JP2006278526A - Light emitting diode drive device - Google Patents

Abstract

When the temperature of the light emitting diode rises, there is a problem that the allowable forward current value of the light emitting diode changes and the light emitting diode is damaged.
A switching drive circuit for supplying a current to a light emitting diode includes a switching element block including a switching element and a junction FET, and controls a current of the switching element with respect to a variation in an allowable forward current due to a temperature change of the light emitting diode. A control circuit block including a control circuit including a protection circuit. When the temperature of the light emitting diode rises, the control circuit block decreases the on-duty ratio of the switching element block and decreases the average current. Therefore, an excessive current is prevented from flowing through the light emitting diode, and the light emitting diode is prevented from being damaged.
[Selection] Figure 1

Description

  The present invention relates to a light emitting diode driving device, and more particularly to a lighting device using a light emitting diode.

Light emitting diodes (hereinafter referred to as LEDs) are widely used in various lighting devices because of their high luminous efficiency and long life. A conventional example of a light emitting diode driving device for lighting an LED will be described below. FIG. 11 is a circuit diagram of a light emitting diode driving apparatus of the first conventional example shown in Patent Document 1. In FIG. In the LED driving device of FIG. 11, full-wave rectification of alternating current is performed by a full-wave rectification circuit DB connected to an alternating-current power supply AC, and direct current is output between the switch contact S2 (+) and the circuit ground G (−). . A direct current obtained by half-wave rectification of the alternating current AC is output between the switch contact S1 (+) and the circuit ground G (−). Current limiting elements Z1 to Zm are connected to LED arrays 1 to m in which a plurality of LEDs are connected in series between each of the switch contacts A1, A2,. A series connection body connected in series is connected. That is, serially connected bodies having a length from 1 to m (m is an integer of 2 or more) are connected between the switch contacts A1 to Am and the circuit ground G.
In this conventional LED driving device, when m is 2, that is, when the two LED arrays 1 and 2 are connected to the switch contacts A1 and A2, respectively, the switch contacts A1 and A2 are connected to the switch contact S1, The light intensity can be adjusted (dimmed) in four steps by the combination of separating and contacting S2.

FIG. 12 is a circuit diagram of a light emitting diode driving device of a second conventional example shown in Patent Document 2. In FIG.
The LED driving device of FIG. 12 includes an LED 101 as a current driving element that emits light when supplied with direct current, and a coil 102 connected in series to the LED 101. A diode 103 is connected in antiparallel to the LED 101 and the coil 102. The diode 103 is provided to supply the back electromotive force generated in the coil 102 to the LED 101.
As a power supply unit for applying a pulse voltage to the LED 101, the coil 102, and the diode 103, a DC power supply 105 and a switching element 104 that functions as a switch for interrupting the output of the DC power supply 105 are provided. The switching element 104 includes, for example, a switching transistor and an oscillator (not shown). The cathode of the diode 103 is connected to the positive output terminal of the DC power source 105.

In the light emitting diode driving device of the second conventional example, when the switching element 104 is turned on / off according to a desired light emission timing for causing the LED 101 to emit light, the output voltage of the DC power source 105 is intermittently applied to the coil 102 and the LED 101. Is done. Figure 13 (a) shows a control pulse (switching pulse) SW applied to the switching element 104, the (b) and (c) current I _LED flowing through the current I _L and LED101 flowing through the coil 102, respectively Is shown. As shown in FIG. 13A, the switching element 104 is turned on at the falling edge of the switching pulse SW input to the switching element 104. When the switching element 104 is turned on, the DC voltage VDD from the DC power source 105 is applied to the coil 102 and the diode 103. Since the diode 103 is reverse-biased, no current flows. As shown in FIGS. 13B and 13C, when the switching pulse SW is in the “L” state, a current I _L flows through the coil 102, and the same amount of current I also flows through the LED 101 connected in series with the coil 102. _{The LED} flows and the _LED 101 emits light. The current values of the current I _L and the current I _LED change with time t. Current I _L of the coil 102 increases until 0～I0, increased to 0～I0 also current I _LED flowing through the LED 101.

Next, as shown in FIG. 13A, when the switching element 104 is turned off at the rising edge of the switching pulse SW, the application of the voltage from the DC power source 105 is cut off, and a back electromotive force is generated in the coil 102. . This back electromotive force causes a current I _L to flow through the coil 102. The current I _L varies with time t and decreases from i0 to 0. Counter electromotive voltage generated in the circuit, so is applied to the forward direction LED101 and diode 103, the current I _L of the coil 102 through the LED101 and the diode 103. Accordingly, as shown in FIG. 13C, the current I _LED flows to the _LED 101 while decreasing from i0 to 0, and the _LED 101 emits light by this current.

