CN102271442B - LED drive circuit and control circuit - Google Patents

Abstract

The present invention provides a light emitting diode driving circuit and a control circuit for controlling a power conversion circuit to stabilize the output of the power conversion circuit. The control circuit comprises a capacitor, a charging unit, a discharging unit, a feedback control unit and a duty cycle adjustment unit. The charging unit has a current source connected to the capacitor for charging the capacitor. The discharging unit is connected to the capacitor for discharging the capacitor. The feedback control unit controls the charging unit to charge the capacitor according to a feedback signal representing the output state. The duty cycle adjustment unit generates a control signal and adjusts the duty cycle of the control signal according to the voltage of the capacitor.

Description

LED drive circuit and control circuit

technical field

The invention relates to a light emitting diode drive circuit and a control circuit.

Background technique

At present, electricity accounts for 14% of the world's annual energy, while lighting accounts for as much as 22% of the electricity usage. Therefore, under the current trend of global energy saving and carbon reduction, the impact of lighting plays a decisive role.

Today's common lighting sources are mainly incandescent lamps and fluorescent lamps. Although incandescent lamps are low in cost, they do not conform to the current trend of global low-carbon life due to the disadvantages of high energy consumption, low luminous efficiency, and high heat generation. Fluorescent tubes are made of glass and have sockets at both ends to connect to the power supply and fix the position of the fluorescent tubes. Unlike incandescent lamps, fluorescent tubes must be equipped with ballasts (also known as "ballasts"), which cooperate with starters to generate instantaneous high voltages that ionize gas to light fluorescent lamps. The advantages of fluorescent lamps are that the cost is low enough and the luminous efficiency is good enough. But this product is also accompanied by some usage problems, such as: flickering, warming up, etc. The flickering frequency of fluorescent lamps is related to the frequency of the driving voltage. Although it is not easy for the human eye to perceive the flicker of fluorescent lamps directly, these flickers will produce a fan effect in some environments, which will cause restrictions and impacts on some application environments. The preheating of fluorescent lamps will cause changes in brightness at the beginning of lighting and after a period of use. Therefore, the characteristics of light-emitting diodes such as long service life, high luminous efficiency, and stable and fast brightness are regarded as the main source of luminescence and lighting in the next era.

Light-emitting diodes can be used in a wide range of lighting fields, including indoor lighting, outdoor lighting, advertising signs, and backlight modules for electronic products. In the above application fields, the high cost and heat dissipation problems of LED backlights, which were criticized in the past, are being rapidly improved, and the overall penetration rate will continue to increase rapidly in the future. As light-emitting diodes replace today's lighting sources one by one, how to properly drive the light-emitting diodes as light sources and provide proper protection so that the light-emitting diodes can take advantage of their characteristics and improve the safety of use has become an important issue today.

Contents of the invention

In order to provide stable light emission for the light emitting diode, corresponding to different driving modes, the present invention enables the light emitting diode to provide stable light emission by way of current feedback and voltage feedback. And in order to avoid any circuit problems that may be encountered in the use of the LED driving circuit, the present invention additionally provides a protection function. When a problem that is sufficient to affect the normal operation of the circuit occurs, protection is provided to avoid further damage to the circuit.

To achieve the above purpose, the present invention provides a control circuit for controlling a power conversion circuit to stabilize the output of the power conversion circuit. The control circuit includes a capacitor, a charging unit, a discharging unit, a feedback control unit and a duty cycle adjustment unit. The charging unit has a current source connected to the capacitor for charging the capacitor. The discharge unit is connected to the capacitor for discharging the capacitor. The feedback control unit controls the charging unit to charge the capacitor according to a feedback signal representing the output state. The duty cycle adjustment unit generates a control signal and adjusts the duty cycle of the control signal according to the voltage of the capacitor.

