Backlight source driving circuit

Abstract

The utility model relates to the technical field of backlight power supplies, in order to solve the technical problem that illumination stability is affected by pre-stage interference of a backlight circuit, the utility model discloses a backlight driving circuit, which comprises a backlight controller U10 and a first group of driving circuits, the first group of driving circuits comprises a transformer T2, a PMOS (P-channel Metal Oxide Semiconductor) tube Q22 and an NMOS (N-channel Metal Oxide Semiconductor) tube Q13, the grid electrode of the PMOS tube Q22 and the grid electrode of the NMOS tube Q13 are respectively connected with the driving signal output end of the backlight controller U10, the source electrode of the PMOS tube Q22 is connected with the drain electrode of the NMOS tube Q13, and the drain electrode of the PMOS tube Q22 is connected with the power supply VCC1; a first end of a primary side coil of the transformer T2 is connected with a drain electrode of the NMOS tube Q13 through a capacitor C61, and a second end of the primary side coil of the transformer T2 is grounded; the first end of a secondary side coil of the transformer T2 outputs a first power source positive electrode V1 + for supplying power to a lamp panel through a fast recovery diode D20, the transformer T2 achieves front-stage and rear-stage isolation, rectification is conducted through the fast recovery diode, and through high-frequency low-resistance electrolytic filtering, the response speed is increased, and interference is reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of backlight power supply, in particular to a backlight source driving circuit. Background Art

[0002] The backlight driver circuit is a key circuit used in display devices such as monitors to provide backlight brightness and stability.

[0003] The Chinese utility model patent with the publication (announcement) number CN202634777U discloses an LED backlight source driving circuit. Figure 1 According to paragraph

[0020] of the specification, the flat-panel TV LED backlight source driving circuit of the utility model embodiment includes a main circuit and a control circuit, the main circuit includes a DC input circuit, an energy storage inductor L5, a switch tube Q29, an RC stress absorption circuit and an output rectifier filter circuit, and the output rectifier filter circuit includes a rectifier diode D14 and filter capacitors C32 and EC18. The input end and the output end are isolated by the energy storage inductor L5 and the rectifier diode D14, and the isolation effect is poor, which easily causes the influence of the previous stage on the next stage.

[0004] The interference signal at the input end may propagate to the output end through the energy storage inductor L5 and the rectifier diode D14, affecting the stable operation of the LED backlight source. The influence of the front stage on the rear stage may cause the output voltage to fluctuate, thereby affecting the brightness stability of the LED and even causing damage to the LED. Poor isolation may lead to increased energy loss and affect the efficiency of the overall circuit. If the interference signal of the front stage propagates to the rear stage, it may have an excessive impact on the rear stage circuit, causing damage to the circuit components. Utility Model Content

[0005] The utility model aims to provide a backlight source driving circuit to solve the technical problem of affecting lighting stability caused by the front-stage interference of the backlight source circuit.

[0006] To achieve the above purpose, the specific technical solution of a backlight source driving circuit of the utility model is as follows:

[0007] A backlight source driving circuit includes a backlight controller U10, and is provided with a first group of driving circuits and a second group of driving circuits connected to a signal output terminal of the backlight controller U10; the first group of driving circuits includes a transformer T2, a PMOS tube Q22 and an NMOS tube Q13, the gates of the PMOS tube Q22 and the NMOS tube Q13 are respectively connected to a first driving signal output terminal and a second driving signal output terminal of the backlight controller U10, the source of the PMOS tube Q22 is connected to a drain of the NMOS tube Q13, and the source of the NMOS tube Q13 is connected to a The drain of the PMOS tube Q22 is connected to the power supply VCC1; the first end of the primary coil of the transformer T2 is connected to the drain of the NMOS tube Q13 through the capacitor C61, and the second end of the primary coil of the transformer T2 is grounded; the first end of the secondary coil of the transformer T2 outputs the first positive power supply V1+ to supply power to the lamp board through the fast recovery diode D20, and the second end of the secondary coil serves as the first negative power supply V1- to supply power to the lamp board, and the cathode of the diode D20 is connected to the second end of the secondary coil through the high-frequency low-resistance electrolytic capacitor C63.

