A non-flickering, ultra-quiet, high-power LED lamp switching power supply circuit and soft-start method thereof

Abstract

The present invention discloses a non-flickering ultra-quiet high-power LED lamp switch power supply circuit, which adopts PWM to DC direct current dimming signal to simulate direct current dimming, solves the problem of interference between bright and dark horizontal stripes, achieves a truly non-flickering screen display effect, and solves the problem that the 100HZ-400HZ frequency causes the boost inductor magnetic component to produce abnormal sound. The present invention adopts the transformer Tr11 output voltage, which is rectified by diodes D1 / D2 and filtered by capacitor C6, and then the voltage is directly used to drive the LED lamp, eliminating the traditional Converter Boost boost LED lamp drive circuit, reducing the PD high-power power board BOM material cost price, and at the same time, the LED lamp conversion efficiency can be designed to be at least 98%, which improves the power conversion efficiency of the LED lamp drive circuit in the product power supply, making the product more energy-saving and power-saving.

Description

Technical Field

[0001] The present invention relates to the technical field of switching power supplies for display products, and in particular to a switching power supply circuit of a high-power LED lamp tube which is non-flickering and ultra-quiet and a soft starting method thereof. Background Art

[0002] like Figure 1 As shown, the traditional high-power power board inside the 65-inch PD liquid crystal display product usually uses the main power circuit 2 to output Vout3 voltage such as: 24V / 9A specification to the Converter Boost circuit for voltage conversion, and then generates 50V / 4A specification such as: voltage 50V current 4A to drive the LED lamp when the PWM dimming duty cycle Duty=100%. Since the Converter Boost circuit has better power conversion efficiency in terms of conversion energy efficiency when the LED lamp is low-brightness, the low-frequency PWM dimming adopted by the Converter Boost circuit has better power conversion efficiency than the DC direct current dimming. Therefore, when designing the chip, the LED lamp driver chip manufacturer usually only designs the dimming DIM pin function to receive low-frequency PWM signals, dimming signals (abbreviated as: PWMDIM), such as: 100HZ~400HZ PWM dimming signals, and the use of low-frequency PWM dimming signals in actual circuit design applications often has the following problems that are difficult to solve:

[0003] 1. When the screen driver circuit board (T-CON Source) inside the LCD panel (Panel) is replaced with other manufacturers' parts, the problem of matching between the LCD panel and the screen driver circuit board is often easy to cause the problem of light and dark horizontal stripes interference on the screen, which is difficult to solve.

[0004] 2. When using PWM dimming signals of around 100HZ~400HZ, the frequency is within the audio range received by the human ear. During PWM dimming, the boost inductor magnetic components inside the Converter Boost circuit are prone to produce abnormal sounds, which is difficult to solve.

[0005] 3. Although the human eye cannot perceive the flicker of the LCD screen when using low-frequency PWM dimming, the screen flickering will be noticed when shooting with a mobile phone or camera, and it is impossible to achieve a truly flicker-free screen display effect.

[0006] 4. The traditional Converter Boost circuit is used to drive the LED lamp. The conversion efficiency of this driving circuit is generally around 88%~93%. Taking the 86-inch AOC 86X2 public display PD model produced by TPV as an example, when the Converter outputs 330W of power to the LED lamp, the Converter input power needs to be around 360W. Nearly 30W of power is lost in the Converter Boost circuit and converted into heat energy, which will also cause the internal temperature of the product machine to rise, affecting the long-term reliability of the product.

[0007] 5. For PD LCD display products larger than 65 inches, the output power of the LED lamp inside the LCD panel is generally above 150W when working. The boost MOS tube, inductor and diode inside the Converter Boost circuit must use high-specification power components and a multi-channel parallel design to meet the design requirements. This will increase the BOM material cost of the LED lamp drive circuit design and reduce the product's market competitiveness. Summary of the invention

[0008] The object of the present invention is to provide a switching power supply circuit of a high-power LED lamp tube which is flicker-free and ultra-quiet and a soft starting method thereof.

[0009] The technical solution adopted by the present invention is:

[0010] A non-flickering ultra-quiet high-power LED lamp switch power supply circuit, which includes an EMI circuit, a bridge rectifier circuit, a PFC boost circuit, a high-voltage large-capacitor filter circuit, a standby circuit, a main substrate circuit, a first main power supply circuit, an OPS / Audio / USB circuit, an overvoltage protection circuit and an LED lamp drive circuit. The city AC power is sequentially connected to the high-voltage large-capacitor filter circuit through the EMI circuit, the bridge rectifier circuit and the PFC boost circuit. The high-voltage large-capacitor filter circuit outputs three high-voltage direct currents to the standby circuit, the first main power supply circuit and the LED lamp drive circuit respectively. The standby circuit outputs a first low-voltage direct current and Vcc1 power supply respectively. voltage, the first low-voltage direct current supplies power to the main substrate circuit, the first main power supply circuit converts the high-voltage direct current into the second low-voltage direct current output, and the second low-voltage direct current supplies power to the open pluggable operating system OPS, the Audio circuit and the USB circuit; the main substrate circuit outputs a standby control signal, a switch signal and a PWM dimming signal; the standby control signal controls the switch of the Vcc1 power supply voltage of the standby circuit; the input end of the overvoltage protection circuit is connected to two overvoltage detection circuits, one overvoltage detection circuit is connected to and detects the first low-voltage direct current, and the other overvoltage detection circuit is connected to and detects the second low-voltage direct current, and the output end of the voltage protection circuit is connected to the standby circuit;

