JP2012080019A - Light-emitting element drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-emitting element drive circuit in which the charges stored as a parasitic capacitance for a light-emitting element portion, having a plurality of light-emitting elements connected in series so that a current flows in one direction, can be discharged suitably.SOLUTION: The light-emitting element drive circuit 10 comprises a current drive circuit 30 connected to the cathode terminal of a light-emitting element portion 100, having a plurality of light-emitting elements connected in series so that a current flows in one direction, and driving the light-emitting element portion 100 to emit light within a predetermined emission period, and a discharge circuit 40 which discharges the charges, stored as a parasitic capacitance for the light-emitting element portion 100, from the cathode terminal side to the ground side within a predetermined discharge period starting from the start time of the emitting period.

Description

  The present invention relates to a light-emitting element driving circuit, and more particularly, to a light-emitting element driving circuit that current-drives the light-emitting element portion so that a light-emitting element portion having a plurality of light-emitting elements emits light.

  Currently, light emitting elements such as LEDs are used in various electronic devices and the like, and may be used, for example, as a backlight of a display unit of a liquid crystal television. In this case, a light emitting element portion in which a plurality of light emitting elements are connected in series may be configured, and the plurality of light emitting elements may be caused to emit light by flowing a relatively large current through the light emitting element portion.

  As a technique related to the present invention, for example, in Patent Document 1, as a light emitting element driving circuit, illuminance information from an illuminance sensor is acquired, brightness is determined, the determination result is output, and brightness change information is also provided. The brightness determination unit to be output, the brightness setting based on the brightness determination result of the brightness determination unit, the brightness setting information that outputs the brightness setting information and the brightness change information, and the brightness setting unit And a light emitting element driving unit that drives the light emitting element with a current having a current value corresponding to the luminance setting information. The light emitting element driving circuit further detects a terminal voltage of one terminal of the light emitting element and compares it with a predetermined voltage, and detects at least one of brightness change information or brightness change information. Based on the output of the comparison unit, a boost determination unit that determines whether or not to boost the terminal voltage of the other side terminal of the light emitting element, and when the boost determination unit determines to boost, the other side terminal of the light emitting element A boosting circuit unit that boosts the terminal voltage and does not boost the terminal voltage of the other terminal of the light emitting element when it is determined by the boosting determination unit that boosting is not performed.

JP 2010-67749 A

  By the way, when light is caused to flow through the light emitting element portion, charges may be accumulated as parasitic capacitance between the anode terminal and the cathode terminal of each light emitting element. Then, when the light emission of the light emitting element unit starts, the charge accumulated as the parasitic capacitance flows to the cathode terminal side.For example, the feedback voltage is received from the cathode terminal side of the light emitting element unit, and the voltage is boosted. When the boosted voltage is supplied to the anode terminal of the light emitting element portion, there is a problem that the charge is superimposed as noise on the feedback voltage, and the feedback loop becomes unstable.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a light emitting element driving circuit capable of suitably discharging charges accumulated as parasitic capacitance to a light emitting element portion having a plurality of light emitting elements connected in series so that current flows in one direction. Is to provide.

  A light emitting element driving circuit according to the present invention is connected to a cathode terminal of a light emitting element unit having a plurality of light emitting elements connected in series so that current flows in one direction, and within a predetermined light emission period, Accumulated as a parasitic capacitance to the light emitting element part within a predetermined discharge period calculated from the start time of the light emitting period, and a current driving circuit part that drives the light emitting element part to emit light so that the light emitting element part emits light And a discharge circuit section for discharging the generated charge from the cathode terminal side to the ground side.

  According to the above configuration, the charge accumulated as the parasitic capacitance of the light emitting element portion can be discharged from the cathode terminal side to the ground side within a predetermined discharge period that is calculated from the start time of the light emission period. it can.

In an embodiment concerning the present invention, it is a figure showing a light emitting element drive circuit. In an embodiment concerning the present invention, it is a figure showing a pulse signal etc. inputted and outputted to a control part. In embodiment which concerns on this invention, it is a figure which shows each element of the switching process part for discharge circuits. 6 is a timing chart showing how a discharge circuit pulse signal is generated in the discharge circuit switching processing section in the embodiment of the present invention.