[0008] Furthermore, a first RC circuit is connected in parallel at both ends of the diode D20, and the first RC circuit includes a capacitor C62 and a resistor R78 connected in series, a first end of the capacitor C62 is connected to the anode of the diode D20, a second end of the capacitor C62 is connected to the first end of the resistor R78, and a second end of the resistor R78 is connected to the cathode of the diode D20.

[0009] The capacitor C62 and the resistor R78 in the first RC circuit can effectively filter out high-frequency noise and fluctuations in the circuit, provide a more stable power output, and help reduce flickering and interference of the backlight board. The combination of the capacitor C62 and the resistor R78 can slow down the switching process of the diode D20, reduce the reverse spike of the diode, and help extend the service life of the diode. By optimizing the values ​​of the capacitor C62 and the resistor R78, the circuit output can be made more stable, which helps to improve the brightness stability and uniformity of the backlight board.

[0010] Furthermore, a resistor R79 and a Zener diode Z5 are connected in series between the first positive power supply electrode V1+ and the first negative power supply electrode V1-, the first end of the resistor R79 is connected to the cathode of the diode D20, the second end of the resistor R79 is connected to the cathode of the Zener diode Z5, and the anode of the Zener diode Z5 is connected to the second end of the secondary coil.

[0011] The voltage regulator Z5 can stabilize the output voltage of the circuit at a fixed value. Even if the input voltage fluctuates, the output voltage can remain stable. The voltage regulator Z5 can provide overvoltage protection for the load to prevent damage to the load due to sudden high voltage in the circuit. The voltage regulator Z5 can reduce the voltage noise in the circuit and provide a cleaner and more stable power output.

[0012] Furthermore, a diode D19 is connected in reverse series at both ends of the primary coil of the transformer T2, with a common cathode, and the anode of the diode D19 is connected to both ends of the primary coil. The reverse series design of the diode D19 can prevent the reverse voltage generated by the primary coil of the transformer T2 when the circuit is disconnected, thereby avoiding damage to other circuit components. The diode D19 can suppress the high-frequency noise and interference generated by the transformer T2 during the switching process, and maintain the stability and reliability of the circuit.

[0013] The backlight source driving circuit provided by the utility model has the following advantages:

[0014] The power supply is isolated by a transformer to reduce the impact of the previous stage on the next stage. A fast recovery diode is used in the circuit for rectification, and the power is output to the load through high-frequency low-resistance electrolytic filtering to improve the response speed. In order to further reduce the reverse spike of the diode, an RC circuit is added to the fast recovery diode for filtering.

[0015] In traditional circuits, energy storage inductors and switching tubes are often used to control the brightness of LEDs. However, this circuit uses high-frequency transformers and drive circuits to achieve electrical isolation between the front and rear stages while taking into account efficient energy conversion, which has better energy-saving effects and can control the brightness more stably. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The backlight controller and its peripheral circuit structure diagram provided by the utility model;

[0017] Figure 2 A structural diagram of a dimming circuit provided for the utility model;

[0018] Figure 3 A circuit diagram of a resistance-capacitance grounding network provided by the utility model;

[0019] Figure 4 The structure diagram of the enabling circuit and overvoltage protection circuit provided by the utility model;

[0020] Figure 5 This is a structural diagram of the backlight source driving circuit provided by the utility model. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the utility model more clear, the utility model is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the utility model and are not used to limit the utility model.

[0022] See also Figures 1 to 4The utility model provides a backlight control circuit, which is composed of an internal and external circuit of a power controller U10. It starts working under the control of a main circuit board and outputs four-way driving pulse signals to the backlight driving circuit, and has overvoltage and overcurrent protection functions.

[0023] The first terminal of the backlight controller U10 is a trigger time setting terminal, which is grounded through a capacitor C36;

[0024] The second terminal of the backlight controller U10 is an overvoltage protection detection terminal, which is connected to an overvoltage protection circuit;

[0025] The third terminal of the backlight controller U10 is an enable terminal, which is connected to an enable circuit;

[0026] See also Figure 4 The enabling circuit includes a step-down module U12, a PNP transistor Q14 and an NPN transistor Q12. The base of the transistor Q12 is input with a start-up voltage through a resistor R65. The collector of the transistor Q12 is connected to the power supply VCC1 through resistors R72, R75 and R76. The emitter of the transistor Q12 is grounded through a resistor R67. The base of the transistor Q14 is connected to the collector of the transistor Q12 through resistors R75 and R72. The emitter of the transistor Q14 is connected to the power supply VCC1. The collector of the transistor Q14 is connected to the input end of the step-down module U12. The output end of the step-down module U12 is connected to the enabling end of the backlight controller U10. The ground end of the step-down module U12 is grounded.