According to the light emitting diode driving apparatus of the second conventional example, when the switch by the switching element 104 is turned on, the LED 101 is caused to emit light by applying the output voltage from the DC power source 105, and the switch is turned off. Sometimes, the LED 101 is caused to emit light by utilizing the back electromotive force of the coil 102.
JP 2000-30877 A Japanese Patent Laid-Open No. 2001-8443

  The light emitting diode driving device of the first conventional example shown in Patent Document 1 has the following problems. The current value of each LED array 1 to m is determined by the value of current limiting elements Z1 to Zm such as resistors. Therefore, when the LED temperature rises and the forward resistance of the LED decreases, the current increases, and when a mismatch between the current limiting element and the temperature characteristics of the LED occurs, depending on changes in the current values of the LED arrays 1 to m, it is acceptable. Current exceeding the forward current may flow through the LED, causing the LED to break.

  The conventional light emitting diode driving device disclosed in Patent Document 2 has the same problem. Since the switching element 104 is simply a combination of a switching transistor and an oscillator, the forward current of the LED 101 increases when the temperature of the LED 101 and the temperature of the switching transistor rise. Therefore, the LED 101 may be damaged.

  An object of the present invention is to provide a light emitting diode driving device in which an LED is not easily damaged even when an energization current changes with temperature.

A light emitting diode driving device according to claim 1 is a light emitting diode block having at least one light emitting diode, a choke coil connected in series to the light emitting diode block, and the choke coil connected in series and the light emitting diode block in parallel. A diode that is connected and supplies back electromotive force generated in the choke coil to the light emitting diode block, a direct current power source that supplies direct current to the light emitting diode block and the choke coil, and a direct current that is supplied to the light emitting diode block is turned on / off Switching circuit
The switching circuit includes a switching element block having at least one switching element, an on-duty ratio changing circuit for changing an on-duty ratio of the switching element based on a temperature change of the light-emitting diode, and an output voltage of the DC power supply being a predetermined value At this time, the switching element is on / off controlled at a predetermined oscillation frequency, and when the output voltage is lower than the predetermined value, a start / stop circuit that stops the on / off control, and a current detection that detects a current flowing through the switching element And a control circuit block having a control circuit that receives a detection signal from the current detection circuit and performs on / off control so that an average current flowing through the switching element becomes constant at a predetermined on-duty ratio. Features.

  According to the present invention, when the switching element is in the ON state, a current flows in the direction of the choke coil → the light emitting diode → the switching element. When the switching element is in the OFF state, a current flows through the circuit loop including the choke coil, the light emitting diode, and the diode in the direction of the choke coil → the light emitting diode → the diode, and operates similar to the step-down chopper. Therefore, the power conversion efficiency is high, and the average current flowing through the light emitting diode block can be controlled to be constant even when the input voltage varies. Since the light emitting diode driving device of the present invention performs an on / off operation with a voltage having a predetermined on-duty ratio, the ratio of the period during which current flows and the period during which current does not flow can be adjusted in one cycle. That is, since the current flowing through the switching element can be controlled with respect to a change in the temperature of the light emitting diode, a light emitting diode driving device that prevents damage to the LED even when the temperature changes can be realized.

According to a second aspect of the present invention, the on-duty ratio changing circuit changes the on-duty ratio of the switching element based on a change in the forward voltage of the light-emitting diode due to temperature.
According to the present invention, the current of the light emitting diode when the temperature changes is controlled by changing the on-duty ratio based on the change of the forward voltage of the light emitting diode with the temperature.

According to a third aspect of the present invention, the on-duty ratio changing circuit includes temperature detecting means for detecting a temperature of the light-emitting diode block.
According to the present invention, the temperature change is detected by the temperature detection means, and the on-duty ratio is changed by the detection output to control the current of the light emitting diode. This prevents an excessive current from flowing through the light emitting diode when the temperature rises.

  According to a light emitting diode driving apparatus of a fourth aspect of the present invention, the switching element block has a control terminal, a high potential side terminal, and a low potential side terminal, and the control terminal controls the output terminal of the control circuit block and the switching element. A terminal is connected, one output terminal of the switching element and the ground terminal of the control circuit block are connected to the low potential side terminal, an input terminal of the junction FET is connected to the high potential side terminal, and the junction The other output terminal of the switching element and the input terminal of the control circuit block are connected to the output terminal of the type FET.

