a constant current. Similarly, when the current limiting circuit 102 operates at a constant current, the first and second bypass circuits 101a and 101b are cut off. However, if the voltage V _ref and the gains g _b1 , g _b2 , and g _c are set inappropriately, for example, a leakage current may be generated in the second bypass circuit 101b when the current limiting circuit 102 is operating at a constant current. is there. Therefore, a leakage current preventing function in the LED lighting device 110 will be described with reference to FIGS.

  13 and 14 are diagrams illustrating electrical characteristics when a leakage current is generated in the LED lighting device 110, and FIGS. 15 and 16 are diagrams illustrating electrical characteristics when no leakage current is generated in the LED lighting device 110. is there. 13 and 15 correspond to FIG. 11, and FIGS. 14 and 16 correspond to FIG.

13 to 16, an AC voltage having an amplitude of 120V is applied to the commercial AC power supply 12, the threshold voltages of the FETs 15a, 15b, and 16 are 3.8V, and the resistance value of the current detection resistor 103 is 1Ω. 13 and 14, the voltages of the first bypass circuit reference power source 171a, the second bypass circuit reference power source 171b, and the current limiting circuit reference power source 181 are 4.1V. The gain g _b1 of the first bypass circuit variable power source 172a is 3.4, the gain g _b2 of the second bypass circuit variable power source 172b is 2.5, and the gain g _c of the current limit circuit variable power source 182 is 2. .0. On the other hand, in FIGS. 15 and 16, the voltages of the first bypass circuit reference power supply 171a, the second bypass circuit reference power supply 171b, and the current limiting circuit reference power supply 181 are 8.0V. The gain g _b1 of the first bypass circuit variable power source 172a is 59.1, the gain g _b2 of the second bypass circuit variable power source 172b is 45.9, and the gain g _c of the current limit circuit variable power source 182 is 37. .5.

In the period t2 in FIG. 13C, a current of 70 mA flows in the FET 15a and no current flows in the FETs 15b and 16, so the total current becomes 70 mA. In the period t3 in FIG. 13C, a current of 91 mA flows through the FET 15b and no current flows through the FETs 15a and 16, so the total current is 91 mA. However, in the case of this condition, since the gain g _{c and the} like are improperly set as described above, a leakage current is generated in the bypass circuit 101b in the period t4 in FIG. At this time, although the total current is 112 mA, the current flowing through the FET 16 is 104 mA, and a current of 8 mA flows through the FET 15 b. When the voltage V _{ref of} the second bypass circuit reference power source 171b is 4.1 and the gain g _{b2 of} the second bypass circuit variable power source 172b is 2.5, the current flowing through the current detection resistor 103 is 112 mA. ,
_{Vgs = V ref -g b2 × V} sen_t4
= 4.1V-2.5 × 122mA × 1Ω
= 3.82V
It becomes. For this reason, as shown in FIG. 14B, a leakage current of 8 mA flows through the FET 16b. Therefore, the voltages of the first bypass circuit reference power supply 171a, the second bypass circuit reference power supply 171b and the current limiting circuit reference power supply 181 and the gains of the first bypass circuit variable power supply 172a and the second bypass circuit variable power supply 172b are changed, Set the leakage current to zero.

In the period t2 in FIG. 15C, a current of 70 mA flows through the FET 15a and no current flows through the FETs 15b and 16, so the total current becomes 70 mA. In the period t3 in FIG. 15C, a current of 90 mA flows through the FET 15b and no current flows through the FETs 15a and 16, so the total current becomes 90 mA. In the period t4 in FIG. 15C, a current of 110 mA flows through the FET 16 and no current flows through the FETs 15a and 15b, so the total current becomes 110 mA. When the voltage V _{ref of} the second bypass circuit reference power source 171b is 8.0 and the gain g _{b2 of} the second bypass circuit variable power source 172b is 45.9, the current flowing through the current detection resistor 103 is 110 mA. ,
_{Vgs = V ref -g b2 × V} sen_t4
= 8.0V-45.9 × 110mA × 1Ω
= 2.951V
Thus, the threshold voltage of the FET 15b is lower than 3.8V.

  FIG. 17 is a circuit block diagram of the LED lighting device according to the fourth embodiment.