[0027] When the base of transistor Q12 is at a low level, transistor Q12 is turned off. The base of transistor Q14 is connected to power supply VCC1 through resistor R76, and the base of transistor Q14 is at a high level, so transistor Q14 is turned on to supply power to step-down module U12, and step-down module U12 outputs power supply VCC2, and power supply VCC2 is supplied to the enable terminal voltage through resistor R68.

[0028] When the base of transistor Q12 is at a high level, transistor Q12 is turned on, pulling down the base voltage of transistor Q14, and the base of transistor Q14 is at a low level, so transistor Q14 is cut off, and the buck module U12 cannot obtain power through the collector of transistor Q14. The buck module U12 stops outputting the power supply VCC2, and there is no corresponding power supply VCC2 to provide the enable terminal voltage through the resistor R68, and the backlight controller U10 cannot be enabled.

[0029] The overvoltage protection circuit includes an NMOS tube Q11, the gate of the NMOS tube Q11 is connected to a first series voltage divider circuit, the first series voltage divider circuit includes a resistor R73 and a resistor R74, the second end of the resistor R74 is grounded, the first end of the resistor R74 is connected to the second end of the resistor R73, the first end of the resistor R73 is connected to the power supply VCC1 through the resistor R75 and the resistor R76 in sequence, the common node of the resistor R74 and the resistor R74 is connected to the gate of the NMOS tube Q11, the source of the NMOS tube Q11 is grounded, and the drain of the NMOS tube Q11 is connected to the enable end of the backlight controller U10.

[0030] When the power supply VCC1 voltage is too high, the first series voltage divider circuit divides a sufficiently high voltage to the gate of the NMOS transistor Q11, causing the NMOS transistor Q11 to be turned on, directly lowering the enable terminal voltage of the backlight controller U10, thereby playing an overvoltage protection role.

[0031] The transistors Q12 and Q14 in the enable circuit form a flexible switch control circuit. Q12 indirectly controls the power supply of the buck module U12 by controlling the switch state of Q14, so that the system can turn on or off the backlight controller U10 as needed, providing flexible power management. The NMOS tube Q11 in the overvoltage protection circuit and the first series voltage divider circuit connected to it are used to monitor the voltage of the power supply VCC1 in real time. When the voltage is too high, the NMOS tube Q11 is turned on to directly lower the enable terminal voltage of the backlight controller U10 to prevent the excessive input voltage from damaging the backlight controller U10 and other circuits, thereby achieving overvoltage protection and improving the safety and reliability of the system. This circuit can not only protect the backlight controller U10 from overvoltage damage, but also improve the overall stability and life of the system through reasonable power management and the use of buck modules. The multi-level protection circuit design ensures that the system can operate safely and stably under various working conditions, reducing the probability of failure caused by power supply fluctuations and overvoltage. In addition, a capacitor C49 is connected in parallel across the resistors R75 and R76 to reduce the probability of circuit malfunction.

[0032] The 4th terminal of the backlight controller U10 is a soft start setting terminal, which is grounded through a capacitor C54;

[0033] The 5th terminal of the backlight controller U10 is a power input terminal, and the grounding resistor R36 is connected to the power supply VCC2 and grounded through the capacitor C53;

[0034] The 6th terminal of the backlight controller U10 is the signal ground terminal, which is grounded;

[0035] The 7th terminal of the backlight controller U10 is a reference voltage output terminal, which is grounded through a capacitor C52 and connected to the 3rd terminal through a diode D21. The anode of the diode D21 is connected to the 3rd terminal, and the cathode of the diode D21 is connected to the 7th terminal.