  In the light emitting diode driving device according to the fifth aspect of the present invention, the switching element block has a control terminal, a high potential side terminal, and a low potential side terminal, and the control terminal includes an output terminal of the control circuit block and the switching element. A control terminal is connected, one output terminal of the switching element and the ground terminal of the control circuit block are connected to the low potential terminal, and an input terminal of the junction FET and the other of the switching element are connected to the high potential side terminal. The output terminal of the control circuit block is connected to the output terminal of the junction FET.

  According to a sixth aspect of the present invention, the switching element block has a control terminal, a rectified voltage source terminal, a high potential side terminal, and a low potential side terminal, and the control terminal is an output terminal of the control circuit block. And the control terminal of the switching element is connected, one output terminal of the switching element and the ground terminal of the control circuit block are connected to the low potential terminal, and the other output terminal of the switching element is connected to the high potential side terminal Is connected to the output terminal of the rectifier circuit that rectifies an AC voltage and the input terminal of the junction FET, and the input terminal of the control circuit block is connected to the output terminal of the junction FET. It is characterized by that.

  According to the inventions of claims 3, 4, 5 and 6, in addition to the above effect, the high voltage applied to the high potential side of the junction FET is reduced by the pinch-off effect of the junction FET. Is pinched off at a low voltage. Therefore, power can be supplied from the switching element block to the control circuit, and power loss due to the starting resistance and the like is reduced. Further, the light emitting diode can be prevented from being destroyed by adjusting the current in accordance with the change in the allowable forward current of the light emitting diode due to the temperature rise.

  According to the present invention, when the temperature of the light emitting diode changes and the allowable forward current changes, the average current flowing through the light emitting diode is changed stepwise according to the temperature change. Accordingly, it is possible to prevent an excessive current due to a temperature change from flowing through the light emitting diode and prevent the light emitting diode from being damaged.

Hereinafter, preferred embodiments of the light emitting diode driving device of the present invention will be described with reference to FIGS.
Embodiment 1

A light emitting diode driving apparatus according to a first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a circuit diagram of a light-emitting diode driving apparatus according to Embodiment 1 of the present invention.
One end of the choke coil 3 and the cathode terminal of the diode 4 are connected to the high potential side (positive terminal 2a) of the full-wave rectifier circuit 2 connected to the AC power source 1. The other end of the choke coil 3 is connected to the anode terminal of the uppermost light emitting diode 5a in the figure of the light emitting diode array 5. The light emitting diode array 5 is a light emitting diode block in which one or a plurality of diodes are connected in series. The input terminal VD on the high potential side of the switching element block 7 in the control circuit 6 and the anode terminal of the diode 4 are connected to the cathode terminal of the lowermost light emitting diode 5b.

  The switching element block 7 is composed of a serial connection body of a switching element 9 of a junction FET (hereinafter referred to as a junction FET 9) and a switching element 10 of an FET, and the drain terminal of the junction FET 9 is connected to the input terminal VD on the high potential side. The source terminal of the junction FET 9 is connected to the connection point 7a of the low potential side terminal, and the control terminal is connected to the ground terminal G. An input terminal VJ of the control circuit block 8 is connected to a connection point 7 a between the junction FET 9 and the switching element 10. The output terminal 8 a of the control circuit block 8 is connected to the control terminal of the switching element 10.

  The control circuit block 8 has a rectified voltage terminal IN1, an input terminal VJ, an input terminal VD, an output terminal 8a, a ground terminal G, a reference voltage terminal 36, and a VF voltage terminal IN2. The rectified voltage terminal IN1 is connected to the input voltage detection circuit 21. A capacitor 24 is connected between the reference voltage terminal 36 and the ground terminal G. The input terminal VJ is connected to one end of the regulator 11 and a detection terminal of the drain current detection circuit 18 (current detection circuit) to which the detection reference voltage Vsn is input. The other end of the regulator 11 is connected to the reference voltage terminal 36. The first terminal 27a of the VF voltage detection circuit 27 is connected to the input terminal VD, and the second terminal 27b of the VF voltage detection circuit 27 is connected to the VF voltage terminal IN2. The first and second terminals 27a and 27b of the VF voltage detection circuit 27 are connected to both terminals of the light emitting diode 5b, respectively, and detect the forward voltage VF (acronym for Voltage Forward). The output of the VF voltage detection circuit 27 is input to an on-duty ratio changing circuit 35 having a detailed circuit configuration shown in FIG. The ON duty ratio changing circuit 35 receives the MAX DUTY signal 19a, the output signal 27c of the VF voltage detection circuit 27, the clock signal 19b, the input voltage VJ, and the output signal 14a of the on-time blanking pulse generator, and the output signal 35a. Is output to the AND circuit 13.