The present invention also provides a light emitting diode driving circuit for driving a light emitting diode module, the light emitting diode module has a plurality of light emitting diode strings and the light emitting diode strings are connected in parallel. The LED drive circuit includes a current balance module, a first extreme voltage detection circuit, a power conversion circuit and a control circuit. The control circuit generates a control signal according to the feedback signal, which includes a capacitor, a charging unit, a discharging unit, a feedback control unit and a duty cycle adjustment unit. The current balancing module has a plurality of current balancing terminals correspondingly connected to a plurality of LED strings for balancing the current of the LED strings. The first terminal voltage detection circuit is connected to multiple current balance terminals, and generates a first feedback signal according to the highest potential or the lowest potential among the multiple current balance terminals. The power conversion circuit is connected with an input power, and converts the power of the input power according to a control signal to drive the LED module to emit light. The charging unit has a first current source connected to the capacitor for charging the capacitor. The discharge unit is connected to the capacitor for discharging the capacitor. The feedback control unit controls the charging unit to charge the capacitor according to the first feedback signal. The duty cycle adjustment unit generates a control signal and adjusts the duty cycle of the control signal according to the voltage of the capacitor.

The foregoing overview and the following detailed description are exemplary in nature. Other purposes and advantages of the present invention will be described in the subsequent description and accompanying drawings.

Description of drawings

FIG. 1 is a schematic circuit diagram of a LED driving circuit according to a first preferred embodiment of the present invention.

FIG. 2 is a schematic circuit diagram of a LED driving circuit according to a second preferred embodiment of the present invention.

FIG. 3 is a schematic circuit diagram of a LED driving circuit according to a third preferred embodiment of the present invention.

FIG. 4 is a schematic circuit diagram of a LED driving circuit according to a fourth preferred embodiment of the present invention.

Explanation of main reference signs:

100, 200: control circuit; 106: first comparator;

108: second comparator; 110, 210: duty cycle adjustment unit;

112, 212: feedback control unit; 114, 214: first switch;

115, 215: second switch; 116, 216: capacitance;

120, 220: pulse width modulator; 130, 230: drive circuit;

150, 250: light emitting diode module; 160, 260: power conversion circuit;

204: transient boost circuit; 206: timing circuit;

208: overvoltage comparator; 217: third switch;

222: Comparator; 224: RS flip-flop;

235: protection unit; 240: first extreme voltage detection circuit;

245: second extreme voltage detection circuit; 270: current balance module;

Vin: input power; Sc: control signal;

Vout: output voltage; L: inductance;

SW: Transistor switch; D: Rectifier diode;

C: output capacitor; Ri: feedback resistor;

FB: feedback signal; I1: first current source;

I2: second current source; I3: third current source;

Vr: reference voltage signal; S2: pulse width modulation signal;

Vr-, Vr1: the first reference voltage signal; Vr+, Vr2: the second reference voltage signal;

BD: bridge rectifier; VAC: AC input power supply;

T: transformer; D1～Dn: current balance terminal;

FB1: the first feedback signal; FB2: the second feedback signal;

FB3: The third feedback signal; OVP: Overvoltage protection signal;

S1: low protection signal; Ise: current detection signal;

S: Set terminal; R: Reset terminal;

Q: output terminal; DIM: dimming signal;

EN: start signal; VCC: drive power;

275: voltage detection circuit; Fault: error signal.