[0036] The 8th terminal of the backlight controller U10 is the trigger frequency setting terminal and is vacant;

[0037] The 9th terminal of the backlight controller U10 is a current feedback input terminal, which is connected to a feedback circuit;

[0038] The 10th terminal of the backlight controller U10 is a voltage control system compensation terminal, which is grounded through a resistor R50;

[0039] The 11th terminal of the backlight controller U10 is a first driving signal output terminal;

[0040] The 12th terminal of the backlight controller U10 is a second driving signal output terminal;

[0041] The 13th terminal of the backlight controller U10 is a low-frequency pulse width control signal dimming terminal, which is connected to a dimming circuit;

[0042] See also Figure 1 and Figure 2 The dimming circuit includes two integrally formed diodes D50 connected in series. The anode of the diode D50 is connected to the low-frequency pulse width control signal dimming terminal of the backlight controller U10 through a resistor R32 for inputting the signal SG2. The middle common node of the diode D50 is used for inputting the signal SG1. The cathode of the diode D50 is connected to the voltage control system compensation terminal of the backlight controller U10 through a resistor R34.

[0043] It also includes NMOS tube Q5, NMOS tube Q6, NMOS tube Q9 and NMOS tube Q9. The gate of NMOS tube Q5 is used as the input end of the first dimming mode through resistor R50, the source of NMOS tube Q5 is grounded, and the drain of NMOS tube Q5 is connected to the power supply VCC2 through resistor R41. The gate of NMOS tube Q10 is connected to the drain of NMOS tube Q5, the source of NMOS tube Q10 is grounded, and the drain of NMOS tube Q10 is used to output signal SG2. The source of NMOS tube Q6 is grounded, and NMOS tube Q6 is used as the input end of signal E-PWM through resistor R52 for inputting external dimming pulses. The drain of NMOS tube Q6 is connected to the power supply VCC2 through resistor R54. The source of the NMOS tube Q9 is grounded, the gate of the NMOS tube Q9 serves as the input end of the second dimming mode, the drain of the NMOS tube Q9 is used to output the signal SG1 through the diode D11, the anode of the diode D11 is connected to the drain of the NMOS tube Q9, the cathode of the diode D11 is connected to the middle common node of the diode D50, and is also connected to the current feedback input end of the backlight controller U10 through the resistor R55.

[0044] Working principle of dimming circuit:

[0045] The gate of the NMOS tube Q5 is used as the input terminal of the first dimming mode through the resistor R50. When the input signal is at a high level, Q5 is turned on, and its drain voltage drops, driving the NMOS tube Q10 to be turned on, thereby outputting the signal SG2.

[0046] The source of the NMOS tube Q6 is grounded, and the gate thereof serves as the input end of the signal E-PWM through the resistor R52. When the input signal is at a high level, Q6 is turned on and the drain voltage thereof decreases.

[0047] The gate of the NMOS tube Q9 serves as the input terminal of the second dimming mode. When the input signal is at a high level, Q9 is turned on, and its drain outputs a signal SG1 through a diode D11. The cathode of the diode D11 is connected to the middle common node of the diode D50, and is connected to the current feedback input terminal of the backlight controller U10 through a resistor R55.

[0048] When the E-PWM signal is input, the working state of the dimming circuit is directly controlled through Q6.

[0049] The dimming circuit uses multiple NMOS tubes and diodes in cascade, and realizes multiple dimming modes through different input signals, which can efficiently control the brightness of the LED backlight. By using multiple input signals, the circuit can flexibly adjust the backlight brightness according to different needs to meet a variety of application scenarios. The use of low-frequency pulse width dimming signal control makes the dimming process smoother and more accurate, avoiding visual discomfort caused by stroboscopic light.

[0050] The backlight controller U10 adjusts the LED backlight source through the dimming circuit according to different input signals, thereby achieving different dimming effects.

[0051] The 14th terminal of the backlight controller U10 is a low-frequency pulse width control signal dimming duty DC voltage input terminal, which is connected to the I-PWM port through a resistor R38;

[0052] The 15th terminal of the backlight controller U10 is a low-frequency pulse width control signal dimming frequency setting terminal, which is grounded through capacitors C21, C22 and C23 respectively;

[0053] The 16th terminal of the backlight controller U10 is the ground terminal of the internal power tube, which is grounded;

[0054] The 17th terminal of the backlight controller U10 is a trigger and working frequency time setting resistor terminal, which is grounded through a resistor-capacitor grounding network. The grounding network includes a capacitor C27 and a resistor R28 connected in series, a capacitor C24 and a resistor R29 connected in series, a capacitor C25 and a resistor R30 connected in series, and a capacitor C26 and a resistor R31 connected in series. The above capacitors are connected in parallel and in parallel with the resistor R27. One end of the resistor R27 is connected to the 17th terminal, and the other end of the resistor R27 is grounded.

