Timing control circuit for improving ac voltage drop-out of lamp bar direct push converter

Abstract

The utility model discloses the timing control circuit of improvement light bar direct -push converter ac voltage power failure, including first to third MOS pipe, first diode, second diode and supporting resistance and capacitance element. Utilize first diode and first capacitor direct -push converter output's voltage as direct -push converter whether normal work's instruction signal. When direct -push converter normal work, allow the backlight start -stop signal control constant current controller power supply of MCU, when ac voltage drops or fast switch, force synchronous close LED constant current controller's power supply, make it enter reset state. The utility model ensures that constant current controller resets and restarts synchronously when converter restarts, avoids the short circuit (SCP protection) of lamp bar of constant current controller misjudgment caused by timing misplacement, solves LED lamp bar display abnormal problem.

Description

Technical Field

[0001] This utility model relates to the field of display device driving technology, and in particular to a timing control circuit that improves the AC voltage power failure of a direct-drive converter for LED strips. Background Technology

[0002] Currently, large-size LCD monitor backlights primarily use LED strips. To improve efficiency and reduce costs, the LED strip drive circuits generally employ a direct-drive method. A DC / DC converter transforms the voltage from the mains capacitor to the voltage required by the LED strip, and its output directly drives the positive terminal of each strip. Each strip's negative terminal is connected to a constant current control circuit. The error signals from these constant current control circuits serve as negative feedback signals to the DC / DC converter's feedback circuit, adjusting the converter's output voltage and thus stabilizing the output current of each strip. The DC / DC converter can be an LLC converter, a flyback converter, or an asymmetric half-bridge converter, etc. This proposal uses an LLC DC / DC converter as an example. The constant current control circuit modules connected to the negative terminals of each strip can be independent or multiple modules connected in parallel. If they are independent, it is a local dimming backlight system; if they are connected in parallel, it is a single-strip backlight system.

[0003] The LED strip operates over a wide voltage range, especially under DC dimming conditions, where the operating voltage differs significantly between high and low brightness states. Furthermore, different LCD panel models exhibit variations in their LED strip voltages. To improve compatibility while maintaining efficiency and reliability, designs typically maximize the gain range of the LLC converter. Therefore, this LLC DC / DC converter provides power to the LED strip via a single output. The power supply for the LED strip's constant current control circuit and the TL431 pull-up resistor in the LLC converter's feedback loop is provided by a separate standby converter, i.e., 18V. A switching circuit is added between the 18V and the Vcc terminal of the LED strip's constant current control IC to control the backlight's on / off state. As shown in the diagram, the backlight on / off control signal (Backlight_on / off) output from the MCU is divided by R9912 and R9915 to drive Q9813, thereby controlling the switch of Q9814. When the backlight start / stop control signal is high, Q9813 and Q9814 are saturated and turned on, connecting 18V and LED_Vcc to power the constant current control ICs of each LED strip. When the backlight start / stop control signal is low, Q9813 and Q9814 are turned off, and the constant current control IC Vcc of the LED strip is not powered and does not work.

[0004] When the LLC DC / DC converter is off and the LED strip constant current controller is working normally, the constant current controller detects insufficient LED strip current and pulls the ADJF PIN voltage low, i.e., the COMP voltage is pulled low. R9123 and R9135 are connected in parallel, setting the VLED_VS voltage to the highest potential. If AC voltage is suddenly supplied at this time, the LLC DC / DC converter immediately starts working, and its output voltage will be output according to the highest potential set by the constant current controller. After subtracting the voltage drop of the LED strip from this voltage, the remaining part is applied to the constant current controller IC. When this voltage exceeds the SCP protection point voltage of the constant current control IC, the control IC will determine that the LED strip has a short circuit, turn off and latch the string of LED strips, thus causing the LED strip display to malfunction. Figure 2 The waveform shown indicates that when the AC voltage drops, some LED strips activate SCP protection, causing the total current of the LED strips to decrease from 4.125A to 3.175A.

[0005] As can be seen, the LED strip drive system, which consists of three circuit modules—LLC converter, LED strip constant current controller, and Standby converter—can have its switching sequence set by adjusting circuit parameters during normal power-on and power-off. However, under conditions of AC voltage drop or rapid power-on and power-off, the set sequence often becomes misaligned. Abnormal timing often causes the constant current controller to trigger SCP short-circuit protection, resulting in abnormal LED strip lighting. Utility Model Content

[0006] The purpose of this invention is to effectively eliminate the problem of abnormal operation of LED backlight of display under harsh application conditions such as AC voltage drops and various rapid power-on and power-off, and to provide a timing control circuit to improve the AC voltage failure of the LED strip direct drive converter, thereby effectively improving the reliability of the LED strip direct drive system under AC voltage drops and rapid power-on and power-off.