[0011] The LED lamp driving circuit includes a second main power supply circuit, a first reference voltage source circuit, a second reference voltage source circuit, a Vcc2 power supply control circuit, a PWM to DC dimming circuit and a backlight switch control circuit; the Vcc1 power supply voltage is used to power the internal control chip of the first main power supply circuit and the second main power supply circuit, and the high-voltage DC voltage is connected to the primary side of the transformer Tr1 through the second main power supply circuit. The secondary side of the transformer Tr1 has two output windings, and the same-name end of the first output winding is connected to the opposite-name end of the second output winding, and the same-name end of the first output winding is grounded, and the opposite-name end of the first output winding is connected to The anode of the diode D1 and the same-name end of the second output winding are connected to the anode of the diode D2, the cathode of the diode D1 is connected to the input end of the LED lamp tube, the input end of the LED lamp tube is respectively connected to the positive electrode of the electrolytic capacitor C6, the cathode of the diode D2, the negative electrode of the voltage-stabilizing diode ZD1, the resistor R6 and one end of the resistor R11, the second low-voltage direct current is respectively electrically connected to the first reference voltage source circuit, the second reference voltage source circuit, the Vcc2 power supply control circuit and the power supply input end of the backlight switch control circuit, the first reference voltage source circuit outputs a first reference voltage, the second reference voltage source circuit outputs a second reference voltage,

[0012] The switch signals of the main substrate circuit are respectively connected to and control the switch actions of the Vcc2 power supply control circuit and the backlight switch control circuit; the output end of the Vcc2 power supply control circuit is connected to the VCC end of the power supply of the operational amplifier OP1 and the operational amplifier OP2, and the grounding ends of the operational amplifier OP1 and the operational amplifier OP2 are connected to the secondary ground;

[0013] The PWM dimming signal output by the main substrate circuit is connected to the input end of the PWM to DC dimming circuit. The reference end of the PWM to DC dimming circuit is connected to the output end of the first reference voltage source circuit. The PWM to DC dimming circuit converts the PWM dimming signal into a DC dimming signal.

[0014] The first reference voltage is connected to the negative input terminal IN2- of the operational amplifier OP2 and one end of the resistor R12 through the resistor R13, the other end of the resistor R12 is connected to the secondary ground, and the output terminal Out2 of the operational amplifier OP2 is electrically connected to the input port of the overvoltage protection circuit; one end of the resistor R11 is connected to the input end of the LED lamp, and the other end of the resistor R11 is connected to the positive input terminal IN2+ of the operational amplifier OP2 and one end of the resistor R10;

[0015] The output end of the second reference voltage source circuit is connected to the anode of the diode D3, the cathode of the diode D3 is connected to the anode of the Zener diode ZD1, the anode of the Zener diode ZD1 is respectively connected to one end of the resistor R3 and one end of the capacitor C2, the other end of the resistor R3 is connected to the anode of the light-emitting diode inside the optocoupler U3, the other end of the capacitor C2 is connected to the secondary ground, the collector of the photosensitive transistor inside the optocoupler U3 is connected to the feedback end FB of the second main power supply circuit, the emitter of the photosensitive transistor inside the optocoupler U3 is connected to the secondary ground, the cathode of the light-emitting diode inside the optocoupler U3 is connected to the cathode K end of the controllable precision regulator U2 and one end of the resistor R5, the anode A end of the controllable precision regulator U2 is connected to the secondary ground, the other end of the resistor R5 is connected to one end of the capacitor C3, the other end of the resistor R6 is respectively connected to the other end of the capacitor C3, one end of the resistor R8, the reference end R end of the controllable precision regulator U2 and one end of the resistor R7, and the resistor The other end of R7 is connected to the secondary ground, the other end of resistor R8 is connected to the collector of transistor Q2, the emitter of transistor Q2, the other end of resistor R10 and resistor R12 are connected to the secondary ground, the base of transistor Q2 is connected to the output end Out1 of operational amplifier OP1, one end of capacitor C5 and one end of resistor R9, the other end of resistor R9 is connected to one end of capacitor C4, the negative input end IN1- of operational amplifier OP1 is respectively connected to the other end of capacitor C4, the other end of capacitor C5, one end of capacitor C1 and one end of resistor R2, the positive input end IN1+ of operational amplifier OP1 is connected to the output end of PWM to DC dimming circuit, the other end of resistor R2 is respectively connected to the source of MOS tube Q3 and one end of resistor R1, the other end of capacitor C1 and the other end of resistor R1 are connected to the secondary ground, the drain of MOS tube Q1 is connected to the output end of LED lamp tube, the gate of MOS tube Q1 is connected to the output end of backlight switch control circuit,

[0016] Furthermore, the mains AC power uses a 100V~240V mains AC current.