Detailed ways

Please refer to FIG. 1 . FIG. 1 is a schematic circuit diagram of a LED driving circuit according to a first preferred embodiment of the present invention. The LED driving circuit includes a control circuit 100 and a power conversion circuit 160 for driving an LED module 150 . The LED module 150 has a plurality of LEDs connected in series. The power conversion circuit 160 is connected to an input power Vin to convert (for example: step up or step down) the power of the input power Vin according to a control signal Sc to output an output voltage Vout to drive the LED module 150 to emit light. In this implementation, the power conversion circuit 160 is a DC-to-DC boost conversion circuit, including an inductor L, a transistor switch SW, a rectifier diode D and an output capacitor C. One end of the inductor L is connected to the input power Vin, the other end is connected to one end of the transistor switch SW, and the other end of the transistor switch SW is grounded. One end of the output capacitor C is connected to the connection point of the inductor L and the transistor switch SW through the rectifier diode D, and the other end is grounded. A feedback resistor Ri is connected to the LED module 150 to generate a feedback signal FB. The control circuit 100 receives the feedback signal FB to understand the power consumption of the LED module 150 according to the feedback signal FB, that is, the output state (ie, the magnitude of the current) of the power conversion circuit 160, so as to generate the control signal Sc accordingly, so that the LED Module 150 emits light steadily. The control circuit 100 includes a duty cycle adjustment unit 110 , a feedback control unit 112 , a charging unit, a discharging unit and a capacitor 116 . The charging unit has a first current source I1 and a first switch 114 , the first current source I1 is connected to the capacitor 116 through the first switch 114 to provide a charging current to charge the capacitor 116 . The discharge unit has a second current source I2 connected to the capacitor 116 to provide a discharge current to discharge the capacitor 116 . In this embodiment, the feedback control unit 112 is a comparator, the non-inverting terminal receives a reference voltage signal Vr, and the inverting terminal receives the feedback signal FB to control the first switch 114 to be turned on and off accordingly. The duty cycle adjustment unit 110 includes a pulse width modulator 120 and a driving circuit 130 . The pulse width modulator 120 can be a comparator, its non-inverting terminal receives a ramp signal, and its inverting terminal is connected to the capacitor 116 to generate a pulse width modulation signal S2 to the driving circuit 130 accordingly. The driving circuit 130 generates a control signal Sc according to the PWM signal S2 to control the transistor switch SW in the power conversion circuit 160 to be turned on and off, so as to adjust the output current of the power conversion circuit 160 .

When the current flowing through the LED module 150 is insufficient, the level of the feedback signal FB generated by flowing through the feedback resistor Ri is lower than the level of the reference voltage signal Vr, and the feedback control unit 112 generates a high level signal to make the first switch 114 conduction. At this time, the first current source I1 charges the capacitor 116 through the first switch 114 and the second current source I2 discharges the capacitor 116 at the same time. In this embodiment, the magnitude of the charging current provided by the first current source I1 is greater than the magnitude of the discharge current provided by the second current source I2. Therefore, when the first switch 114 is turned on, the voltage of the capacitor 116 will increase upwards. As the voltage of the capacitor 116 rises, the duty cycle of the pulse width modulation signal S2 output by the pulse width modulator 120 increases accordingly, so that the output current of the power conversion circuit 160 increases, thereby increasing the current flowing through the LED module 150 . When the current flowing through the LED module 150 is high enough to make the level of the feedback signal FB generated by flowing through the feedback resistor Ri higher than the level of the reference voltage signal Vr, the feedback control unit 112 generates a low level signal to make the first switch 114 is disconnected. At this time, the first current source I1 stops charging the capacitor 116 , while the second current source I2 continues to discharge the capacitor 116 , so that the voltage of the capacitor 116 gradually decreases. As the voltage of the capacitor 116 gradually decreases, the duty cycle of the pulse width modulation signal S2 output by the pulse width modulator 120 gradually decreases, so that the output current of the power conversion circuit 160 gradually decreases, and then gradually reduces the current flowing through the LED module. 150 current. When the current flowing through the LED module 150 is insufficient again, the control circuit 100 repeats the above steps. In this way, the current of the LED module 150 can be stabilized around a predetermined current value, so that the LED module 150 can stably emit light.