  The output terminal 8 a of the AND circuit 13 is connected to the control terminal of the switching element 10 of the switching element block 7 and the input terminal of the on-time blanking pulse generator 14. The four input terminals of the AND circuit 13 include an output terminal from which the output signal of the start / stop circuit 12 is output, a MAX DUTY signal output terminal of the oscillator 19, an output terminal Q of the RS flip-flop circuit 15, and an on-duty ratio change circuit 35. An output terminal 35a is connected. The input terminal of the AND circuit 17 is connected to the output terminal of the drain current detection circuit 18 and the output terminal of the on-time blanking pulse generator 14. The output signal of the AND circuit 17 and the inverted signal of the MAX DUTY signal of the oscillator 19 are input to the two input terminals of the OR circuit 16, respectively, and the output signal is input to the reset signal terminal R of the RS flip-flop circuit 15.

  The input voltage detection circuit 21 includes a comparator 20 to which the detection reference voltage Vst is input to the (−) terminal, and two resistors 22 and 23 connected in series. The high potential side of the resistors 22 and 23 connected in series is connected to the rectified voltage terminal IN 1 of the control circuit block 8, and the low potential side is connected to the ground terminal G of the control circuit block 8. The connection point of the resistors 22 and 23 is connected to the (+) terminal of the comparator 20. The output terminal of the comparator 20 is connected to the input terminal of the start / stop circuit 12.

2A shows a voltage waveform of the voltage Vin at the positive terminal 2a in the light emitting diode driving apparatus shown in FIG. 1, and FIG. 2B shows a current waveform (IL) flowing through the light emitting diode array 5. FIG. FIG. 2C shows a voltage waveform of the reference voltage Vcc.
FIG. 3 is a graph showing the relationship between the two input voltages with the input voltage VD on the horizontal axis and the input voltage VJ on the vertical axis. The operation of the light-emitting diode driving apparatus according to the first embodiment of the present invention will be described with reference to FIGS.

  The voltage Vin output from the full-wave rectifier circuit 2 has a waveform obtained by full-wave rectifying the AC voltage as shown in FIG. The full-wave rectified voltage Vin is applied from the input terminal VD to the high potential side of the junction FET 9 of the switching element block 7 through the choke coil 3 and the light emitting diode array 5. When the input voltage VD on the horizontal axis in FIG. 3 gradually increases, the input voltage VJ on the low potential side also increases as the input voltage VD increases (area A). When the input voltage VD further rises and becomes equal to or higher than the pinch-off voltage VDP, the FET 9 is pinched off and the input voltage VJ becomes equal to the voltage VJP (region B).

  Due to the current supplied from the regulator 11 connected to the low potential side of the junction FET 9, the voltage Vcc of the reference voltage terminal 36 of the control circuit block 8 also rises. When the high-potential side input voltage VD becomes the voltage VDSTART (FIG. 3) and the low-potential side input voltage VJ reaches the starting voltage Vcc0 ((c) in FIG. 2), the voltage Vcc is always kept constant by the regulator 11. Control is performed to Vcc0, and oscillation of the oscillator 19 of the control circuit block 8 is started. When the voltage at the reference voltage terminal 36 falls below the starting voltage Vcc0, the oscillation of the oscillator 19 is stopped.

  The voltage Vin is applied to the high potential side of the resistor 22 in the input voltage detection circuit 21 through the rectified power supply terminal IN1, and the voltage Vin ′ divided by the resistors 22 and 23 is applied to the (+) terminal of the comparator 20. The A predetermined reference voltage Vst is applied to the (−) terminal of the comparator 20. When the voltage Vin ′ divided by the resistors 22 and 23 reaches the reference voltage Vst, the comparator 20 is activated by the start / stop circuit 12. Send a signal. The activation signal is applied to the gate of the switching element 10 via the AND circuit 13 and controls the activation of the switching element 10.

  At this time, as shown in FIG. 2A, the voltage Vin1 when the voltage Vin ′ reaches the reference voltage Vst is set higher than the voltage Vin2 when the input voltage VJ reaches the starting voltage Vcc0. Therefore, intermittent ON / OFF control of the switching element 10 by the control circuit block 8 is started. When the voltage Vin 'divided by the resistors 22 and 23 falls below the reference voltage Vst, the comparator 20 sends a stop signal to the start / stop circuit 12, and the control circuit block 8 keeps the switching element 10 in the OFF state.

  That is, as shown in FIG. 2B, on / off control of the switching element 10 is performed during a period T <b> 1 where the voltage Vin ′ is equal to or higher than the reference voltage Vst, and a constant current IL flows through the light emitting diode array 5. During the period T <b> 2 where the voltage Vin ′ is smaller than the reference voltage Vst, the switching element 10 remains off, and no current flows through the light emitting diode array 5.