  Embodiments according to the present invention will be described below in detail with reference to the drawings. In the following description, it is assumed that the number of light-emitting elements constituting the light-emitting element unit is four. However, the number of light-emitting elements may be increased or decreased, for example, the back of a display unit of a large-sized liquid crystal television. When used as a light, it may be constituted by using several tens of light emitting elements. In the following description, it is assumed that the control unit is included as a component of the light emitting element driving circuit, but the control unit is not a component of the light emitting element driving circuit but an external component of the light emitting element driving circuit. Also good.

  Also, in the following, in all the drawings, the same symbols are attached to the same elements, and the duplicate description is omitted. In the description in the text, the symbols described before are used as necessary.

  FIG. 1 is a diagram showing a light emitting element driving circuit 10. The light emitting element driving circuit 10 includes a booster circuit unit 20, a current driving circuit unit 30, a discharge circuit unit 40, and a control unit 50. The light emitting element driving circuit 10 is a circuit that drives the light emitting element unit 100 with current. First, the light emitting element unit 100 will be described, and then each configuration of the light emitting element driving circuit 10 will be specifically described.

  The light emitting element unit 100 includes a light emitting element 100a, a light emitting element 100b, a light emitting element 100c, and a light emitting element 100d. The light emitting elements 100a, 100b, 100c, and 100d are circuit elements that emit light when a forward voltage is applied to the anode terminal (anode) with respect to the cathode terminal (cathode). The anode terminal of the light emitting element 100a is connected to the terminal 3, and the cathode terminal of the light emitting element 100a is connected to the anode terminal of the light emitting element 100b. The anode terminal of the light emitting element 100b is connected to the cathode terminal of the light emitting element 100a, and the cathode terminal of the light emitting element 100b is connected to the anode terminal of the light emitting element 100c. The anode terminal of the light emitting element 100c is connected to the cathode terminal of the light emitting element 100b, and the cathode terminal of the light emitting element 100c is connected to the anode terminal of the light emitting element 100d. Furthermore, the anode terminal of the light emitting element 100d is connected to the cathode terminal of the light emitting element 100c, and the cathode terminal of the light emitting element 100d is connected to the terminal 5. That is, the light-emitting element 100a, the light-emitting element 100b, the light-emitting element 100c, and the light-emitting element 100d are connected in series, and the luminance can be changed by changing the value of a current flowing through each light-emitting element. Hereinafter, the anode terminal of the light emitting element 100a will be described as the anode terminal of the light emitting element unit 100, and the cathode terminal of the light emitting element 100d will be described as the cathode terminal of the light emitting element unit 100.

  The step-up circuit unit 20 includes a step-up error amplifier 201, a feedback switching circuit 202, a step-up PWM circuit 203, a step-up coil 204, a step-up transistor 205, a step-up diode 206, a step-up capacitor 207, And a phase compensation capacitor 208. The booster circuit unit 20 has a function of receiving the voltage of the cathode terminal of the light emitting element unit 100 as a feedback voltage, performing necessary boosting, and supplying the boosted voltage to the anode terminal of the light emitting element unit 100. The step-up circuit unit 20 is electrically connected to the connection point of the driving circuit transistor 302 and the driving circuit resistor element 304 of the current driving circuit unit 30, the control unit 50, and the anode terminal of the light emitting element unit 100 via the terminal 3. It is connected.

  The step-up error amplifier 201 is a Gm amplifier that compares the magnitudes of two input voltages and amplifies and outputs the difference between the input voltages. The reference power supply 201 a is input to the plus side input terminal of the boost error amplifier 201. The reference power supply 201a is a power supply that outputs a cathode terminal reference voltage (for example, 0.5 V) for maintaining the voltage of the cathode terminal of the light emitting element unit 100 at a predetermined voltage. The negative side input terminal of the boosting error amplifier 201 is connected to a connection point between the driving circuit transistor 302 and the driving circuit resistance element 304 of the current driving circuit unit 30 in order to receive the feedback voltage from the light emitting element unit 100. ing. The output of the boost error amplifier 201 is input to the first switching terminal 202 a of the feedback switching circuit 202. The boost error amplifier 201 compares the feedback voltage input from the light emitting element unit 100 with the reference voltage input from the reference power supply 201a, and a voltage deviation obtained by amplifying the difference between the voltages is a first switching terminal 202a. Is output for.