Please refer to FIG. 2 . FIG. 2 is a schematic circuit diagram of a LED driving circuit according to a second preferred embodiment of the present invention. Comparing this embodiment with the embodiment shown in FIG. 1 , the main difference lies in the way the control circuit 100 controls the charging and discharging of the capacitor 116 , which will be described as follows. The control circuit 100 includes a duty cycle adjustment unit 110 , a feedback control unit 112 , a charging unit, a discharging unit and a capacitor 116 . The charging unit has a first current source I1 and a first switch 114 , the first current source I1 is connected to the capacitor 116 through the first switch 114 to provide a charging current to charge the capacitor 116 . The discharge unit has a second current source I2 and a second switch 115 . The second current source I2 is connected to the capacitor 116 through the second switch 115 to provide a discharge current to discharge the capacitor 116 . The feedback control unit 112 includes a first comparator 106 and a second comparator 108 . The inverting terminal of the first comparator 106 receives the feedback signal FB generated by the feedback resistor Ri, and the non-inverting terminal receives a first reference voltage signal Vr−. The non-inverting terminal of the second comparator 108 receives the feedback signal FB generated by the feedback resistor Ri, and the inverting terminal receives a second reference voltage signal Vr+. Wherein, the level of the second reference voltage signal Vr+ is higher than that of the first reference voltage signal Vr−, and the level of the feedback signal FB represents the power consumption of the LED module 150 .

When the level of the feedback signal FB is lower than the first reference voltage signal Vr-, the first comparator 106 outputs a high level signal to turn on the first switch 114, and the first comparator 106 outputs a low level signal to turn off the second switch 114. Switch 115. At this time, the capacitor 116 is charged by the first charging unit so that the voltage of the capacitor 116 rises, and the duty cycle of the pulse width modulation signal S2 of the pulse width modulator 120 rises. When the level of the feedback signal FB is higher than the second reference voltage signal Vr+, the first comparator 106 outputs a low level signal to turn off the first switch 114, and the second comparator 108 outputs a high level signal to turn on the second Switch 115. At this time, the capacitor 116 is discharged by the first discharge unit so that the voltage of the capacitor 116 drops, so that the duty cycle of the pulse width modulation signal S2 of the pulse width modulator 120 drops. When the level of the feedback signal FB is between the first reference voltage signal Vr- and the second reference voltage signal Vr+, both the first comparator 106 and the second comparator 108 output low-level signals to maintain the voltage of the capacitor 116 constant. As mentioned above, the feedback signal FB will be controlled within a predetermined range to stabilize the power consumption of the LED module 150 (ie, the output current of the power conversion circuit 160 ).

In addition to the DC-to-DC boost conversion circuit in the above-mentioned embodiments, other conversion circuits with DC voltage output functions can be used in the light-emitting diode driving circuit of the present invention, such as: DC-to-DC step-down circuit, flyback conversion circuit, positive excited conversion circuit, etc. The flyback conversion circuit is described below.

Please refer to FIG. 3 . FIG. 3 is a schematic circuit diagram of a LED driving circuit according to a third preferred embodiment of the present invention. The LED driving circuit includes a control circuit 200 and a power conversion circuit 260 for driving an LED module 250 . The light emitting diode module 250 has a plurality of light emitting diode strings and these light emitting diode strings are connected in parallel with each other. The power conversion circuit 260 is connected to an AC input power VAC through a bridge rectifier BD to convert the power of the AC input power VAC according to a control signal Sc to drive the LED module 250 to emit light. In this implementation, the power conversion circuit 260 is a flyback conversion circuit, including a transformer T, a transistor switch SW, a rectifier diode D and an output capacitor C. One end of the primary coil of the transformer T is connected to the AC input power VAC, and the other end is connected to one end of the transistor switch SW, and the other end of the transistor switch SW is grounded through a current detection resistor. One end of the output capacitor C is connected to the secondary coil of the transformer T through a rectifier diode D and the other end is grounded.