A constant current output operation in the case where the temperature of the diode array 5 of the light emitting diode driving apparatus according to the first embodiment is constant will be described with reference to FIG.
In response to the start signal from the start / stop circuit 12, the output of the oscillator 19 is output from the AND circuit 13, and the on / off control of the switching element 10 by the control circuit block 8 is started. The switching frequency and on-duty ratio of the switching element 10 (duty ratio when the switching element 10 is turned on) are determined by the CLOCK signal and the MAX DUTY signal of the oscillator 19, respectively. The current flowing through the switching element 10 is detected by comparing the ON voltage (input voltage VJ) of the switching element 10 with the detection reference voltage Vsn of the drain current detection circuit 18. When the ON voltage of the switching element 10 reaches the detection reference voltage Vsn, the switching element 10 is turned off until the next CLOCK signal of the oscillator 19 enters the input S of the RS flip-flop 15. That is, the on-duty ratio of the switching element 10 is determined by the inverted signal of the MAX DUTY signal output from the oscillator 19 and the output signal of the OR circuit 16 to which the output signal of the drain current detection circuit 18 is input.

An ON-time blanking pulse generator 14 is connected to the control terminal of the switching element 10, and an output signal of the ON-time blanking pulse generator 14 and an output signal of the drain current detection circuit 18 are input to the AND circuit 17. The Occurs when the switching element 10 changes from the off state to the on state by inputting the output of the AND circuit 17 and the MAX DUTY signal to the OR circuit 16 and applying the output of the OR circuit to the input R of the RS flip-flop 15. A malfunction of on / off control of the switching element 10 due to ringing is prevented. The VF voltage detection circuit 27 detects the voltage VF of one (or a plurality of) light-emitting diodes 5b connected between the VF voltage input terminal IN2 and the input terminal VD and inputs it to the on-duty ratio changing circuit 35. . The on-duty ratio changing circuit 35 outputs a signal for changing the on-duty ratio according to the VF voltage to the AND circuit 13. As a result, the on-duty ratio of the output of the AND circuit 13 changes, so that the on-duty ratio of the switching element 10 also changes and the current flowing through the switching element 10 is controlled.
The above operation will be described in detail with reference to FIG. 4A shows the waveform of the input voltage VD, and FIG. 4B shows the reference voltage Vcc at a constant level.

  The switching element 10 is on / off controlled by the control circuit block 8, and the current ID flowing through the switching element 10 is as shown in FIG. That is, when the switching element 10 is in the ON state, a current ID having a peak peak current IDP flows through the choke coil 3 → the light emitting diode array 5 → the junction FET 9 → the switching element 10 in the direction of the arrow. When the switching element 10 is in the OFF state, the current flows in the direction of the arrow through the closed loop of the choke coil 3 → the light emitting diode array 5 → the diode 4. As a result, the current IL flowing through the choke coil 3 (that is, the current flowing through the light emitting diode array 5) has a sawtooth waveform having a peak value IDP as shown in FIG. 4D and flows through the light emitting diode array 5. The average current is the current IL0 shown in FIG. As a result, the diode array 5 is lit at a substantially constant luminous intensity. FIG. 4E shows the levels of the voltage VJ and the voltage Vsn. FIG. 4F shows the temperature T of the diode array 5.

  Next, the operation when the temperature of the light-emitting diode array 5 rises in the light-emitting diode driving device of the first embodiment will be described with reference to FIG. As shown in FIG. 5F, when the temperature T of the light emitting diode array 5 rises with the passage of time t, the forward resistance of the light emitting diode 5b falls, so the voltage VF also falls with the passage of time t. The voltage VF is detected by the VF voltage detection circuit 27, and the detection output is applied to the on-duty ratio changing circuit 35. The on-duty ratio changing circuit 35 applies a pulse output that changes the on-duty ratio in, for example, three stages according to the level of the detection output to the AND circuit 13 through the connection line 35a. As a result, the current ID flowing through the switching element 10 that is ON / OFF controlled by the output of the AND circuit 13 is as shown in FIG. 5C, and the voltage VD is as shown in FIG.

  In FIG. 5, the on-duty ratio is “high” from time t0 to t1 when the temperature T is equal to or lower than the temperature T1. When the temperature T rises above T1, the on-duty ratio changes to “medium” at time t2, and this on-duty ratio is maintained until time t3 when the temperature T is equal to or lower than the temperature T2. When the temperature T further rises and exceeds T2, the on-duty ratio changes to “small” at time t4. In the above example, when the temperature T rises, the on-duty ratio is changed in three stages. However, this change is not limited to three stages, and may be changed in more stages. Further, the PWM control may be performed by changing continuously instead of changing stepwise.

