Time sequence control circuit for improving poor alternating voltage power failure of light bar direct-push converter

Abstract

The invention discloses a time sequence control circuit for improving poor AC voltage power failure of a light bar direct-push converter. The time sequence control circuit comprises a first MOS transistor, a second MOS transistor, a third MOS transistor, a first diode, a second diode and a matched resistor-capacitor element. The voltage output by the first diode and the first capacitor direct-push converter is used as an indication signal for indicating whether the direct-push converter works normally or not. When the direct push converter works normally, a backlight start-stop signal of the MCU is allowed to control the constant current controller to supply power; and when the alternating voltage drops or is quickly turned on and off, the power supply of the LED constant-current controller is forcibly and synchronously turned off, so that the LED constant-current controller enters a reset state. According to the invention, when the converter is restarted, the constant current controller is synchronously reset and restarted, so that misjudgment of light bar short circuit (SCP protection) of the constant current controller due to time sequence dislocation is avoided, and the problem of abnormal display of the LED light bar is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of display device driving, and in particular to a timing control circuit for improving the AC voltage power-off problem of a light bar direct-drive converter. Background Art

[0002] Currently, large-size LCD monitor backlights primarily utilize LED light strips. To improve efficiency and reduce costs, the driver circuit for LED light strips typically employs a direct-drive approach. A DC / DC converter converts the voltage on a power-frequency capacitor to the voltage required by the LED light strips. Its output directly drives the positive terminal of each light strip, while the negative terminal of each light strip is connected to a constant-current control circuit. The error signal from these constant-current control circuits is fed as negative feedback to the DC / DC converter's feedback circuit, regulating the DC / DC converter's output voltage and thus stabilizing the output current of each light strip. The DC / DC converter can be an LLC converter, a flyback converter, or an asymmetric half-bridge converter. This proposal uses an LLC DC / DC converter as an example. The constant-current control circuit module connected to the negative terminal of each light strip can be independent or multiple modules connected in parallel. If independent, this constitutes a local dimming backlight system. If connected in parallel, this constitutes a single-light strip backlight system.

[0003] LED light strips have a wide operating voltage range, especially when using DC dimming. The operating voltage varies significantly between high and low brightness settings. Furthermore, different LCD panel models have varying operating voltages. To improve compatibility, while maintaining efficiency and reliability, designs typically maximize the LLC converter's gain range. Therefore, this LLC DC / DC converter uses a single output to power the LED light strip. A separate standby converter provides 18V power for the LED light strip's constant current control circuit and the TL431 pull-up resistor in the LLC converter's feedback loop. A switch circuit is added between the 18V supply and the Vcc terminal of the LED light strip's constant current control IC to control the backlight on and off. As shown in the figure, the backlight on / off control signal (Backlight_on / off) output by the MCU is divided by R9912 and R9915, driving Q9813, which in turn controls Q9814 on and off. When the backlight start-stop control signal is high, Q9813 is saturated and turned on, Q9814 is also saturated and turned on, 18V and LED_Vcc are connected, and power is supplied to the constant current control IC of each LED light strip; when the backlight start-stop control signal is low, Q9813 is cut off, Q9814 is also cut off, and the LED light strip constant current control IC Vcc has no power and does not work.

[0004] When the LLC DC / DC converter is in the off state and the LED light bar constant current controller is working normally, the constant current controller detects that the LED light bar current is insufficient and pulls down the ADJF PIN voltage, that is, the COMP voltage is pulled down, R9123 and R9135 are connected in parallel, and the VLED_VS voltage is set to the highest potential. At this time, if the AC voltage is suddenly supplied, the LLC DC / DC converter will be in working state immediately, and its output voltage will be output according to the highest potential set by the constant current controller. After deducting the voltage drop of the LED light bar from this voltage, the remaining part is added 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 light bar has a short circuit, turn off this string of LED light bars and latch it, so that the LED light bar displays abnormally. Figure 2 The waveform shown shows that when the AC voltage drops, some light strips trigger SCP protection, so the total current of the LED light strip drops from the original 4.125A to 3.175A.

[0005] It can be seen that the LED light strip drive system, which consists of three circuit modules: LLC converter, LED light strip constant current controller and Standby converter, can set the power on and off timing of each module circuit by adjusting the circuit parameters during normal power on and off. However, in the case of AC voltage drop or rapid power on and off, the above set timing will often be misaligned and abnormal. Abnormal timing will often cause the constant current controller to trigger the SCP short-circuit protection, resulting in abnormal lighting of the LED light strip. Summary of the Invention

[0006] The purpose of the present invention is to effectively prevent abnormal operation of the display LED backlight under harsh application conditions such as AC voltage drops and various rapid power on and off, and to provide a timing control circuit to improve the poor AC voltage power off of the light bar direct drive converter, thereby effectively improving the reliability of the LED light bar direct drive system during AC voltage drops and rapid power on and off.