In order to ensure that any light emitting diode in the light emitting diode module 250 flows approximately the same current, the light emitting diode driving circuit can add a current balance module 270, which has a plurality of current balance terminals D1-Dn, and is connected to the light emitting diode module 250 one by one. A plurality of LED strings are used to balance the current of the multiple LED strings so that the current of each LED string is stabilized at a predetermined current value. Since the driving voltage required by each LED string to flow through the predetermined current value is different, the voltage levels of the plurality of current balancing terminals D1 -Dn are different. In order to make the current balance terminals D1-Dn of the current balance module 270 operate normally, that is, to control the flowing current to a predetermined current value, the voltage level of the current balance terminals D1-Dn must be maintained at a minimum operable voltage value. To this end, the present invention can add a first extreme voltage detection circuit 240 connected to multiple current balance terminals D1-Dn, and generate a first feedback signal FB1 according to the lowest potential among the current balance terminals D1-Dn. The first terminal voltage detection circuit 240 may include a plurality of diodes, the cathodes of which are respectively connected to a plurality of current balancing terminals D1-Dn, and the anodes thereof are connected to each other and to a driving power supply VCC through a resistor. In this way, except that the diode corresponding to the current balance end with the lowest potential can conduct forward, the cross-voltage on the other diodes is insufficient to prevent conduction, so that the potential of the first feedback signal FB1 is the lowest potential of the current balance end plus the diode's positive bias.

The control circuit 200 includes a duty cycle adjustment unit 210 , a feedback control unit 212 , a charging unit, a discharging unit and a capacitor 216 . The charging unit has a first current source I1 and a first switch 214 , the first current source I1 is connected to the capacitor 216 through the first switch 214 to provide a charging current to charge the capacitor 216 . The discharge unit has a second current source I2 connected to the capacitor 216 to provide a discharge current to discharge the capacitor 216 . The feedback control unit 212 can be a comparator, the non-inverting end of which receives a first reference voltage signal Vr1 , and the inverting end receives the first feedback signal FB1 to control the first switch 214 to be turned on and off accordingly. The duty cycle adjustment unit 210 includes a pulse width modulator 220 and a driving circuit 230 , and adjusts the duty cycle of an output control signal Sc according to the voltage of the capacitor 216 . The pulse width modulator 220 can be a comparator, its non-inverting terminal receives a ramp signal, and its inverting terminal is connected to the connection capacitor 216 to generate a pulse width modulation signal S2 to the driving circuit 230 accordingly. The driving circuit 230 generates a control signal Sc according to the pulse width modulation signal to control the power conversion circuit 260 to maintain the lowest potential among the current balancing terminals D1 -Dn at a predetermined voltage value. The lower the predetermined voltage value is set, the higher the efficiency of the power conversion circuit 260 to drive the light emitting diode module 250 to emit light.

Since the current balance module 270 has a withstand voltage limit, when any potential of the current balance terminals D1 ˜ Dn is higher than the withstand voltage value, the current balance module 270 will be damaged. For example: when any of the LED strings in the LED module 250 is open, the control circuit 200 continuously increases the output voltage of the power conversion circuit 260 in an attempt to increase the potential of the corresponding current balance terminal to a predetermined voltage value, which will cause other LEDs to The potential of the current balance terminal corresponding to the string is too high; or, when some LEDs in a certain LED string are short-circuited, the voltage across the short-circuited LED string is reduced, resulting in the potential of the current balance terminal corresponding to the LED string being too high. In order to avoid the above problems, a second extreme voltage detection circuit 245 can be added to connect multiple current balance terminals D1-Dn, and generate a second feedback signal FB2 according to the highest potential between the current balance terminals D1-Dn. The second terminal voltage detection circuit 245 may include a plurality of diodes, the anodes of which are respectively connected to a plurality of current balancing terminals D1-Dn correspondingly, and the cathodes thereof are connected to each other and grounded through a resistor. The control circuit 200 further includes an overvoltage comparator 208 , the non-inverting terminal receives the second feedback signal FB2 , and the inverting terminal receives a second reference voltage signal Vr2 . When the potential of the second feedback signal FB2 is higher than the second reference voltage signal Vr2, the overvoltage comparator 208 will output an overvoltage protection signal OVP.