[0007] The technical solution adopted in this utility model is:

[0008] An improved timing control circuit for AC voltage failure in a direct-drive LED strip converter includes a first diode, a second diode, a first MOSFET, a second MOSFET, and a third MOSFET.

[0009] The output of the LED strip's direct-drive converter is connected to the anode of the first diode. The cathode of the first diode is connected to one end of the first capacitor and one end of the first resistor. The other end of the first capacitor is grounded. The other end of the first resistor is connected to one end of the second capacitor, one end of the second resistor, the cathode of the Zener diode, and the gate of the first MOSFET. The other end of the second capacitor, the other end of the second resistor, the anode of the Zener diode, and the source of the first MOSFET are grounded. The drain of the first MOSFET is connected to one end of the third resistor, one end of the fourth resistor, and the gate of the second MOSFET. The other end of the third resistor is connected to the power supply. The other end of the fourth resistor and the source of the second MOSFET are grounded. The drain of the second MOSFET is connected to the gate of the third MOSFET, one end of the third capacitor, one end of the fifth resistor, and one end of the sixth resistor. The other ends of the third capacitor and the sixth resistor are grounded. The other end of the fifth resistor is connected to the backlight on / off control signal output by the microcontroller (MCU).

[0010] The source (S) of the third MOSFET is grounded, and the drain (D) of the third MOSFET is connected to one end of the seventh resistor. The power supply is connected to one end of the eighth resistor, the emitter of the transistor, and the cathode of the second diode. The other end of the seventh resistor is connected to the other end of the eighth resistor and the base of the transistor. The collector of the transistor is connected to the anode of the second diode, one end of the fourth capacitor, and the Vcc power supply terminal of the LED strip constant current control IC. The other end of the fourth capacitor is grounded.

[0011] Furthermore, the first diode is a fast recovery diode; alternatively, the first diode is a UF4007 diode.

[0012] Furthermore, the second diode is a fast-switching diode; as an optional implementation, the second diode is a 1N4148 diode.

[0013] Furthermore, the first and second capacitors are both 10NF capacitors; the third capacitor is 100NF; and the fourth capacitor is a 2.2μF 25V capacitor.

[0014] Furthermore, the first MOSFET, the second MOSFET, and the third MOSFET are all MOSFETs of model number 2N7002K.

[0015] Furthermore, the resistance of the first resistor is 82kΩ; the resistance of the second resistor is 13kΩ; the resistance of the third and fourth resistors is 10kΩ; the resistance of the fifth resistor is 1kΩ; the resistance of the sixth resistor is 510kΩ; the resistance of the seventh resistor is 8.8kΩ with an accuracy of 1%; and the resistance of the eighth resistor is 1kΩ.

[0016] Furthermore, the power supply is provided by a standby converter.

[0017] Furthermore, the power supply is 18V.

[0018] Furthermore, the direct-drive converter is an LLC DC / DC converter, a Flyback converter, or an asymmetric half-bridge converter.

[0019] This invention employs the above technical solution, utilizing the voltage output of the direct-drive converter via the first diode and first capacitor as an indicator signal to determine whether the direct-drive converter is operating normally. When the direct-drive converter is operating normally, the MCU's backlight on / off signal (Backlight_on / off) controls the constant current controller's power supply. When the AC voltage drops or the power is switched on / off rapidly, the power supply (Vcc) to the LED constant current controller is forcibly and synchronously shut off, causing it to enter a reset state. This invention ensures that when the converter restarts, the constant current controller resets and restarts synchronously, avoiding misjudgment of a short circuit in the LED strip due to timing misalignment (SCP protection), thus resolving the problem of abnormal LED strip display. Attached Figure Description

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments;

[0021] Figure 1 This is a schematic diagram of the timing control circuit for improving the AC voltage power failure of the direct-drive converter for LED strips, as described in this utility model.

[0022] Figure 2 This is a schematic diagram of the test waveforms of the driving circuit in the prior art;

[0023] Figure 3 This is an overall schematic diagram of the LED strip drive circuit using the timing control circuit of this utility model;

[0024] Figure 4 This is a schematic diagram of the test waveform of the timing control circuit for improving the AC voltage failure of the direct-drive converter for light strips, which is a feature of this invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings.