  The LED lighting device 210 includes an LED drive circuit 211 and a commercial AC power supply 22. The LED drive circuit 211 is different from the LED drive circuit 20 in that it includes a first bypass circuit 201a and a second bypass circuit 201b having a configuration corresponding to the bypass circuit 201. The LED lighting device 210 is different from the LED lighting device 200 in that the LED row is divided into a first partial LED row 23a, a second partial LED row 23b, and a third partial LED row 24.

The first bypass circuit 201a includes an FET 25a that is a depletion type FET, and a first bypass circuit current control unit 270a. The first bypass circuit current control unit 270a includes a first bypass circuit variable power supply 272a gain is g _b1.

The second bypass circuit 201b includes an FET 25b that is a depletion type FET, and a second bypass circuit current control unit 270b. The second bypass circuit current control unit 270b includes a second bypass circuit variable power source 272b gain is g _b2.

  FIG. 18A is a diagram illustrating a relationship between the Vgs-Id curves of the FETs 25a, 25b, and 26 and the voltages generated by the amplification units 273a, 273b, and 283. FIG. 18B is a diagram showing temporal changes in the drain current Id of the FET 25a, the drain current Id of the FET 25b, the drain current Id of the FET 26, and the total values of the drain currents Id of the FETs 25a, 25b and 16. FIG. 18C is a diagram showing the change over time of the gate-source voltage Vgs (absolute value) of the FETs 25a, 25b and 26. FIG. The vertical and horizontal axes in FIGS. 18A to 18C correspond to the vertical and horizontal axes in FIGS. 9A to 9C, respectively. In FIG. 18B, the solid line indicates the drain current Id of the FET 25a, the broken line indicates the drain current Id of the FET 25b, and the alternate long and short dash line indicates the drain current Id of the FET 26. The two-dot chain line indicates the total current of the drain currents of the FETs 25a, 25b and 26. In FIG. 18C, the solid line indicates the gate-source voltage Vgs of the FET 25a, the broken line indicates the gate-source voltage Vgs of the FET 25b, and the alternate long and short dash line indicates the gate-source voltage Vgs of the FET 26. In FIG. 18C, a period indicated by t1 is a period in which no current flows through all of the first partial LED row 23a, the second partial LED row 23b, and the third partial LED row 24. The period indicated by t2 is a period in which current flows only in the first partial LED row 23a. The period indicated by t3 is a period in which current flows through the first partial LED row 23a and the second partial LED row 23b. The period indicated by t4 is a period during which current flows through all of the first partial LED row 23a, the second partial LED row 23b, and the third partial LED row 24.

  In the period t1 shown in FIG. 18C, since no current flows through all of the first partial LED row 23a, the second partial LED row 23b, and the third partial LED row 24, current also flows through the current detection resistor 203. Absent. As no current flows through the current detection resistor 203, the gate-source voltages Vgs of the FETs 25a, 25b and 26 are all 0V as shown in FIG.

In the period t2 shown in FIG. 18C, a current flows only through the first partial LED row 23a. If the potential difference generated in the current detection resistor 203 in the period t2 is V _{sen_t2} , the gate-source voltage Vgs of the _{FET 25a} is −g _b1 × V _{sen_t2} , and the gate-source voltage Vgs of the _{FET 25b} is −g _b2 × V _{sen_t2} . Further, the gate-source voltage Vgs of the _{FET 26} is −g _c × V _{sen — t 2} . −g _b1 × V _{sen — t2,} which is the gate-source voltage Vgs of the FET 25a, is equal to _Vgs1a in FIGS. 18 (a) and 18 (c).

In the period t3 shown in FIG. 18C, a current flows through the first partial LED row 23a and the second partial LED row 23b. When the potential difference generated in the current detection resistor 203 in the period t3 is V _{sen_t3} , the gate-source voltage Vgs of the _{FET 25a} is −g _b1 × V _{sen_t3} , and the gate-source voltage Vgs of the _{FET 25b} is −g _b2 × V _{sen_t3} . The gate-source voltage Vgs of the _{FET 26} is −g _c × V _{sen — t3} . -G _b2 × V _{sen — t2,} which is the gate-source voltage Vgs of the FET 25b, is equal to _Vgs1b in FIGS. 18 (a) and 18 (c).