In addition, when the circuit operates normally, the potentials of the plurality of current balancing terminals D1 ˜ Dn can be maintained at or above a predetermined voltage value. When the potential of any current balancing terminal is lower than a predetermined voltage value and cannot rise back to the predetermined voltage value, it means that the circuit is abnormal. However, when the circuit is started up or in the process of dimming, the potentials of the plurality of current balancing terminals D1-Dn will be temporarily lower than the predetermined voltage value. In order to avoid misjudgment and eliminate the abnormality of the above circuit at the same time, a timing circuit 206 can be added to the control circuit 200 to connect to the feedback control unit 212. When the first feedback signal FB1 is continuously lower than the first reference voltage signal Vr1 for a predetermined time period, that is, When the feedback control unit 212 continues to output the high level for a predetermined period of time, the timing circuit 206 outputs an under-low protection signal S1. Of course, the timing circuit 206 can also receive a starting signal or a dimming signal, so as to determine the time point of timing start according to the starting signal or the dimming signal, wherein the starting signal is a signal representing the circuit starts to start. Since the power supply capability of the power conversion circuit varies with the design of different circuits, the length of the required predetermined time period will be different. In order to be compatible with various circuit designs, if the control circuit 200 of the present invention is a single integrated circuit, an additional setting pin can be added to set the above-mentioned predetermined time period through an external resistor or capacitor (not shown).

The control circuit 200 also includes a protection unit 235 connected to the timing circuit 206 , the overvoltage comparator 208 and the driving circuit 230 . When receiving the overvoltage protection signal OVP or receiving the undervoltage protection signal S1 , the driving circuit 230 is controlled to stop generating the control signal Sc to achieve the protection function. In addition, the protection unit 235 can also receive the current detection signal Ise generated by the current detection resistor. When the current detection signal Ise remains at a low level for more than a preset time, it means that the circuit at the input end of the power conversion circuit 260 is open circuited, and the protection unit 235 can also control the driving circuit 230 to stop generating the control signal Sc. Or when the current detection signal Ise exceeds an overcurrent protection value, it means that the circuit at the input end of the power conversion circuit 260 is short-circuited. At this time, the protection unit 235 can output an error signal Fault to notify the previous stage of the circuit to stop supplying power to the LED driver. circuit to avoid short circuits causing more component damage.

Please refer to FIG. 4 . FIG. 4 is a schematic circuit diagram of a LED driving circuit according to a fourth preferred embodiment of the present invention. Comparing this embodiment with the embodiment shown in FIG. 3 , the main differences are that the control circuit 200 is changed from the voltage control mode to the current control mode and the control method for charging and discharging the capacitor 216 is described below.

The control circuit 200 includes a duty cycle adjustment unit 210 , a feedback control unit 212 , a charging unit, a discharging unit and a capacitor 216 . The charging unit has a first current source I1 , a third current source I3 and a third switch 217 . The first current source I1 is connected to the capacitor 216 to provide a basic charging current to charge the capacitor 216 , and the third current source I3 is connected to the capacitor 216 through the third switch 217 to provide a charging current to charge the capacitor 216 . The discharge unit has a second current source I2 and a second switch 215 , and the second current source I2 is connected to the capacitor 216 through the second switch 215 to provide a discharge current to discharge the capacitor 216 . Wherein, the current magnitude of the first current source I1 is smaller than the current magnitudes of the second current source I2 and the third current source I3 . The feedback control unit 212 can be a comparator, the inverting terminal of which receives a first reference voltage signal Vr1 , and the non-inverting terminal receives the first feedback signal FB1 to control the on and off of the second switch 215 accordingly. When the level of the first feedback signal FB1 is lower than the level of the first reference voltage signal Vr1 , the feedback control unit 212 outputs a low level signal to turn off the second switch 215 . At this moment, the first current source I1 charges the capacitor 216 to increase the voltage of the capacitor 216 . When the level of the first feedback signal FB1 is higher than the level of the first reference voltage signal Vr1, the feedback control unit 212 outputs a high level signal to turn on the second switch 215, so that the second current source I2 discharges the capacitor 216, Meanwhile, the first current source I1 charges the capacitor 216 . Since the current of the first current source I1 is smaller than the current of the second current source I2 , the voltage of the capacitor 216 will drop at this moment. The duty cycle adjustment unit 210 includes a pulse width modulator 220 and a driving circuit 230 . The pulse width modulator 220 includes a comparator 222 and an RS flip-flop 224 . The non-inverting terminal of the comparator 222 is connected to the capacitor 216, and the inverting terminal receives the current detection signal Ise. The set terminal S of the RS flip-flop 224 receives a clock signal, and the reset terminal R is connected to the comparator 222 . When the RS flip-flop 224 receives the clock signal at the setting terminal S, the output terminal Q generates a pulse width modulation signal S2 to the driving circuit 230 . The driving circuit 230 receives the PWM signal S2 and a dimming signal DIM to generate a control signal Sc to turn on the transistor switch SW of the power conversion circuit 260 . When the current flowing through the primary coil of the transformer T rises so that the level of the current detection signal Ise is higher than the voltage level of the capacitor 216, the comparator 222 outputs a signal of a high level to reset the RS flip-flop 224. At this time, the driving circuit 230 stops generating the control signal Sc. At this time, the transistor switch SW of the power conversion circuit 260 is turned off, so that the energy stored in the transformer T is transmitted to the secondary coil of the power conversion circuit 260 to provide power to drive the LED module 250 to emit light.