  The feedback switching circuit 202 includes a switch body 202c connected to the input terminal of the boosting PWM circuit 203, a first switching terminal 202a connected to the boosting error amplifier 201, and a second switching terminal that is an open terminal. 202b. The feedback switching circuit 202 is controlled to be switched by the control unit 50.

  The step-up PWM circuit 203 is one of modulation methods, and is a circuit that modulates by changing the duty ratio of the pulse signal. Specifically, when the switch body 202c is connected to the first switching terminal 202a, a voltage deviation as a comparison result by the boosting error amplifier 201 is received as an input, and the pulse signal based on the voltage deviation is received. Change the duty ratio. Then, it has a function of performing switching control of the boosting transistor 205 by a pulse signal based on the voltage deviation. When the switch body 202c is connected to the second switching terminal 202b, which is an open terminal, the terminal voltage of the cathode terminal of the light emitting element 100 is not fed back to the booster circuit 20 and is used as a booster PWM circuit. The input voltage 203 is held by the capacitor 208. In FIG. 1, the booster circuit unit 20 continues the boosting operation, but the booster circuit unit may be stopped.

  The boosting transistor 205 is an n-channel MOS transistor that controls the current between the source and drain terminals based on the principle of applying a voltage to the gate terminal and providing a gate (gate) for the flow of electrons or holes by the electric field of the channel. The boosting transistor 205 is subjected to switching control by applying a pulse signal output from the boosting PWM circuit 203 to the gate terminal. The boosting transistor 205 has a gate terminal electrically connected to the output of the boosting PWM circuit 203, a drain terminal electrically connected to the other end of the boosting coil 204 and the anode terminal of the boosting diode 206, and a source terminal. Is connected to the ground 2 and grounded.

  The boosting coil 204 has one end connected to the input power supply voltage 1 and the other end connected to the drain terminal of the boosting transistor 205 and the anode terminal of the boosting diode 206. The boosting coil 204 is in a state where the input power supply voltage 1 is applied when the boosting transistor 205 is turned on, and electromagnetic energy is accumulated.

  The step-up diode 206 is a circuit element having a rectifying action (an action that allows a current to flow only in a certain direction). In the boosting diode 206, when the boosting transistor 205 is turned off, the boosting coil 204 in which electromagnetic energy is stored functions as a voltage source, and a current is supplied to the load side via the boosting diode 206. Will be washed away. The boosting diode 206 has an anode terminal electrically connected to the other end of the boosting coil 204 and the drain terminal of the boosting transistor 205, and a cathode terminal connected to the positive terminal of the boosting capacitor 207.

  The boosting capacitor 207 is a circuit element that stores and discharges electric charges (electric energy) by electrostatic capacity. The boosting capacitor 207 has a function of accumulating charges flowing from the boosting coil 204 when the boosting transistor 205 is turned off. The boosting capacitor 207 is electrically connected to the cathode terminal of the boosting diode 206 and the anode terminal of the light emitting element unit 100 at the positive electrode side terminal and to the ground 2 by connecting the negative electrode side terminal to the ground 2.

  The phase compensation capacitor 208 is a capacitive element whose positive terminal is connected to the switch body 202c and the input of the boosting PWM circuit 203 and whose negative terminal is connected to the ground 2 and grounded. The phase compensation capacitor 208 has a function of performing phase compensation of a feedback loop when the terminal voltage of the cathode terminal of the light emitting element unit 100 is fed back to the booster circuit unit 20.

  The current drive circuit unit 30 is a circuit that drives the light emitting element unit 100 with a predetermined drive current. The current drive circuit unit 30 includes a drive circuit transistor 302 and a drive circuit resistance element 304.

  The driver circuit transistor 302 is an n-channel MOS transistor that controls the current between the source and drain terminals based on the principle that a voltage is applied to the gate terminal and a gate (gate) is provided for the flow of electrons or holes by the electric field of the channel. . The driving circuit transistor 302 is subjected to switching control by applying a driving circuit pulse signal output from the control unit 50 to the gate terminal. The drive circuit transistor 302 has a gate terminal electrically connected to the control unit 50, a drain terminal electrically connected to the cathode terminal of the light emitting element unit 100 via the terminal 5, and a source terminal connected to the drive circuit resistance element. One end of 304 and the drain terminal of the discharge circuit transistor 402 are connected to ground.