[0055] The purpose of the RC network design is to set the trigger and operating frequency time of the backlight controller. The RC network adjusts the operating frequency of the controller by changing the value of the capacitor and resistor. Each series capacitor and resistor combination can produce a different time constant (τ = RC), which will affect the charge and discharge time of the circuit, thereby changing the operating frequency of the controller.

[0056] Multiple parallel RC combinations can provide more stable and accurate frequency settings. The time constant of each combination is slightly different, which can reduce the error and fluctuation caused by a single RC component and improve the stability and reliability of the overall system.

[0057] The parallel resistor R27 acts as a damper to further stabilize the voltage and current and reduce the impact of noise and fluctuations on the controller triggering and frequency setting.

[0058] The above-mentioned resistor-capacitor grounding network improves stability and accuracy. By using multiple resistor-capacitor combinations in parallel, the stability and accuracy of frequency setting can be improved, the error caused by the tolerance of a single component can be reduced, and the reliability of the system can be improved.

[0059] The parallel resistor R27 and the plurality of resistors and capacitors combined together can effectively reduce the influence of noise and voltage fluctuations in the circuit on the triggering and operating frequency, thereby improving the performance of the backlight controller.

[0060] By adjusting the values ​​of each resistor and capacitor, the required trigger and operating frequency time can be flexibly set to meet different application requirements.

[0061] It can be seen that the RC grounding network design makes the operating frequency and triggering time of the backlight controller U10 more stable and accurate, while improving the anti-interference ability and the reliability of the overall system.

[0062] Terminal 18 of the backlight controller U10 is a trigger and operating frequency time setting capacitor terminal, which is grounded through capacitor C34;

[0063] The 19th terminal of the backlight controller U10 is a third driving signal output terminal;

[0064] The terminal 20 of the backlight controller U10 is a fourth driving signal output terminal.

[0065] See also Figure 5 The four driving ports in the backlight source driving circuit are respectively connected to the first driving signal output terminal, the second driving signal output terminal, the third driving signal output terminal and the first driving signal output terminal of the backlight controller U10, and the output ports V1+, V11, V2+ and V2- of the backlight source driving circuit are connected to the light board.

[0066] The first group of driving circuits of the backlight source driving circuit includes a transformer T2, a PMOS tube Q22 and an NMOS tube Q13. The gates of the PMOS tube Q22 and the NMOS tube Q13 are respectively connected to the first driving signal output terminal and the second driving signal output terminal of the backlight controller U10, the source of the PMOS tube Q22 is connected to the drain of the NMOS tube Q13, the source of the NMOS tube Q13 is grounded, and the drain of the PMOS tube Q22 is connected to the power supply VCC1.

[0067] The first end of the primary coil of the transformer T2 is connected to the drain of the NMOS tube Q13 through the capacitor C61, and the second end of the primary coil of the transformer T2 is grounded; the first end of the secondary coil of the transformer T2 outputs the first positive power supply V1+ to supply power to the light board through the fast recovery diode D20, and the second end of the secondary coil serves as the first negative power supply V1- to supply power to the light board. The anode of the diode D20 is connected to the first end of the secondary coil, and the cathode of the diode D20 is connected to the second end of the secondary coil through the high-frequency low-resistance electrolytic capacitor C63.

[0068] Furthermore, a first RC circuit is connected in parallel at both ends of the diode D20, and the first RC circuit includes a capacitor C62 and a resistor R78 connected in series, a first end of the capacitor C62 is connected to the anode of the diode D20, a second end of the capacitor C62 is connected to the first end of the resistor R78, and a second end of the resistor R78 is connected to the cathode of the diode D20.

[0069] A resistor R79 and a Zener diode Z5 are also connected in series between the first positive power supply electrode V1+ and the first negative power supply electrode V1-. The first end of the resistor R79 is connected to the cathode of the diode D20, the second end of the resistor R79 is connected to the cathode of the Zener diode Z5, and the anode of the Zener diode Z5 is connected to the second end of the secondary coil.