As the on-duty ratio decreases, the peak value IDP of the current ID also decreases in three stages, as shown in FIG. This is because the electromagnetic energy stored in the coil 3 also decreases due to the decrease in the on-duty ratio. The current IL flowing through the light emitting diode array 5 becomes an average current ILO having a waveform shown in FIG.
According to the present embodiment, when the temperature of the light-emitting diode array 5 rises and the forward resistance decreases, the average current ILO flowing through the light-emitting diode array 5 is reduced, and an excessive current flows in the light-emitting diode array 5. Do not flow. Therefore, the light emitting diode driving device of the present embodiment is used for applications having a large temperature change, for example, when it is exposed to sunlight during the daytime and becomes a considerably high temperature (for example, 80 ° C.), and at night the temperature is greatly reduced (for example, 10 ° C.). The light emitting diode can be prevented from being destroyed even when used outdoors.

  In the above description, it has been described that the average current of the light emitting diode array 5 becomes smaller with respect to the change of the voltage VF of the light emitting diode 5b detected by the VF voltage detection circuit 27 due to the temperature. The light emitting diode array 5 may be operated so that the average current of the light emitting diode array 5 increases with respect to the fluctuation of the voltage VF. Further, the average current of the light-emitting diode array 5 may be linearly changed with respect to the change in the voltage VF of the light-emitting diode 5b, and these are the same in the following embodiments.

The effect of the light emitting diode driving apparatus of the first embodiment will be described in detail below.
In a normal light emitting diode, when the temperature rises, the forward resistance decreases and the allowable forward current decreases. In the conventional LED driving device, when the LED temperature rises, the forward resistance decreases and the LED current increases, the current value exceeds the LED's allowable forward current value and the LED is destroyed. May be.
In the light emitting diode driving apparatus according to the first embodiment, the change in the voltage VF of the light emitting diode that changes with a temperature rise is detected, the on-duty ratio of the current flowing through the switching element 10 is reduced according to the voltage VF, and the average current is increased. By reducing the ILO, the light emitting diode can be prevented from being damaged.

  Further, when the allowable forward current of the light emitting diode increases due to the temperature rise depending on the type of the light emitting diode, the luminous intensity of the light emitting diode can be adjusted by increasing the value of the current flowing through the switching element 10.

In the light emitting diode driving device according to the first embodiment, the switching element block 7 and the control circuit block 8 shown in FIG. 1 are formed on the same substrate to constitute the control device 6, so that the light emitting diode driving device is downsized. Is done. This configuration is the same in the following embodiments.
In the circuit of FIG. 1, the full-wave rectifier circuit 2 is used to rectify the alternating current of the AC power supply 1, but the same effect can be obtained even if a half-wave rectifier circuit is used. This also applies to each of the following embodiments.

  In the on / off operation of the switching element 10 by the control circuit block 8, when the switching element 10 shifts from the on state to the off state, the input voltage VD at the high voltage side terminal of the switching element block 7 causes the capacitance or inductance of the wiring. In some cases, the withstand voltage of the switching element 10 may be exceeded due to ringing caused by. In such a case, the switching element 10 may be destroyed.

In the present embodiment, in order to prevent destruction of the switching element 10, as shown in FIG. 1, a Zener diode 40 or the like is connected in parallel between the input terminal VD on the high potential side of the switching element block 7 and the circuit ground G on the low potential side. It is desirable to connect a clamp circuit. If the clamp voltage of the clamp circuit is set lower than the withstand voltage of the switching element 10, the input voltage VD of the switching element block 7 is clamped by this clamp voltage. Therefore, destruction of the switching element 10 can be prevented, and a light-emitting diode driving device with high safety can be realized.
In each of the following embodiments, the same effect can be obtained by adding a clamp circuit in the same manner.
<< Embodiment 2 >>

A light-emitting diode driving apparatus according to Embodiment 2 of the present invention will be described with reference to the circuit diagram of FIG.
In the light emitting diode driving apparatus according to the second embodiment shown in FIG. 6, a temperature detection circuit 28 is provided instead of the VF voltage detection circuit 27 shown in FIG. Other configurations are the same as the circuit configuration of the first embodiment shown in FIG.