[0007] The technical solution adopted in the present invention is: A timing control circuit for improving the AC voltage power failure of a light bar direct-drive converter, comprising a first diode, a second diode, a first MOS transistor, a second MOS transistor, and a third MOS transistor; The output end of the direct-drive converter of the light bar 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 voltage-stabilizing diode and the G pole of the first MOS tube, the other end of the second capacitor, the other end of the second resistor, the anode of the voltage-stabilizing diode and the S pole of the first MOS tube are grounded; the D pole of the first MOS tube is connected to one end of the third resistor, one end of the fourth resistor and the G pole of the second MOS tube; the other end of the third resistor is connected to the power supply, the other end of the fourth resistor and the S pole of the second MOS tube are grounded; the D pole of the second MOS tube is connected to the G pole of the third MOS tube, one end of the third capacitor, one end of the fifth resistor and one end of the sixth resistor; the other end of the third capacitor and the other end of the sixth resistor are grounded, and the other end of the fifth resistor is connected to the backlight start / stop control signal (Backlight_on / off) output by the microcontroller MCU; The S pole of the third MOS tube is grounded, the D pole of the third MOS tube is connected to one end of the seventh resistor, the power supply is respectively 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 respectively connected to the other end of the eighth resistor and the base of the transistor, the collector of the transistor is respectively connected to the anode of the second diode, one end of the fourth capacitor and the Vcc power supply end of the LED light bar constant current control IC, and the other end of the fourth capacitor is grounded.

[0008] Furthermore, the first diode is a fast recovery diode. As an optional implementation, the first diode is a UF4007 diode.

[0009] Furthermore, the second diode is a fast switching diode. As an optional implementation, the second diode is a 1N4148 diode.

[0010] Furthermore, the first capacitor and the second capacitor are both 10NF capacitors; the third capacitor is 100NF; and the fourth capacitor is 2.2μF 25V capacitor.

[0011] Furthermore, the first MOS tube, the second MOS tube and the third MOS tube are all 2N7002K MOS tubes.

[0012] Furthermore, the resistance of the first resistor is 82kΩ; the resistance of the second resistor is 13kΩ; the resistance of the third resistor and the fourth resistor are both 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 and the accuracy is 1%; and the resistance of the eighth resistor is 1kΩ.

[0013] Furthermore, the power supply is provided by a Standby converter.

[0014] Furthermore, the power supply is 18V.

[0015] Furthermore, the direct-drive converter is an LLC DC / DC converter, a Flyback converter or an asymmetric half-bridge converter.

[0016] The present invention adopts the above technical solution, utilizing the voltage output by the direct-drive converter, which uses the first diode and the first capacitor, as an indicator of whether the direct-drive converter is operating properly. When the direct-drive converter is operating normally, the MCU's backlight on / off signal (Backlight_on / off) is allowed to control the constant current controller's power supply. When the AC voltage drops or the device is rapidly powered on and off, the power supply (Vcc) to the LED constant current controller is forcibly shut off, forcing it into a reset state. This invention ensures that when the converter is restarted, the constant current controller is synchronously reset and restarted, preventing the constant current controller from misjudging the light bar as a short circuit (SCP protection) due to timing misalignment, thereby resolving the issue of abnormal LED light bar display. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments; Figure 1 This is a schematic diagram of the structure of the timing control circuit for improving the AC voltage power failure of the light bar direct-drive converter according to the present invention; Figure 2 Schematic diagram of test waveform of driving circuit in the prior art; Figure 3 This is an overall schematic diagram of a light bar driving circuit using the timing control circuit of the present invention; Figure 4 This is a test waveform diagram of the timing control circuit for improving the AC voltage power-off problem of the direct-drive converter of the light bar according to the present invention. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application.

[0019] like Figure 1 As shown in 3 or 4, the present invention discloses a timing control circuit for improving the AC voltage power-off problem of a light bar direct-drive converter, which includes a first diode, a second diode, a first MOS transistor, a second MOS transistor, and a third MOS transistor; The output end of the direct-drive converter of the light bar 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 voltage-stabilizing diode and the G pole of the first MOS tube, the other end of the second capacitor, the other end of the second resistor, the anode of the voltage-stabilizing diode and the S pole of the first MOS tube are grounded; the D pole of the first MOS tube is connected to one end of the third resistor, one end of the fourth resistor and the G pole of the second MOS tube; the other end of the third resistor is connected to the power supply, the other end of the fourth resistor and the S pole of the second MOS tube are grounded; the D pole of the second MOS tube is connected to the G pole of the third MOS tube, one end of the third capacitor, one end of the fifth resistor and one end of the sixth resistor; the other end of the third capacitor and the other end of the sixth resistor are grounded, and the other end of the fifth resistor is connected to the backlight start / stop control signal (Backlight_on / off) output by the microcontroller MCU; The S pole of the third MOS tube is grounded, the D pole of the third MOS tube is connected to one end of the seventh resistor, the power supply is respectively 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 respectively connected to the other end of the eighth resistor and the base of the transistor, the collector of the transistor is respectively connected to the anode of the second diode, one end of the fourth capacitor and the Vcc power supply end of the LED light bar constant current control IC, and the other end of the fourth capacitor is grounded.