At the beginning of the circuit startup or the dimming process, the voltage of the capacitor 216 can rise rapidly to improve the transient response speed of the control circuit 200 . The control circuit 200 controls the third switch 217 through the transient boost circuit 204 . The transient boost circuit 204 receives the start signal EN and the dimming signal DIM. When the start signal EN is received, the dimming signal DIM changes from the "OFF" state (representing that the LED module 250 stops emitting light) to the "ON" state (representing that the light emitting diode module 250 stops emitting light). 250 light), output a high level signal to turn on the third switch 217, at this time the third current source I3 and the first current source I1 charge the capacitor 216 at the same time, so that the voltage of the capacitor 216 rises rapidly. The transient boost circuit 204 can set a predetermined length of time or disconnect the third switch 217 according to the first feedback signal FB1, that is, the third switch 217 will be turned on for a fixed time and then disconnected; or when the current balance of the current balance module 270 is balanced The third switch 217 is turned off when the lowest level among the terminals D1-Dn reaches a predetermined level.

In addition, the non-inverting end of the overvoltage comparator 208 in this embodiment receives a third feedback signal FB3 to replace the second feedback signal FB2 in the embodiment shown in FIG. 3 . The third feedback signal FB3 is generated by a voltage detection circuit 275 detecting the output voltage of the power conversion circuit 260 . When the output voltage of the power conversion circuit 260 is higher than a predetermined protection value and the level of the third feedback signal FB3 is higher than the level of the second reference voltage Vr2, the overvoltage comparator 208 outputs an overvoltage protection signal OVP to make the protection unit 235 controls the drive circuit 230 to stop outputting the control signal Sc.

The present invention has been disclosed above with preferred embodiments, but those skilled in the art should understand that the embodiments are only used to describe the present invention, and should not be construed as limiting the scope of the present invention. It should be noted that all changes and substitutions equivalent to this embodiment should be included in the scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the scope defined in the claims of the present application.

Claims (11)

1. a control circuit, in order to control a power-switching circuit, to stablize the output of this power-switching circuit, this control circuit comprises:

One electric capacity;

One charhing unit, has one first current source and connects this electric capacity, in order to this electric capacity is charged;

One discharge cell, connects this electric capacity, in order to this electric capacity is discharged;

One feedback control unit, according to a feedback signal that represents this output state to control this charhing unit to this capacitor charging;

One work period adjustment unit, in order to produce a control signal, and adjusts the work period of this control signal according to the voltage of this electric capacity;

And

One protected location; when the level of this feedback signal is during lower than one first protection value or when the level of this feedback signal continues to reach a predetermined period of time lower than this first protection value, this protected location produces a guard signal makes this work period adjustment unit stop exporting this control signal.

2. control circuit according to claim 1, wherein this charhing unit has one first switch and is connected between this first current source and this electric capacity, this feedback control unit has a comparator, and this comparator is according to this feedback signal and a reference voltage signal control this first switch conduction and disconnection.