  One end of the drive circuit resistance element 304 is connected to the source terminal of the drive circuit transistor 302 and the other end is connected to the ground 2 and grounded. Note that the drive circuit resistance element 304 has a resistance value set so that the current flowing through the light emitting element portion 100 becomes an allowable maximum current when the drive circuit transistor 302 is turned on.

  The discharge circuit unit 40 is a circuit for discharging charges accumulated as parasitic capacitance to the light emitting element unit 100 to the ground 2 side. The discharge circuit unit 40 includes a discharge circuit transistor 402 and a discharge circuit resistance element 404.

  The discharge circuit transistor 402 is an n-channel MOS transistor that controls the current between the source and drain terminals based on the principle of applying a voltage to the gate terminal and providing a gate (gate) for the flow of electrons or holes by the electric field of the channel. . The discharge circuit transistor 402 is subjected to switching control by applying the discharge circuit pulse signal output from the control unit 50 to the gate terminal. The discharge circuit transistor 402 has a gate terminal electrically connected to the control unit 50, a drain terminal electrically connected to the source terminal of the drive circuit transistor 302 and one end of the drive circuit resistance element 304, and a source terminal Is connected to one end of the discharge circuit resistance element 404. Note that the on-resistances of the discharge circuit transistor 402 and the drive circuit transistor 302 have very small resistance values as compared with the drive circuit resistance element 304.

  The discharge circuit resistance element 404 has one end connected to the source terminal of the discharge circuit transistor 402 and the other end connected to the ground 2 and grounded. The discharge circuit resistance element 404 has a resistance value smaller than the resistance value of the drive circuit resistance element 304, and discharges the charge accumulated as parasitic capacitance in the light emitting element portion 100. In other words, the discharge circuit resistance element 404 is pulled out. Therefore, a suitable resistance value is set.

  The control unit 50 includes a feedback switching processing unit 502, a driving circuit switching processing unit 504, and a discharging circuit switching processing unit 506. FIG. 2 is a diagram showing pulse signals and the like input / output to / from the control unit 50.

  The feedback switching processing unit 502 has a function of performing switching control of the feedback switching circuit 202 based on a feedback loop switching pulse signal (see FIG. 2) input from the outside. Specifically, during the High period of the feedback loop switching pulse signal, switching is performed so that the connection destination of the switch body 202c of the feedback switching circuit 202 becomes the first switching terminal 202a. Then, during the low period of the feedback loop switching pulse signal, switching is performed so that the connection destination of the switch body 202c of the feedback switching circuit 202 is the second switching terminal 202b. That is, during the High period of the feedback loop switching pulse signal, the terminal voltage of the cathode terminal of the light emitting element unit 100 is fed back to the boosting circuit unit 20 and the boosting circuit unit 20 performs boosting, but the Low period of the feedback loop switching pulse signal is The boosting operation of the booster circuit unit 20 is stopped without the terminal voltage of the cathode terminal of the light emitting element unit 100 being fed back to the booster circuit unit 20. Here, the High period of the feedback loop switching pulse signal is referred to as a feedback period. Note that the feedback loop switching pulse signal preferably has a timing relationship after the High period of the discharge circuit pulse signal ends, in other words, the High period after the discharge period ends.

  The driving circuit switching processing unit 504 has a function of performing switching control of the driving circuit transistor 302 based on a driving circuit pulse signal (see FIG. 2) input from the outside. Specifically, the driving circuit transistor 302 is turned on during the High period of the driving circuit pulse signal, and the driving circuit transistor 302 is turned off during the Low period of the driving circuit pulse signal. That is, during the High period of the driving circuit pulse signal, current flows through the light emitting elements 100a, 100b, 100c, and 100d of the light emitting element unit 100, and each light emitting element emits light. However, during the Low period of the driving circuit pulse signal, light emission occurs. The current does not flow through the light emitting elements 100a, 100b, 100c, and 100d of the element unit 100, and each light emitting element does not emit light. Note that the light emission luminance of the light emitting elements 100a, 100b, 100c, and 100d can be changed by changing the length of the High period of the pulse signal for the drive circuit. Here, the High period of the drive circuit pulse signal is referred to as the light emission period of the light emitting element portion 100.