  The temperature detection circuit 28 includes a temperature sensor 28a and detects the ambient temperature of the light emitting diode array 5 or the light emitting diode driving device. The output of the temperature detection circuit 28 is applied to the on-duty ratio changing circuit 35. The operation of the on-duty ratio changing circuit 35 is the same as that described in the first embodiment, and the on-duty ratio is changed by the detection output of the temperature detection circuit 28. The output of the on-duty ratio changing circuit 35 is applied to the AND circuit 13. The on-duty ratio of the gate voltage of the switching element 10 that is the output of the AND circuit 13 is changed by the output of the temperature detection circuit 28, and the current flowing through the switching element 10 is changed.

  With reference to FIG. 7, which is substantially the same as FIG. 5, the operation of the light emitting diode driving apparatus according to the second embodiment will be described. When the temperature changes as shown in FIG. 7 (f), the on-duty ratio is changed in three stages, for example, as shown in FIG. 7 (a) according to the change in temperature. As a result, as shown in FIG. 7C, the current ID flowing through the switching element 10 also changes in three stages. Since the PWM-controlled current ID shown in FIG. 7C flows through the switching element 10, the current flowing through the choke coil 3 becomes the current IL shown in FIG. 7D. The average current ILO of the light emitting diode array 5 is as shown in FIG.

  In the present embodiment, it has been described that the average current of the light emitting diode array 5 decreases with respect to the temperature change of the light emitting diode driving device or the light emitting diode array 5, but the average current of the light emitting diode array 5 increases. It may be operated. Further, the average current of the light emitting diode array 5 may be linearly changed with respect to the change in temperature.

The effect of the light emitting diode driving apparatus of the second embodiment will be described below. In the second embodiment, the current flowing through the light emitting diode array 5 is controlled according to the temperature of the light emitting diode array 5 or the ambient temperature of the light emitting diode driving device. Therefore, even if there is a variation in the voltage VF of each light emitting diode in the light emitting diode array 5, there is no risk of being affected by it. Therefore, even when the allowable forward current of the light emitting diode is reduced due to a change in ambient temperature, the light emitting diode can be prevented from being broken.
<< Embodiment 3 >>

A description will be given with reference to the light-emitting diode driving apparatus according to Embodiment 3 of the present invention and the circuit diagram of FIG.
In the light emitting diode driving apparatus according to the third embodiment of the present invention shown in FIG. 8, the connection method of the junction type FET 9 of the switching element block 7a is different from the circuit shown in FIG. In FIG. 8, the junction FET 9 has a gate connected to the ground G, and a source and a drain connected to the input terminal VD and the regulator 11, respectively. Furthermore, another switching element 25 is connected to the switching element 10 in parallel. The drain of the switching element 25 is connected to the ground G through the resistor 26 and to the drain current detection circuit 18. As a result, the detection method of the drain current detection circuit 18 is different from that of the first embodiment shown in FIG. 1, but the operation of the light emitting diode driving device of the third embodiment is substantially the same as that of the first embodiment. is there.
The input of the drain current detection circuit 18 in the third embodiment is a voltage at the connection point 26a of the series connection body of the switching element 25 and the resistor 26 in which a current having a constant current ratio is smaller than the current flowing in the switching element 10. is there. That is, the voltage generated across the resistor 26 by the current flowing through the switching element 25. With such a configuration, since a large current does not flow directly through the resistor 26, power loss is reduced.
<< Embodiment 4 >>

A light-emitting diode driving apparatus according to Embodiment 4 of the present invention will be described with reference to the circuit diagram of FIG.
The light emitting diode driving apparatus according to the fourth embodiment shown in FIG. 9 has the same circuit configuration as that of the third embodiment shown in FIG. 8 except that the connection of the junction FET 9 of the switching element block 7 is different.

The input of the drain current detection circuit 18 in the fourth embodiment is a voltage at a connection point 26a of a series connection body of the switching element 25 and the resistor 26 in which a current having a constant current ratio is smaller than the current flowing in the switching element 10. is there. That is, the voltage generated across the resistor 26 by the current flowing through the switching element 25. With such a configuration, since a large current does not flow directly through the resistor 26, power loss is reduced.
In the third and fourth embodiments, the configuration including the VF voltage detection circuit 27 is illustrated, but the same effect can be obtained even if the VF voltage detection circuit 27 is replaced with the temperature detection circuit 28 as in the second embodiment. It is done.

  It can be used for devices and devices using light emitting diodes such as LED lighting devices.