[0026] like Figure 1 As shown in Figure 3 or 4, this utility model discloses a timing control circuit for improving the AC voltage power failure of a direct-drive LED strip converter, which includes a first diode, a second diode, a first MOSFET, a second MOSFET, and a third MOSFET.

[0027] The output of the LED strip's direct-drive converter is connected to the anode of the first diode. The cathode of the first diode is connected to one end of the first capacitor and one end of the first resistor. The other end of the first capacitor is grounded. The other end of the first resistor is connected to one end of the second capacitor, one end of the second resistor, the cathode of the Zener diode, and the gate of the first MOSFET. The other end of the second capacitor, the other end of the second resistor, the anode of the Zener diode, and the source of the first MOSFET are grounded. The drain of the first MOSFET is connected to one end of the third resistor, one end of the fourth resistor, and the gate of the second MOSFET. The other end of the third resistor is connected to the power supply. The other end of the fourth resistor and the source of the second MOSFET are grounded. The drain of the second MOSFET is connected to the gate of the third MOSFET, one end of the third capacitor, one end of the fifth resistor, and one end of the sixth resistor. The other ends of the third capacitor and the sixth resistor are grounded. The other end of the fifth resistor is connected to the backlight on / off control signal output by the microcontroller (MCU).

[0028] The source (S) of the third MOSFET is grounded, and the drain (D) of the third MOSFET is connected to one end of the seventh resistor. The power supply is connected to one end of the eighth resistor, the emitter of the transistor, and the cathode of the second diode. The other end of the seventh resistor is connected to the other end of the eighth resistor and the base of the transistor. The collector of the transistor is connected to the anode of the second diode, one end of the fourth capacitor, and the Vcc power supply terminal of the LED strip constant current control IC. The other end of the fourth capacitor is grounded.

[0029] Furthermore, the first diode is a fast recovery diode; alternatively, the first diode is a UF4007 diode.

[0030] Furthermore, the second diode is a fast-switching diode; as an optional implementation, the second diode is a 1N4148 diode.

[0031] Furthermore, the first and second capacitors are both 10NF capacitors; the third capacitor is 100NF; and the fourth capacitor is a 2.2μF 25V capacitor.

[0032] Furthermore, the first MOSFET, the second MOSFET, and the third MOSFET are all MOSFETs of model number 2N7002K.

[0033] Furthermore, the resistance of the first resistor is 82kΩ; the resistance of the second resistor is 13kΩ; the resistance of the third and fourth resistors is 10kΩ; the resistance of the fifth resistor is 1kΩ; the resistance of the sixth resistor is 510kΩ; the resistance of the seventh resistor is 8.8kΩ with an accuracy of 1%; and the resistance of the eighth resistor is 1kΩ.

[0034] Furthermore, the power supply is provided by a standby converter.

[0035] Furthermore, the power supply is 18V.

[0036] Furthermore, the direct-drive converter can be an LLC DC / DC converter, a Flyback converter, or an asymmetric half-bridge converter. It supports various direct-drive converter topologies (LLC, Flyback, asymmetric half-bridge, etc.) to adapt to the LED strip voltage requirements of different LCD panels.

[0037] This invention detects the output status of the direct-drive converter using a first diode. When the AC power fails or the converter shuts down due to rapid switching, a combination of MOSFETs forcibly cuts off the Vcc power supply to the LED constant current control IC, causing it to reset synchronously. When the converter restarts, the constant current controller resets synchronously and resumes operation. This invention completely eliminates the problem of false short-circuit protection (SCP) of the constant current controller caused by timing mismatch, and solves the problem of abnormal LED light bar display under AC voltage drop or rapid switching conditions. The anti-interference capability is improved through RC filtering (such as C9911, R9907) and Zener diode (ZD9407), ensuring reliability under harsh conditions. This circuit is compatible with various converter topologies such as LLC and Flyback, and is low in cost and easy to integrate.