[0017] Furthermore, the operational amplifier OP1 and the operational amplifier OP2 use a dual operational amplifier chip U1 of AS358, and the controllable precision voltage regulator U2 uses TL431; the transistor Q2 is an NPN transistor, and the MOS tube Q1 is an N-channel MOS tube.

[0018] Furthermore, the high voltage direct current is 390V~400V, the first low voltage direct current is 12V / 1.5A, and the second low voltage direct current is 16V / 9A.

[0019] Further, the backlight switch control circuit includes a MOS transistor Q3 and a MOS transistor Q4, the power supply input end of the backlight switch control circuit is respectively connected to one end of a resistor R15 and a resistor R17, the other end of the resistor R15 is respectively connected to the drain of the MOS transistor Q3, one end of the resistor R16 and the gate of the MOS transistor Q4, the base of the MOS transistor Q3 is connected to the switch signal through the resistor R14, the other end of the resistor R17 is respectively connected to the drain of the MOS transistor Q4 and one end of the resistor R18, the source of the MOS transistor Q3, the other end of the resistor R16, the source of the MOS transistor Q4 and the other end of the resistor R18 are connected to the secondary ground, and the drain of the MOS transistor Q4 is led out as the output end of the backlight switch control circuit;

[0020] Among them, the MOS tube Q3 and the MOS tube Q4 are both N-channel MOS tubes, and both are MOS tubes of model 2N7002, and the corresponding gate-source withstand voltage limit value Vgs(max)=20V.

[0021] Further, the Vcc2 power supply control circuit includes a MOS tube Q5, a transistor Q6, and a transistor Q7. The input end of the Vcc2 power supply control circuit is connected to one end of the resistor R21 and the emitter of the transistor Q6. The base of the transistor Q6 is respectively connected to the other end of the resistor R21 and one end of the resistor R20. The other end of the resistor R20 is connected to the drain of the MOS tube Q5. The gate of the MOS tube Q5 receives a switching signal through the resistor R19. The source of the MOS tube Q5 is connected to the secondary ground. The collector of the transistor Q6 is connected to one end of the resistor R22. The other end of the resistor R22 is respectively connected to one end of the resistor R23 and the collector of the transistor Q7. The base of the transistor Q7 is respectively connected to the other end of the resistor R23 and the cathode of the voltage-stabilizing diode ZD2. The emitter of the transistor Q7 is connected to one end of the capacitor C6. The anode of the voltage-stabilizing diode ZD2 and the other end of the capacitor C6 are connected to the secondary ground. The emitter of the transistor Q7 is led out as the output end of the Vcc2 power supply control circuit.

[0022] Among them, transistor Q6 is a PNP transistor, transistor Q7 is an NPN transistor, and MOS tube Q5 is an N-channel MOS tube.

[0023] Furthermore, the first reference voltage source circuit includes a transistor Q8 and a controllable precision voltage regulator U4, the input end of the first reference voltage source circuit is connected to one end of the resistor R24, the other end of the resistor R24 ​​is respectively connected to one end of the resistor R25 and the collector of the transistor Q8, the base of the transistor Q8 is respectively connected to the other end of the resistor R25 and the cathode K end of the controllable precision voltage regulator U4, and the anode A end of the controllable precision voltage regulator U4 is connected to the secondary ground; the emitter of the transistor Q8 is respectively connected to the capacitor C7 and one end of the resistor R26, the other end of the resistor R26 is respectively connected to the reference end R end of the controllable precision voltage regulator U4 and one end of the resistor R27, and the other end of the capacitor C7 and the resistor R27 are connected to the secondary ground; the emitter of the transistor Q8 is led out as the output end of the first reference voltage source circuit.

[0024] Among them, the resistor R26 is selected to be 10KΩ, and the resistor R27 is selected to be 10KΩ.