[0070] Furthermore, a diode D19 is connected in reverse series at both ends of the primary coil of the transformer T2, with a common cathode, and the anode of the diode D19 is connected to both ends of the primary coil. In the transformer of the switching power supply, the MOS tube will generate voltage spikes when it is turned on and off. The diode connected in reverse series can absorb these spike voltages and protect the switching element from overvoltage damage. When the switching element is turned off, the current in the primary coil will drop rapidly, generating a high-amplitude reverse voltage. The diode connected in reverse series can limit the amplitude of the reverse voltage and prevent the reverse voltage from damaging the circuit. Voltage spikes and reverse voltages will generate high-frequency noise and increase electromagnetic interference. The buffering effect of the reverse series diode can reduce the amplitude of the high-frequency noise, thereby reducing EMI interference to surrounding circuits and equipment.

[0071] The gate of the PMOS tube Q22 is connected to two diodes D18 connected in series in the forward direction, the anode of the lower diode is grounded, the cathode of the upper diode is connected to the power supply, and the common node of the two diodes is connected to the gate of the MOS tube. When the gate voltage of the MOS tube exceeds the total forward conduction voltage of the two diodes, the diode begins to conduct, limiting the gate voltage from rising. If the gate voltage is lower than the total forward voltage drop of the two diodes, the diode will not conduct, and the gate voltage can change freely. The beneficial effects are to prevent the gate voltage from being too high, protect the MOS tube from damage, ensure that the MOS tube is within a safe operating voltage range, and prevent reliability problems caused by overdriving.

[0072] The second group of driving circuits of the backlight driving circuit includes a transformer T3, a PMOS transistor Q16 and an NMOS transistor Q15, and its principle and function are the same as those of the first group of driving circuits.

[0073] In summary, the utility model provides a backlight driving circuit that isolates power through a transformer to reduce the impact of the front stage on the back stage. A fast recovery diode is used in the circuit for rectification, and the power is output to the load through high-frequency low-resistance electrolytic filtering to improve the response speed. In order to further reduce the reverse spike of the diode, an RC circuit is added to the fast recovery diode for filtering.

[0074] In traditional circuits, energy storage inductors and switching tubes are often used to control the brightness of LEDs. However, this circuit uses high-frequency transformers and drive circuits to achieve electrical isolation between the front and rear stages while taking into account efficient energy conversion, which has better energy-saving effects and can control the brightness more stably.

[0075] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A backlight source driving circuit, comprising a backlight controller U10, characterized in that: A first group of driving circuits and a second group of driving circuits connected to the signal output terminal of the backlight controller U10 are provided; The first driving circuit group includes a high-frequency transformer T2, a PMOS transistor Q22 and an NMOS transistor Q13. The gates of the PMOS transistor Q22 and the NMOS transistor Q13 are respectively connected to the first driving signal output terminal and the second driving signal output terminal of the backlight controller U10. The source of the PMOS transistor Q22 is connected to the drain of the NMOS transistor Q13. The source of the NMOS transistor Q13 is grounded. The drain of the PMOS transistor Q22 is connected to the power supply VCC1. The first end of the primary coil of the transformer T2 is connected to the drain of the NMOS tube Q13 through the capacitor C61, and the second end of the primary coil of the transformer T2 is grounded; the first end of the secondary coil of the transformer T2 outputs the first positive power supply V1+ to supply power to the lamp board through the fast recovery diode D20, and the second end of the secondary coil serves as the first negative power supply V1- to supply power to the lamp board, and the cathode of the diode D20 is connected to the second end of the secondary coil through the high-frequency low-resistance electrolytic capacitor C63.

2. A backlight source driving circuit according to claim 1, characterized in that: A first RC circuit is connected in parallel at both ends of the diode D20. The first RC circuit includes a capacitor C62 and a resistor R78 connected in series. The first end of the capacitor C62 is connected to the anode of the diode D20, the second end of the capacitor C62 is connected to the first end of the resistor R78, and the second end of the resistor R78 is connected to the cathode of the diode D20.

3. A backlight source driving circuit according to claim 2, characterized in that: A resistor R79 and a Zener diode Z5 are also connected in series between the first positive power supply electrode V1+ and the first negative power supply electrode V1-. The first end of the resistor R79 is connected to the cathode of the diode D20, the second end of the resistor R79 is connected to the cathode of the Zener diode Z5, and the anode of the Zener diode Z5 is connected to the second end of the secondary coil.

4. The backlight source driving circuit according to claim 3, characterized in that: A diode D19 connected in reverse series is connected at both ends of the primary coil of the transformer T2, with a common cathode. The anode of the diode D19 is connected to both ends of the primary coil respectively.

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