[0038] The specific principles of this utility model will be explained in detail below:

[0039] like Figure 1As shown, the circuit connection of this utility model is as follows: The positive terminal of the first diode D9902 is connected to PIN9 of the direct-drive converter (LLC transformer) T9101 of the light strip; the negative terminal of D9902 is connected to one end of the first capacitor C9910 and one end of the first resistor R9906; the other end of the first capacitor C9910 is grounded; the other end of the first resistor R9906 is connected to one end of the second capacitor C9911, one end of the second resistor R9907, the negative terminal of the Zener diode ZD9407, and the gate (G) of the first MOSFET Q9810; the other end of the second capacitor C9911, the other end of the second resistor R9907, the positive terminal of the Zener diode ZD9407, and the source (S) of the first MOSFET Q9810 are all grounded. The drain of the first MOSFET Q9810 is connected to one end of the third resistor R9909, one end of the fourth resistor R9910, and the gate of the second MOSFET Q9811. The other end of the third resistor R9909 is connected to the power supply (18V), the other end of the fourth resistor R9910 is grounded, and the source of the second MOSFET Q9811 is grounded. The drain of the second MOSFET Q9811 is connected to the gate of the third MOSFET Q9813, one end of the third capacitor C9912, one end of the sixth resistor R9915, and one end of the fifth resistor R9912. The other end of the third capacitor C9912 is grounded, the other end of the sixth resistor R9915 is grounded, and the other end of the fifth resistor R9912 is connected to the Backlight_on / off control signal.

[0040] The source (S) of the third MOSFET Q9813 is grounded, and the drain (D) of the third MOSFET Q9813 is connected to one end of the seventh resistor R9913. The power supply is connected to one end of the eighth resistor R9911, the emitter of the transistor Q9814Q, and the cathode of the second diode D9903. The other end of the seventh resistor R9913 is connected to the other end of the eighth resistor R9911 and the base of the transistor Q9814. The collector of the transistor Q9814 is connected to the anode of the second diode D9903, one end of the fourth capacitor C9913, and the Vcc power supply terminal of the LED strip constant current control IC. The other end of the fourth capacitor C9913 is grounded.

[0041] Working principle introduction:

[0042] This invention utilizes the voltage generated by the rectification and filtering of the secondary winding of LLC transformer T9101 from D9902 and C9910 as an indication signal for whether the LLC DC / DC converter is working properly.

[0043] When the LLC DC / DC converter is working normally, the PWM signal output from PIN9 of the LLC transformer T9101, after being rectified and filtered by D9902 and C9910, becomes a DC signal that is then divided by R9906 and R9907 and smoothed by C9911 to eliminate interference. This signal then drives the gate (G) of Q9810. The drain (D) of Q9810 is pulled up by R9909 and supplied with 18V by the standby circuit, ensuring Q9810 is fully saturated and conducting. The main function of ZD9407 is to clamp the voltage to prevent it from exceeding the gate-side voltage (GS) of Q9810 and damaging it. The drain voltage of Q9810 is lower than the gate threshold voltage of Q9811, thus Q9811 is cut off. Therefore, the Vcc power supply of the LED strip constant current control IC is controlled by the Backlight_on / off signal output by the MCU, and the LED strip drive system works normally.

[0044] When the LLC DC / DC converter is in the off state due to an AC voltage drop or rapid power-on / off, there is no output voltage at pin 9 of the LLC transformer T9101, and the output voltage of the D9902 and C9910 rectifier and filter circuits is zero. Therefore, Q9810 is cut off. If the 18V supplied by the Standby circuit module is present at this time, the 18V voltage, after being divided by R9909 and R9910, drives Q9811 to saturation conduction, pulling the gate potential of Q9813 low, causing Q9813 to cut off. Consequently, Q9814 is also cut off. At this point, regardless of whether the Backlight_on / off signal output by the MCU is high or low, it is impossible to control the output of 18V voltage to LED_Vcc to power the constant current control ICs, thus ensuring that the LED strip constant current controller is also off when the LLC DC / DC converter is in the off state. Therefore, once the LLC DC / DC converter enters the off state, it will simultaneously turn off the Vcc of the LED strip constant current control IC, and the LED strip constant current controller will enter the Reset state.

[0045] The next time the LLC DC / DC converter starts working, the LED strip constant current controller will start simultaneously. This ensures that the LED strip constant current controller can reset and restart every time the LLC DC / DC converter starts working, thus eliminating SCP protection problems caused by timing mismatch between the LLC DC / DC converter and the LED strip constant current controller due to AC voltage drops or rapid switching. Figure 4 As shown in the test waveform after adding the countermeasure circuit, it can be seen that during the AC voltage drop transient process, the positive terminal voltage of the LED light strip did not overshoot, and the LED light strip current returned to normal after recovery.

[0046] This invention employs an RC filter (such as C9911, R9907) and a Zener diode (ZD9407) design to filter out interference noise from the LLC output signal and prevent false triggering of the MOSFET. It also clamps the MOSFET gate voltage (such as the G terminal of Q9810) to prevent overvoltage damage to components and ensures stable circuit operation under harsh conditions such as voltage fluctuations and rapid power-on / off.