  The discharge circuit switching processing unit 506 has a function of generating the discharge circuit pulse signal shown in FIG. 2 and performing switching control of the discharge circuit transistor 402 based on the discharge circuit pulse signal. FIG. 3 is a diagram showing each element of the discharge circuit switching processing unit 506. FIG. 4 is a timing chart showing how a discharge circuit pulse signal is generated in the discharge circuit switching processing unit 506. The discharge circuit switching processing unit 506 includes a resistance element 506a, a capacitor 506b, an inverter circuit 506c, and an AND circuit 506d.

  The resistance element 506a is a resistance element connected to the positive terminal of the capacitor 506b and the input terminal of the inverter circuit 506c at one end thereof.

  The capacitor 506b is a capacitance element whose positive terminal is connected to the other end of the resistance element 506a and the input terminal of the inverter circuit 506c, and whose negative terminal is connected to the ground 2 and grounded.

  The inverter circuit 506c is an inverting circuit whose input terminal is connected to the other end of the resistance element 506a and the positive terminal of the capacitor 506b, and whose output terminal is connected to the first input terminal of the AND circuit 506d.

  The AND circuit 506d has a first input terminal connected to the output terminal of the inverter circuit 506c, a second input terminal to which an external drive circuit pulse signal is input, and an output terminal for switching the discharge circuit transistor 402. It is a logical product circuit that outputs a signal as a discharge circuit pulse signal for performing control.

  The signal 5062 is a drive circuit pulse signal (the same pulse signal as the drive circuit pulse signal in FIG. 2) input to one end of the resistance element 506a and the second input terminal of the AND circuit 506d.

  The signal 5064 is a signal input to the inverter circuit 506c, and is a time constant function signal that changes according to a time constant determined by the values of the resistance element 506a and the capacitor 506b.

  The signal 5066 is a signal output from the inverter circuit 506c and input to the first input terminal of the AND circuit 506d. The signal 5066 is high when the input (signal 5064) of the inverter circuit 506c is smaller than the predetermined threshold B, and is low when the input (signal 5064) of the inverter circuit 506c is larger than the predetermined threshold B. is there.

  A signal 5068 is a discharge circuit pulse signal output from the AND circuit 506d (the same pulse signal as the discharge circuit pulse signal in FIG. 2). In the High period, the discharge circuit transistor 402 is turned on, and in the Low period, The discharge circuit transistor 402 is turned off. The High period of the discharge circuit pulse signal is called a discharge period.

  Here, the resistance element 506a and the capacitor 506b function as a time constant circuit whose value is set in advance in order to generate a discharge period necessary for discharging the charge accumulated as parasitic capacitance with respect to the light emitting element portion 100. The inverter circuit 506c and the AND circuit 506d function as a pulse generation circuit that generates a discharge circuit pulse signal based on the time constant function signal output by the resistance element 506a and the capacitor 506b.

  Next, the operation of the light emitting element driving circuit 10 having the above configuration will be described. The light emitting element driving circuit 10 performs on / off control of the driving circuit transistor 302 in accordance with an external driving circuit pulse signal. Specifically, during the High period (light emission period) of the drive circuit pulse signal, the drive circuit transistor 302 is turned on to allow light emission by causing a constant current to flow through the light emitting element portion 100, and during the Low period of the drive circuit pulse signal. The driver circuit transistor 302 is turned off to stop the light emitting element unit 100 from emitting light.

  Then, the light emitting element driving circuit 10 performs switching so that the voltage of the cathode terminal of the light emitting element unit 100 becomes a predetermined voltage by an external feedback switching pulse signal. Specifically, during the High period (feedback period) of the feedback switching pulse signal, the connection destination of the switch body 202c of the feedback switching circuit 202 is switched to become the first switching terminal 202a. Is fed back to the booster circuit unit 20, and the booster circuit unit 20 performs boosting. The low period of the feedback loop switching pulse signal is switched so that the connection destination of the switch main body 202c of the feedback switching circuit 202 becomes the second switching terminal 202b that is an open terminal. Is not fed back to the booster circuit unit 20, and the input voltage of the booster PWM circuit 203 is held by the capacitor 208. In FIG. 1, the booster circuit unit 20 continues the boosting operation, but the booster circuit unit may be stopped. Accordingly, by setting the voltage of the cathode terminal of the light emitting element unit 100 to a predetermined voltage during the feedback period, the voltage can be stabilized even when the light emitting element unit 100 emits light.