In a period t4 shown in FIG. 18C, a current flows through all of the first partial LED row 23a, the second partial LED row 23b, and the third partial LED row 24. When the potential difference generated in the current detection resistor 203 in the period t4 is V _{sen_t4} , the gate-source voltage Vgs of the _{FET 25a} is −g _b1 × V _{sen_t4} , and the gate-source voltage Vgs of the _{FET 25b} is −g _b2 × V _{sen_t4} . Further, the gate-source voltage Vgs of the _{FET 26} is −g _c × V _{sen — t 4} . -G _c × V _{sen — t4,} which is the gate-source voltage Vgs of the _{FET 26,} is equal to Vgs2 in FIGS. 18 (a) and 18 (c).

  FIG. 19A is a diagram showing the relationship between the voltage-current characteristics of the FETs 25a, 25b, and 26 and the voltage-current characteristics of the current control units of the first bypass circuit 201a, the second bypass circuit 101b, and the current limiting circuit 202. It is. FIG. 19B is a partially enlarged view of the diagram shown in FIG. 19A and 19B, the horizontal axis indicates the gate-source voltage Vgs of the FETs 25a, 25b, and 26, and the vertical axis indicates the drain current of the FETs 25a, 25b, and 26. In each of FIGS. 19A and 19B, the solid lines indicate the voltage-current characteristics of the FETs 25a, 25b and 26, and the broken lines indicate the voltage-current characteristics of the first bypass circuit current control unit 270a. The alternate long and short dash line indicates the voltage-current characteristic of the second bypass circuit current control unit 270b, and the alternate long and two short dashes line indicates the voltage-current characteristic of the current limiting circuit current control unit 271.

The voltage-current characteristic of the first bypass circuit current control unit 270a is
Vgs = −g _b1 × R _s × Ids
The voltage-current characteristic of the second bypass circuit current control unit 270b is
Vgs = −g _b2 × R _s × Ids
The voltage-current characteristics of the current limiting circuit current control unit 271 are as follows:
Vgs = −g _c × R _s × Ids
It becomes the relationship. Here, R _s is the resistance value of the current detection resistor 203. The intersection of the voltage-current characteristic line of the first bypass circuit current control unit 270a, the second bypass circuit current control unit 270b and the current limiting circuit current control unit 280 and the voltage-current characteristic curve of the FET voltage-current characteristic is the operation of the FET. It becomes a point. By determining the gains g _b1 , g _b2, and g _c of the first bypass circuit variable power source 272a, the second bypass circuit variable power source 272b, and the current limiting circuit variable power source 282, the first partial LED row 23a, the second LED 23b, and the third The current flowing through the partial LED string 24 is determined.

  20 (a) to 20 (c) are circuit block diagrams of LED lighting devices in which semiconductor devices each having two bypass circuits and one current limiting circuit are connected in series.

  The LED lighting device 300 includes a bridge rectifier 11, a commercial AC power supply 12, a first partial LED row 13 a to a sixth partial LED row 13 f, a first semiconductor device 301, and a second semiconductor device 302. The bridge rectifier 11 and the commercial AC power supply 12 have the same functions and configurations as those of the LED lighting device 100. Further, each of the first partial LED row 13a to the sixth partial LED row 13f includes LEDs connected in series.

  Similar to the LED driving circuit 111, the first semiconductor device 301 includes a first bypass circuit 101 a and a second bypass circuit 101 b, a current limiting circuit 102, and a current detection resistor 103. The second semiconductor device 302 is different from the first semiconductor device 301 in that it does not have the current detection resistor 103. The drain of the FET of the first bypass circuit 101a of the first semiconductor device 301 is connected between the first partial LED row 13a and the second partial LED row 13b. The drain of the FET of the second bypass circuit 101b of the first semiconductor device 301 is connected between the second partial LED row 13b and the third partial LED row 13c. The drain of the FET of the current limiting circuit 102 of the first semiconductor device 301 is connected between the third partial LED string 13c and the fourth partial LED string 13d. The drain of the FET of the first bypass circuit 101a of the second semiconductor device 302 is connected between the fourth partial LED row 13d and the fifth partial LED row 13e. The drain of the FET of the second bypass circuit 101b of the second semiconductor device 302 is connected between the fifth partial LED row 13e and the sixth partial LED row 13f. The drain of the FET of the current limiting circuit 102 of the second semiconductor device 302 is connected to the cathode of the final stage LED of the sixth partial LED row 13f. The first semiconductor device 301 and the second semiconductor device 302 are connected in series by connecting the sources of the FETs of the first semiconductor device 301 and the second semiconductor device 302 to each other.