3. control circuit according to claim 1, wherein this charhing unit has one first switch and is connected between this first current source and this electric capacity, this discharge cell has a second switch and one second current source, this second switch is connected between this second current source and this electric capacity, and this feedback control unit is according to conducting and the disconnection of this first switch of this feedback signal control and this second switch.

4. control circuit according to claim 1, wherein this charhing unit has one the 3rd switch and one the 3rd current source, the 3rd switch is connected between the 3rd current source and this electric capacity, this discharge cell has a second switch and one second current source, this second switch is connected between this second current source and this electric capacity, this feedback control unit is according to this feedback signal to control conducting and the disconnection of the 3rd switch and this second switch, and wherein the size of current of the 3rd current source is greater than the size of current of this first current source.

5. according to the arbitrary described control circuit of claim 1-4; wherein when the level of this feedback signal during higher than one second protection value maybe when an output voltage of this power-switching circuit is during higher than a 3rd protection value, this protected location produces a guard signal makes this work period adjustment unit stop exporting this control signal.

6. a LED driving circuit, in order to drive a light-emitting diode (LED) module, this light-emitting diode (LED) module has multiple light-emitting diodes pipe strings and this light-emitting diodes pipe string is connected in parallel to each other, and this LED driving circuit comprises:

One current balance module, has the plurality of light-emitting diodes pipe string of the corresponding connection of multiple current balance type ends, in order to the electric current of the plurality of light-emitting diodes pipe string of balance;

One first extreme voltage detecting circuit, connects the plurality of current balance type end, and produces one first feedback signal according to potential minimum between the plurality of current balance type end;

One power-switching circuit, connects an input power, to drive this light-emitting diode (LED) module luminous the electric power conversion of this input power according to a control signal;

And

One control circuit, produces this control signal according to this first feedback signal, and this control circuit comprises: an electric capacity; One charhing unit, has one first current source and connects this electric capacity, in order to this electric capacity is charged; One discharge cell, connects this electric capacity, in order to this electric capacity is discharged; One feedback control unit, according to this first feedback signal to control this charhing unit to this capacitor charging;

One work period adjustment unit, in order to produce a control signal and to adjust work period of this control signal according to the voltage of this electric capacity;

And,

One protected location; when the level of this first feedback signal during lower than one first protection value maybe in the time that the level of this first feedback signal continues to reach a predetermined period of time lower than this first protection value, this protected location produces a guard signal makes this control circuit stop exporting this control signal.

7. LED driving circuit according to claim 6, wherein this charhing unit has one first switch and is connected between this first current source and this electric capacity, this feedback control unit has a comparator, this comparator according to this first feedback signal and a reference voltage signal to control this first switch conduction and disconnection.

8. LED driving circuit according to claim 6, wherein this charhing unit has one first switch and is connected between this first current source and this electric capacity, this discharge cell has a second switch and one second current source, this second switch is connected between this second current source and this electric capacity, and this feedback control unit is according to conducting and the disconnection of this first switch of this feedback signal control and this second switch.

9. LED driving circuit according to claim 6, wherein this charhing unit has one the 3rd switch and one the 3rd current source, the 3rd switch is connected between the 3rd current source and this electric capacity, this discharge cell has a second switch and one second current source, this second switch is connected between this second current source and this electric capacity, this feedback control unit according to this first feedback signal and a reference voltage signal to control conducting and the disconnection of the 3rd switch and this second switch, and the size of current of the 3rd current source is greater than the size of current of this first current source.

10. LED driving circuit according to claim 6; also comprise one second extreme voltage detecting circuit; connect the plurality of current balance type end; and produce one second feedback signal according to maximum potential between the plurality of current balance type end, wherein this control circuit stops exporting this control signal during higher than an overvoltage protection value when this second feedback signal.

11. according to the arbitrary described LED driving circuit of claim 6-10; wherein this protected location connects this power-switching circuit; when an output voltage of this power-switching circuit is during higher than one second protection value, this protected location produces a guard signal makes this control circuit stop exporting this control signal.

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