[0020] Furthermore, the first diode is a fast recovery diode. As an optional implementation, the first diode is a UF4007 diode.

[0021] Furthermore, the second diode is a fast switching diode. As an optional implementation, the second diode is a 1N4148 diode.

[0022] Furthermore, the first capacitor and the second capacitor are both 10NF capacitors; the third capacitor is 100NF; and the fourth capacitor is 2.2μF 25V capacitor.

[0023] Furthermore, the first MOS tube, the second MOS tube and the third MOS tube are all 2N7002K MOS tubes.

[0024] Furthermore, the resistance of the first resistor is 82kΩ; the resistance of the second resistor is 13kΩ; the resistance of the third resistor and the fourth resistor are both 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 and the accuracy is 1%; and the resistance of the eighth resistor is 1kΩ.

[0025] Furthermore, the power supply is provided by a Standby converter.

[0026] Furthermore, the power supply is 18V.

[0027] Furthermore, the direct-drive converter is an LLC DC / DC converter, a flyback converter, or an asymmetric half-bridge converter. Multiple direct-drive converter topologies (LLC, flyback, asymmetric half-bridge, etc.) are supported to meet the light bar voltage requirements of different LCD panels.

[0028] This invention uses a first diode to detect the output status of the direct-drive converter. When the converter shuts down due to AC power loss or rapid power-on / off, a MOS transistor combination forcibly disconnects the Vcc power supply to the LED constant-current control IC, causing it to reset synchronously. When the converter restarts, the constant-current controller is synchronously reset and resumes operation. This invention completely eliminates the problem of false short-circuit protection (SCP) of the constant-current controller caused by timing mismatch, resolving abnormal LED light bar display during AC voltage drops or rapid power-on / off conditions. RC filtering (such as C9911 and R9907) and a voltage regulator diode (ZD9407) enhance anti-interference capabilities and ensure reliability under harsh conditions. This circuit is compatible with multiple converter topologies, including LLC and flyback, and is low-cost and easy to integrate.

[0029] The specific principle of the present invention is described in detail below: like Figure 1 As shown, the connection relationship of the circuit of the present invention is as follows: Circuit connection relationship: the positive end of the first diode D9902 is connected to PIN9 of the direct-drive converter (LLC transformer) T9101 of the light bar, the negative end of D9902 is connected to one end of the first capacitor C9910 and one end of the first resistor R9906, and 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 end of the Zener diode ZD9407, and the G terminal of the first MOS transistor Q9810; the other end of the second capacitor C9911, the other end of the second resistor R9907, the positive end of the Zener diode ZD9407, and the S terminal of the first MOS transistor Q9810 are all grounded; The D electrode of the first MOS transistor Q9810 is connected to one end of the third resistor R9909, one end of the fourth resistor R9910, and the G electrode of the second MOS transistor 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 S electrode of the second MOS transistor Q9811 is grounded; the D electrode of the second MOS transistor Q9811 is connected to the G electrode of the third MOS transistor 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.

[0030] The S pole of the third MOS transistor Q9813 is grounded, the D pole of the third MOS transistor Q9813 is connected to one end of the seventh resistor R9913, the power supply is respectively 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 respectively connected to the other end of the eighth resistor R9911 and the base of the transistor Q9814, the collector of the transistor Q9814 is respectively 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 light bar constant current control IC, and the other end of the fourth capacitor C9913 is grounded.

[0031] Working principle introduction: The present invention utilizes D9902 and C9910 to generate a voltage from rectification and filtering of the secondary winding of the LLC transformer T9101 as an indication signal of whether the LLC DC / DC converter is operating normally.

[0032] When the LLC DC / DC converter is operating normally, the PWM signal output from PIN 9 of LLC transformer T9101 is rectified and filtered by D9902 and C9910. The resulting DC signal is then divided by R9906 and R9907, and smoothed by C9911 to eliminate interference. It then drives the G terminal of Q9810. The D terminal of Q9810 is pulled up by R9909 and then powered by the 18V provided by the standby circuit, fully saturating and conducting. The ZD9407 acts as a voltage clamp to prevent the voltage from exceeding Q9810's G withstand voltage and damaging it. The D terminal voltage of Q9810 is lower than the G terminal threshold voltage of Q9811, causing Q9811 to turn off. Therefore, the Vcc 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 operates normally.