  The LED lighting device 310 is different from the LED lighting device 300 in that the first semiconductor device 301 and the second semiconductor device 302 are not connected in series, but the two first semiconductor devices 301 are connected in series. Different from the lighting device 300. In the LED lighting device 310, a circuit that controls the currents of the first partial LED row 13a to the sixth partial LED row 13f is formed by connecting two first semiconductor devices 301 having the same configuration in series.

  The LED lighting device 320 is not the first semiconductor device 301 and the second semiconductor device connected in series like the LED lighting device 300 but the third semiconductor device 303 and the fourth semiconductor device 304 are connected in series. This is different from the LED lighting device 300. The third semiconductor device 303 and the fourth semiconductor device 304 are different from the first semiconductor device 301 in that they have a current detection resistor 103a and a current detection resistor 103b instead of the current detection resistor 103, respectively. The current detection resistor 103a and the current detection resistor 103b have different resistance values. In the LED lighting device 320, the gains of the bypass circuit and the current limiting circuit of the third semiconductor device 303 and the fourth semiconductor device 304 can be matched by making the resistance values of the current detection resistor 103a and the current detection resistor 103b different. . That is, in the LED lighting device 320, the gains of the first bypass circuit 101a of the third semiconductor device 303 and the fourth semiconductor device 304 are equal to each other, and the gains of the second bypass circuit 101b of the third semiconductor device 303 and the fourth semiconductor device 304 are equal. Are equal to each other. Further, the gains of the current limiting circuits 102 of the third semiconductor device 303 and the fourth semiconductor device 304 are equal to each other.

  21A to 21C are diagrams showing examples of the drain current Id of the FETs of the LED lighting devices 300 to 320, respectively.

21A to 21C, the drain currents Id of the FETs of the LED lighting devices 300 to 320 have the same waveform. In an example, in the LED lighting apparatuses 300 to 320, an AC voltage having an amplitude of 120V is applied to the commercial AC power supply 12, the threshold voltage of the FET is 3.8V, and the voltage of the reference power supply is 4.1V. Set to In the first semiconductor device 301 of the LED lighting device 300 and the first semiconductor device 301 in the preceding stage of the LED lighting device 310, the gain g _b1 of the first bypass circuit variable power source 172a is set to 12, and the second bypass circuit variable power source 172b The gain g _b2 is set to 8. In the first semiconductor device 301 of the LED lighting device 300 and the first semiconductor device 301 in the previous stage of the LED lighting device 310, the gain g _c of the current limiting circuit variable power source 182 is set to 4. In the second semiconductor device 302 of the LED lighting device 300 and the first semiconductor device 301 subsequent to the LED lighting device 310, the gain g _b1 of the first bypass circuit variable power source 172a is set to 3, and the second bypass circuit variable power source 172b The gain g _b2 is set to 2. In the second semiconductor device 302 of the LED lighting device 300 and the first semiconductor device 301 subsequent to the LED lighting device 310, the gain g _c of the current limiting circuit variable power source 182 is set to 1. In the third semiconductor device 303 of the LED lighting device 320, the gain g _b1 of the first bypass circuit variable power source 172a is set to 3, the gain g _b2 of the second bypass circuit variable power source 172b is set to 2, and the current limiting circuit is variable. The gain g _{c of the} power source 182 is set to 1. In the fourth semiconductor device 304 of the LED lighting device 320, the gain g _b1 of the first bypass circuit variable power source 172a is set to 3, the gain g _b2 of the second bypass circuit variable power source 172b is set to 2, and the current limiting circuit is variable. The gain g _{c of the} power source 182 is set to 1. The first semiconductor device 301 and the second semiconductor device 302 of the LED lighting device 300, the current detection resistor 103 of the first semiconductor device 301 of the LED lighting device 310, and the current detection resistor 103b of the fourth semiconductor device 304 of the LED lighting device 320. The resistance value is 1Ω. The resistance value of the current detection resistor 103a of the third semiconductor device 303 of the LED lighting device 320 is 4Ω.

  22A and 22B are circuit block diagrams of LED lighting devices in which semiconductor devices each having two bypass circuits and one current limiting circuit are connected in parallel.

  The LED lighting device 330 includes a bridge rectifier 11, a commercial AC power supply 12, a first partial LED row 13 a to a third partial LED row 13 c, a first semiconductor device 301, and a second semiconductor device 302. The bridge rectifier 11 and the commercial AC power supply 12 have the same functions and configurations as those of the LED lighting device 100. Each of the first partial LED row 13a to the third partial LED row 13c includes LEDs connected in series.