1 is a circuit diagram of a light-emitting diode driving apparatus according to Embodiment 1 of the present invention. Waveform diagram showing the operation of the LED driving device of FIG. Graph explaining the operation of junction FET Waveform diagram showing the operation of the LED driving device of FIG. 1 when the temperature is constant Waveform diagram showing the operation when the temperature of the LED driving device of FIG. Circuit diagram of light-emitting diode driving apparatus according to Embodiment 2 of the present invention FIG. 6 is a waveform diagram showing the operation when the temperature of the LED driving device of FIG. 6 rises. Circuit diagram of light-emitting diode driving apparatus according to Embodiment 3 of the present invention Circuit diagram of light-emitting diode driving apparatus according to Embodiment 4 of the present invention Circuit diagram showing the internal configuration of the on-duty ratio changing circuit 35 Circuit diagram showing the configuration of a conventional LED driving device Circuit diagram showing the configuration of another conventional LED driving device In the LED driving apparatus of FIG. 12, a waveform diagram of the switching pulse SW applied to the switching element 104 and the current flowing through the coil 102 and the LED 101.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 AC power supply 2 Rectifier circuit 3 Choke coil 4 Diode 5 Light emitting diode array 7 Switching element block 8 Control circuit block 9 Junction type FET
DESCRIPTION OF SYMBOLS 10 Switching element 11 Regulator 12 Start / stop circuit 13 AND circuit 14 ON time blanking pulse generator 15 RS flip-flop circuit 16 OR circuit 17 AND circuit 18 Drain current detection circuit 19 Oscillator 20 Comparator 21 Input voltage detection circuit 22, 23, 26 Resistance 24 Capacitor 25 N-type MOSFET
27 VF voltage detection circuit 28 Temperature detection circuit 35 On-duty ratio change circuit 101 Light emitting diode (LED)
102 Coil 103 Diode 104 Switching element 105 DC power supply

Claims (6)

A light emitting diode block having at least one light emitting diode;
A choke coil connected in series to the light emitting diode block;
A diode connected in parallel to the choke coil and the light emitting diode block connected in series, and supplying back electromotive force generated in the choke coil to the light emitting diode block;
A DC power supply for supplying a direct current to the light emitting diode block and the choke coil, and a switching circuit for turning on and off the direct current supplied to the light emitting diode block,
The switching circuit is
A switching element block having at least one switching element;
An on-duty ratio changing circuit for changing an on-duty ratio of the switching element based on a temperature change of the light-emitting diode;
A start / stop circuit for controlling on / off of the switching element at a predetermined oscillation frequency when the output voltage of the DC power supply is equal to or higher than a predetermined value, and stopping the on / off control when the output voltage is lower than the predetermined value;
A current detection circuit that detects a current flowing through the switching element; and a control circuit that receives a detection signal from the current detection circuit and performs on / off control so that an average current flowing through the switching element is constant at a predetermined on-duty ratio. A control circuit block having
A light-emitting diode driving device comprising:   2. The light emitting diode driving device according to claim 1, wherein the on duty ratio changing circuit changes an on duty ratio of the switching element based on a change in a forward voltage of the light emitting diode with temperature.   2. The light emitting diode driving device according to claim 1, wherein the on duty ratio changing circuit changes the on duty ratio based on an output of a temperature detecting means for detecting a temperature of the light emitting diode block. The switching element block has a control terminal, a low potential side terminal, and a high potential side terminal,
An output terminal of the control circuit block and a control terminal of the switching element are connected to the control terminal,
The output terminal of the switching element and the ground terminal of the control circuit block are connected to the low potential side terminal,
An input terminal of a junction FET is connected to the high potential side terminal,
4. The light emitting diode driving device according to claim 1, wherein the output terminal of the junction FET is connected to the other output terminal of the switching element and the input terminal of the control circuit block. The switching element block has a control terminal, a low potential side terminal, and a high potential side terminal,
An output terminal of the control circuit block and a control terminal of the switching element are connected to the control terminal,
The output terminal of the switching element and the ground terminal of the control circuit block are connected to the low potential side terminal,
The input terminal of the junction FET and the other output terminal of the switching element are connected to the high potential side terminal,
4. The light emitting diode driving device according to claim 1, wherein an input terminal of the control circuit block is connected to an output terminal of the junction FET. The switching element block has a control terminal, a low potential side terminal, a high potential side terminal, and a rectified voltage source terminal,
An output terminal of the control circuit block and a control terminal of the switching element are connected to the control terminal,
The output terminal of the switching element and the ground terminal of the control circuit block are connected to the low potential side terminal,
The other output terminal of the switching element is connected to the high potential side terminal,
An output terminal of the rectifier circuit that rectifies an AC voltage and an input terminal of a junction FET are connected to the rectified voltage source terminal,
4. The light emitting diode driving device according to claim 1, wherein an input terminal of the control circuit block is connected to an output terminal of the junction FET.

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