[0033] 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. The output voltage of the D9902 and C9910 rectifier and filter circuits is zero, so Q9810 is turned off. However, if the 18V voltage provided by the standby circuit module is present at this time, the 18V voltage, after being divided by R9909 and R9910, drives Q9811 into saturation conduction, pulling down the G-pole potential of Q9813, turning off Q9813 and, consequently, Q9814. At this point, regardless of whether the Backlight_on / off signal output by the MCU is high or low, it cannot control the output of 18V voltage to LED_Vcc to power the various constant current control ICs. This ensures that when the LLC DC / DC converter is in the off state, the LED light bar constant current controller is also in the off state. Therefore, once the LLC DC / DC converter enters the off state, the Vcc of the LED light bar constant current control IC will be turned off at the same time, and the LED light bar constant current controller will enter the reset state.

[0034] The next time the LLC DC / DC converter starts working again, the LED light bar constant current controller will start working at the same time, which ensures that the LED light bar constant current controller can be reset and restarted every time the LLC DC / DC converter starts working, thereby eliminating the SCP protection problem caused by the timing mismatch between the LLC DC / DC converter and the LED light bar constant current controller caused by AC voltage drop or rapid power on / off. Figure 4 As shown in the figure, the test waveform after adding the countermeasure circuit shows that during the transient process of AC voltage drop, the positive terminal voltage of the LED light strip does not overshoot, and the current of the LED light strip returns to normal after recovery.

[0035] This invention utilizes an RC filter (e.g., C9911, R9907) and a voltage regulator (ZD9407) to filter out noise interference from the LLC output signal, preventing false triggering of the MOS transistor. It also clamps the MOS transistor gate voltage (e.g., the G terminal of the Q9810) to prevent overvoltage damage to the component, ensuring stable circuit operation under harsh operating conditions such as voltage fluctuations and rapid power on / off.

[0036] The present invention adopts the above technical solution, utilizing the voltage output by the direct-drive converter, which uses the first diode and the first capacitor, as an indicator of whether the direct-drive converter is operating properly. When the direct-drive converter is operating normally, the MCU's backlight on / off signal (Backlight_on / off) is allowed to control the constant current controller's power supply. When the AC voltage drops or the device is rapidly powered on and off, the power supply (Vcc) to the LED constant current controller is forcibly shut off, forcing it into a reset state. This invention ensures that when the converter is restarted, the constant current controller is synchronously reset and restarted, preventing the constant current controller from misjudging the light bar as a short circuit (SCP protection) due to timing misalignment, thereby resolving the issue of abnormal LED light bar display.

[0037] Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. In the absence of conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The components of the embodiments of the present application generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the present application is not intended to limit the scope of the application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

Claims

1. Improve the timing control circuit of the direct-drive converter of the light bar to prevent AC voltage power failure, which is characterized by: It includes a first diode, a second diode, a first MOS transistor, a second MOS transistor and a third MOS transistor; The output end of the direct-drive converter of the light bar 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 voltage-stabilizing diode and the G pole of the first MOS tube, the other end of the second capacitor, the other end of the second resistor, the anode of the voltage-stabilizing diode and the S pole of the first MOS tube are grounded; the D pole of the first MOS tube is connected to one end of the third resistor, one end of the fourth resistor and the G pole of the second MOS tube; the other end of the third resistor is connected to the power supply, the other end of the fourth resistor and the S pole of the second MOS tube are grounded; the D pole of the second MOS tube is connected to the G pole of the third MOS tube, one end of the third capacitor, one end of the fifth resistor and one end of the sixth resistor; the other end of the third capacitor and the other end of the sixth resistor are grounded, and the other end of the fifth resistor is connected to the backlight start and stop control signal output by the microcontroller MCU; The S pole of the third MOS tube is grounded, the D pole of the third MOS tube is connected to one end of the seventh resistor, the power supply is respectively 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 respectively connected to the other end of the eighth resistor and the base of the transistor, the collector of the transistor is respectively connected to the anode of the second diode, one end of the fourth capacitor and the Vcc power supply end of the LED light bar constant current control IC, and the other end of the fourth capacitor is grounded.

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

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

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

5. The timing control circuit for improving AC voltage failure of a light bar direct drive converter according to claim 1, characterized in that: The first MOS tube, the second MOS tube and the third MOS tube are all 2N7002K MOS tubes.

6. The timing control circuit for improving AC voltage failure of a light bar direct drive converter according to claim 1, characterized in that: The resistance of the first resistor is 82kΩ; the resistance of the second resistor is 13kΩ; the resistance of the third resistor and the fourth resistor are both 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.

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

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

9. The timing control circuit for improving AC voltage failure of a light bar direct drive converter according to claim 1, characterized in that: The direct-drive converter is an LLC DC / DC converter, a flyback converter or an asymmetric half-bridge converter.

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