  The FET drains of the first bypass circuit 101a and the second bypass circuit 101b of the first semiconductor device 301 are connected between the first partial LED row 13a and the second partial LED row 13b. The drains of the FETs of the current limiting circuit 102 of the first semiconductor device 301 and the first bypass circuit 101a of the second semiconductor device 302 are connected between the second partial LED row 13b and the third partial LED row 13c. The drains of the FETs of the second bypass circuit 101b of the second semiconductor device 302 and the current limiting circuit 102 of the second semiconductor device 302 are connected to the cathodes of the LEDs in the final stage of the third partial LED row 13c. The first semiconductor device 301 and the second semiconductor device 302 are connected in parallel by connecting the sources of the FETs of the first semiconductor device 301 and the second semiconductor device 302 to each other.

  The LED lighting device 340 includes a bridge rectifier 11, a commercial AC power supply 12, a first partial LED row 13a to a third partial LED row 13c, and two first semiconductor devices 301 connected in parallel. The bridge rectifier 11 and the commercial AC power supply 12 have the same functions and configurations as those of the LED lighting device 100. Each of the first partial LED row 13a to the third partial LED row 13c includes LEDs connected in series.

  The FET drains of the first bypass circuits 101a of the two first semiconductor devices 301 are connected between the first partial LED row 13a and the second partial LED row 13b. The FET drains of the second bypass circuits 101b of the two first semiconductor devices 301 are connected between the second partial LED row 13b and the third partial LED row 13c. The drains of the FETs of the current limiting circuits 102 of the two first semiconductor devices 301 are connected to the cathodes of the LEDs in the final stage of the third partial LED row 13c. The two first semiconductor devices 301 are connected in parallel by connecting the ground-side terminals of the current detection resistors 103 of the two first semiconductor devices 301 to each other.

  FIGS. 23A and 23B are diagrams showing examples of the drain current Id of the FETs of the LED lighting devices 330 and 340, respectively.

23A and 23B, the drain currents Id of the FETs of the LED lighting devices 330 and 340 have the same waveform. In one example, in the LED lighting devices 330 and 340, an AC voltage having an amplitude of 120V is applied to the commercial AC power supply 12, the threshold voltage of the FET is 3.8V, and the voltage of the reference power supply is 4.1V. The resistance value of the current detection resistor 103b is 1Ω. In the first semiconductor device 301 of the LED lighting device 330, the gains g _b1 and g _b2 of the first bypass circuit variable power source 172a and the second bypass circuit variable power source 172b are set to 8, and the gain g _{c of the} current limiting circuit variable power source 182 is set. Is set to 4. In the second semiconductor device 302 of the LED lighting device 330, the gain g _b1 of the first bypass circuit variable power source 172a is set to 4, and the gains g _b2 and g _{c of} the second bypass circuit variable power source 172b and the current limiting circuit variable power source 182 are set. Is set to 2. In the two first semiconductor devices 301 of the LED lighting device 340, the gain g _b1 of the first bypass circuit variable power source 172a is set to 16, and the gain g _b2 of the second bypass circuit variable power source 172b is set to 8. The gain g _c of the current limiting circuit variable power source 182 is set to 4.

  The LED drive circuits 10, 20, 111 and 211 can control the FET drain current based on the voltage detected by a single current detection resistor, thus minimizing the power consumed by the current detection resistor. can do.

  Further, in the LED drive circuits 10, 20, 111, and 211, the leakage current is eliminated by setting the bypass circuit gain and the current limiting circuit gain used when defining the gate-source voltage of the FET to appropriate values. Can do.

  Further, in the LED lighting devices 300, 310, 320, 330, and 330, a control unit that controls a current applied to the LED by a semiconductor device having a single current detection resistor is formed. For this reason, even when a plurality of semiconductor devices forming the control unit are connected in series or in parallel, the connection relation of wirings does not become complicated.

  The LED drive circuits 20 and 211 having depletion type FETs do not have a configuration corresponding to the bypass circuit reference power source and the current limit circuit reference power source, but have a configuration corresponding to the bypass circuit reference power source and the current limit circuit reference power source. A configuration may be adopted. By adopting a configuration corresponding to the bypass circuit reference power supply and the current limit circuit reference power supply, the adjustable range is widened by the voltage and gain detected by the current detection resistor, so that no leakage current flows. It becomes easier to set.