[0047] This invention employs the above technical solution, utilizing the voltage output of the direct-drive converter via the first diode and first capacitor as an indicator signal to determine whether the direct-drive converter is operating normally. When the direct-drive converter is operating normally, the MCU's backlight on / off signal (Backlight_on / off) controls the constant current controller's power supply. When the AC voltage drops or the power is switched on / off rapidly, the power supply (Vcc) to the LED constant current controller is forcibly and synchronously shut off, causing it to enter a reset state. This invention ensures that when the converter restarts, the constant current controller resets and restarts synchronously, avoiding misjudgment of a short circuit in the LED strip due to timing misalignment (SCP protection), thus resolving the problem of abnormal LED strip display.

[0048] Obviously, the described embodiments are only a part of the embodiments of this application, not all of them. Without conflict, the embodiments and features in the embodiments of this application can be combined with each other. The components of the embodiments of this application described and illustrated herein can generally be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. An improved timing control circuit for LED strip direct-drive converters to address AC voltage failure during power loss, characterized by: It includes a first diode, a second diode, a first MOSFET, a second MOSFET, and a third MOSFET; The output of the LED strip's direct-drive converter is connected to the anode of the first diode. The cathode of the first diode is connected to one end of the first capacitor and one end of the first resistor. The other end of the first capacitor is grounded. The other end of the first resistor is connected to one end of the second capacitor, one end of the second resistor, the cathode of the Zener diode, and the gate (G) of the first MOSFET. The other end of the second capacitor, the other end of the second resistor, the anode of the Zener diode, and the source (S) of the first MOSFET are grounded. The drain (D) of the first MOSFET is connected to one end of the third resistor, one end of the fourth resistor, and the gate (G) of the second MOSFET. The other end of the third resistor is connected to the power supply. The other end of the fourth resistor and the source (S) of the second MOSFET are grounded. The drain of the second MOSFET is connected to the gate (G) of the third MOSFET, one end of the third capacitor, one end of the fifth resistor, and one end of the sixth resistor. The other ends of the third capacitor and the sixth resistor are grounded. The other end of the fifth resistor is connected to the backlight start / stop control signal output by the microcontroller (MCU). The source (S) of the third MOSFET is grounded, and the drain (D) of the third MOSFET is connected to one end of the seventh resistor. The power supply is connected to one end of the eighth resistor, the emitter of the transistor, and the cathode of the second diode. The other end of the seventh resistor is connected to the other end of the eighth resistor and the base of the transistor. The collector of the transistor is connected to the anode of the second diode, one end of the fourth capacitor, and the Vcc power supply terminal of the LED strip constant current control IC. The other end of the fourth capacitor is grounded.

2. The timing control circuit for improving the AC voltage failure of the direct-drive converter for LED strips according to claim 1, characterized in that: The first diode is a fast recovery diode.

3. The timing control circuit for improving the AC voltage failure of the direct-drive converter for LED strips according to claim 1, characterized in that: The second diode is a fast-switching diode.

4. The timing control circuit for improving AC voltage power failure in direct-drive LED strip converters according to claim 1, characterized in that: The first and second capacitors are both 10NF capacitors; the third capacitor is 100NF; and the fourth capacitor is a 2.2μF 25V capacitor.

5. The timing control circuit for improving the AC voltage failure of the direct-drive converter for LED strips according to claim 1, characterized in that: The first, second, and third MOSFETs are all MOSFETs of model 2N7002K.

6. The timing control circuit for improving AC voltage power failure in direct-drive LED strip converters according to claim 1, characterized in that: The first resistor has a resistance of 82kΩ; the second resistor has a resistance of 13kΩ; the third and fourth resistors both have a resistance of 10kΩ; the fifth resistor has a resistance of 1kΩ; the sixth resistor has a resistance of 510kΩ; the seventh resistor has a resistance of 8.8kΩ with an accuracy of 1%; and the eighth resistor has a resistance of 1kΩ.

7. The timing control circuit for improving the AC voltage failure of the direct-drive converter for LED strips according to claim 1, characterized in that: The power supply is provided by a standby converter.

8. The timing control circuit for improving the AC voltage failure of the direct-drive converter for LED strips according to claim 1, characterized in that: The power supply is 18V.

9. The timing control circuit for improving AC voltage failure in direct-drive LED strip converters according to claim 1, characterized in that: The direct-drive converter can be an LLC DC / DC converter, a Flyback converter, or an asymmetric half-bridge converter.

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