  As described above, when the light emitting element unit 100 is caused to emit light by the light emitting element driving circuit 10, for example, a charge is generated as a parasitic capacitance between the anode terminal and the cathode terminal of the light emitting elements 100a, 100b, 100c, and 100d. Accumulated. However, according to the configuration of the light emitting element drive circuit 10, the discharge circuit transistor 402 is turned on during the High period (discharge period) that starts in synchronization with the time when the High period of the drive circuit pulse signal starts. At this time, since the resistance value of the discharge circuit resistance element 402 is smaller than the resistance value of the drive circuit resistance element 304, the discharge circuit unit 40 has the charge accumulated as the parasitic capacitance of each light emitting element on the ground 2 side. In other words, the discharge circuit section 40 functions as a path for discharging the charge accumulated as the parasitic capacitance. Thus, during the High period (discharge period) of the discharge circuit pulse signal, the charge accumulated as the parasitic capacitance of each light emitting element is drawn out to the ground 2 side, so that it is indicated by a dotted line as shown in FIG. The feedback voltage shaped without superimposing the generated noise (refer to region A in FIG. 2) can be ford-backed to the booster circuit unit 20. Therefore, higher stability of the feedback loop of the light emitting element driving circuit 10 can be maintained.

  DESCRIPTION OF SYMBOLS 1 Input power supply voltage, 2 ground, 3, 5 terminal, 10 Light emitting element drive circuit, 20 Boost circuit part, 30 Current drive circuit part, 40 Discharge circuit part, 50 Control part, 100 Light emitting element part, 100a, 100b, 100c, 100d light emitting element, 201 boosting error amplifier, 201a reference power supply, 202 feedback switching circuit, 202a first switching terminal, 202b second switching terminal, 202c switch body, 203 boosting PWM circuit, 204 boosting coil, 205 boosting Transistor, 206 boosting diode, 207 boosting capacitor, 208 phase compensation capacitor, 302 driving circuit transistor, 304 driving circuit resistance element, 402 discharging circuit transistor, 404 discharging circuit resistance element, 502 feedback switching processing unit, 504 Switching processing unit for driving circuit, 506 Switching processing unit for discharging circuit, 506a Resistance element, 506b Capacitor, 506c Inverter circuit.

Claims (5)

The light emitting element unit is connected to a cathode terminal of a light emitting element unit having a plurality of light emitting elements connected in series so that a current flows in one direction, and the light emitting element unit emits light within a predetermined light emitting period. A current driving circuit unit for driving the light emitting element unit with current;
A discharge circuit section for discharging a charge accumulated as a parasitic capacitance to the light emitting element section from the cathode terminal side to the ground side within a predetermined discharge period calculated from the start time of the light emission period;
A light-emitting element driving circuit comprising: In the light emitting element drive circuit according to claim 1,
A booster circuit unit that receives a feedback voltage on the cathode terminal side so that the cathode terminal has a predetermined voltage and supplies a boosted voltage boosted based on the feedback voltage to the anode terminal of the light emitting element unit A light-emitting element driving circuit comprising: In the light emitting element drive circuit according to claim 1 or 2,
A time constant circuit that outputs a value corresponding to a time constant function that changes with a predetermined time constant from an initial value at the start time of the light emission period;
A discharge period generation circuit that generates a period between the start time of the light emission period and the time when the output value of the time constant circuit exceeds a predetermined threshold as the discharge period;
A light-emitting element driving circuit comprising: In the light emitting element drive circuit of any one of Claims 1-3,
The light emitting element drive circuit according to claim 1, wherein a circuit impedance of the discharge circuit unit is smaller than a circuit impedance of the current drive circuit unit. In the light emitting element drive circuit according to claim 4,
The current drive circuit unit is
A drive circuit switch circuit having one end connected to the cathode terminal and turned on during the light emission period and turned off during the light emission period;
A driving circuit resistance element having one end connected to the other end of the driving circuit switch circuit and the other end grounded;
Have
The discharge circuit section is
A discharge circuit switch circuit, one end of which is connected between the cathode terminal and one end of the drive circuit resistance element, and is turned on during the discharge period and turned off outside the discharge period;
One end is connected to the other end of the discharge circuit switch circuit, the other end is grounded, and the resistance element for the discharge circuit includes a resistance value smaller than the resistance value of the resistance element for the drive circuit;
A light emitting element driving circuit comprising:

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