10, 20, 111, 211, 80, 90 LED drive circuit 11, 21, 81, 91 Bridge rectifier 12, 22, 82, 92 Commercial AC power supply 13, 13a, 13b, 14, 23, 23a, 23b, 24, 83 , 84, 93, 94 LED row (first partial LED row, second partial LED row, third partial LED row)
15, 15a, 15b, 16, 25, 25a, 25b, 26, 85, 86, 95, 96 FET (first current limiting element, second current limiting element)
100, 110, 200, 210, 300, 310, 320, 330, 340, 800, 900 LED lighting device 101, 101a, 101b, 201, 201a, 201b, 801, 901 Bypass circuit (bypass circuit, second bypass circuit)
102, 202, 802, 902 Current limiting circuit 103, 203 Current detection resistor (current information detection element)
170, 170a, 170b, 270, 270a, 270b, 970 Bypass circuit current control unit (second current control unit)
180, 280, 980 Current limiting circuit current control unit (first current control unit)

Claims (5)

A pulsating voltage in a first partial LED string including a plurality of LEDs connected in series and an LED string including a plurality of LEDs connected in series and including a second partial LED string connected in series with the first partial LED string A current control circuit for controlling a current flowing in the LED string when is applied,
LED current flowing between the current limit circuit input terminal and the current limit circuit output terminal, including a current limit circuit input terminal and a current limit circuit output terminal connected to the cathode of the last stage LED of the second partial LED row Current limiting circuit to limit,
A bypass circuit input terminal connected between the first partial LED string and the second partial LED string; and a bypass circuit output terminal connected to the current limiting circuit output terminal; the bypass circuit input terminal and the bypass A bypass circuit that limits a bypass current flowing between circuit output terminals;
A current detection element connected to the current limit circuit output terminal and the bypass circuit output terminal,
The current limiting circuit limits the LED current based on current information detected by the current detection element and a predetermined first coefficient,
The bypass circuit limits the bypass current based on the current information detected by the current detection element and a second coefficient different from the predetermined first coefficient according to the state of the pulsating voltage. The current flowing from the first partial LED array to the current detection element via the bypass circuit is controlled so as to flow toward the second partial LED array without passing through the bypass circuit.
An LED current control circuit characterized by the above. The current limiting circuit includes: a first current limiting element that limits the magnitude of the LED current; a first current control unit that controls the first current limiting element using the current information and the first coefficient; Have
The bypass circuit includes a second current limiting element that limits the bypass current, and a second current control unit that controls the second current limiting element using the current information and the second coefficient. Item 2. The LED current control circuit according to Item 1. Each of the first current limiting element and the second current limiting element is a FET,
The first current control unit includes a first reference power supply, a first variable power supply whose voltage is determined using the current information and the first coefficient,
The second current control unit includes a second reference power source, a second variable power source whose voltage is determined using the current information and the second coefficient,
The gate-source voltage of the first current limiting element is obtained by subtracting the voltage of the first variable power supply from the voltage of the first reference power supply, and the gate-source voltage of the second current limiting element is the second reference power supply. The LED current control circuit according to claim 2, wherein the voltage of the second variable power source is subtracted from the voltage.   The LED current control circuit according to claim 3, wherein the first coefficient and the second coefficient, and the voltages of the first reference power source and the second reference power source are variable. The LED string includes a plurality of LEDs connected in series, and further includes a third partial LED string connected in series between the first partial LED string and the second partial LED string, and the bypass circuit input terminal Is connected between the first partial LED string and the third partial LED string,
A second bypass circuit input terminal connected between the second partial LED string and the third partial LED string; and a second bypass circuit output terminal connected to the current limiting circuit output terminal; A second bypass circuit for limiting a second bypass current flowing between the second bypass circuit terminal input terminal and the second bypass circuit terminal output terminal;
The second bypass circuit includes a third coefficient different from the predetermined first coefficient and the second coefficient, and the current information detected by the current detection element according to the state of the pulsating voltage. The second bypass current is limited based on the current, and the current flowing from the third partial LED array to the current detection element via the second bypass circuit is passed through the second bypass circuit without passing through the second bypass circuit. The LED current control circuit according to any one of claims 1 to 4, wherein the LED current control circuit is controlled to flow toward a two-part LED array.

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