[0025] Furthermore, the second reference voltage source circuit includes a transistor Q9 and a controllable precision voltage regulator U5, the input end of the second reference voltage source circuit is connected to one end of a resistor R28, the other end of the resistor R28 is respectively connected to one end of a resistor R29 and the collector of the transistor Q9, the base of the transistor Q9 is respectively electrically connected to the other end of the resistor R29 and the cathode K end of the controllable precision voltage regulator U5, and the anode A end of the controllable precision voltage regulator U5 is connected to the secondary ground; the emitter of the transistor Q9 is respectively connected to one end of the capacitor C8 and the resistor R30, the other end of the resistor R30 is respectively connected to the reference end R end of the controllable precision voltage regulator U5 and one end of the resistor R31, and the other end of the capacitor C8 and the resistor R31 is connected to the secondary ground; the emitter of the transistor Q9 is led out as the output end of the second reference voltage source circuit.

[0026] Furthermore, the transistor Q9 is an NPN transistor, the controllable precision voltage regulator U5 adopts TL431, the resistor R30 is selected as 17.8KΩ, and the resistor R31 is selected as 4.7KΩ.

[0027] Further, the PWM to DC dimming circuit includes a MOS transistor Q10 and a MOS transistor Q11, a PWM dimming signal is connected to one end of a resistor R32 through an input end of the PWM to DC dimming circuit, the other end of the resistor R32 is connected to the gate of the MOS transistor Q10, a reference end of the PWM to DC dimming circuit is respectively connected to one end of a resistor R33 and a resistor R34, the other end of the resistor R33 is respectively connected to the drain of the MOS transistor Q10 and the gate of the MOS transistor Q11, the other end of the resistor R34 is respectively connected to the drain of the MOS transistor Q11 and one end of a resistor R35, the other end of the resistor R35 is respectively connected to one end of a capacitor C9 and one end of a resistor R37, the other end of the resistor R37 is connected to one end of a resistor R36, the source of the MOS transistor Q10, the source of the MOS transistor Q11, the other end of the capacitor C9 and the other end of the resistor R36 are connected to the secondary ground, and the other end of the resistor R37 is led out as the output end of the PWM to DC dimming circuit.

[0028] Among them, the resistor R35 is selected as 82KΩ and the capacitor C9 is selected as 0.1uF.

[0029] Furthermore, the first low-voltage direct current output by the standby circuit replaces the second low-voltage direct current output by the first main power supply circuit and is electrically connected to the power supply input terminals of the first reference voltage source circuit, the second reference voltage source circuit, the Vcc2 power supply control circuit and the backlight switch control circuit respectively.

[0030] A soft starting method for a switching power supply circuit of a high-power LED lamp tube without flickering and ultra-quiet, comprising the following steps:

[0031] Step 1, connect to the city AC power, the standby circuit outputs the first low-voltage DC power to the main substrate circuit to work, the main substrate circuit outputs the standby control signal PS_ON as a high-level signal from the first GPIO port to the standby circuit, the standby circuit provides the Vcc1 power supply voltage to the first main power circuit and the second main power circuit, the first main power circuit outputs the second low-voltage DC power to power the OPS / Audio / USB circuit,

[0032] Step 2, after the high level of the standby control signal PS_ON lasts for T1 time, the main substrate circuit outputs the ON / OFF switch signal as high level, the ON / OFF switch signal controls the backlight switch control circuit to turn on the N-channel MOS Q1 to make the output end of the LED lamp tube electrically connected to the current sampling circuit R1, and at the same time the ON / OFF switch signal controls the Vcc2 power supply control circuit to output the power supply voltage to the dual operational amplifier chip U1, wherein T1 time is 20mS time;

[0033] Step 3: After the high level of the ON / OFF switch signal lasts for T2 time, the main substrate circuit outputs a PWM dimming signal with a minimum duty cycle to the PWM to DC dimming circuit.

[0034] Step 4: The PWM to DC dimming circuit gradually increases the PWM dimming duty cycle Duty from the minimum value (such as 20%) to the duty cycle set when the LED lamp works normally after T3 time, wherein T3 time is 50mS time.

[0035] Specifically, the PWM dimming signal is used to have a startup timing with a soft start function, so that the current of the LED lamp tube increases slowly when the lamp is started, and finally reaches the working current required by the LED lamp tube.

[0036] The present invention adopts the above technical solution and has the following characteristics: 1. The traditional Converter Boost LED lamp driving circuit adopts low-frequency PWM dimming of about 100HZ~400HZ, which is easy to cause the screen to easily produce light and dark horizontal stripes interference due to the matching problem between the liquid crystal panel and the screen driving circuit board. The present invention adopts PWM to DC direct current dimming signal to perform analog direct current dimming, which solves the problem of light and dark horizontal stripes interference, and at the same time solves the problem of abnormal sound generated by the boost inductor magnetic component inside the Converter Boost LED lamp driving circuit because the frequency of 100HZ~400HZ is within the audio range received by the human ear. 2. The traditional Converter Boost LED lamp driving circuit adopts a low-frequency PWM dimming signal of about 100HZ~400HZ. Although the human eye cannot perceive the flickering of the LCD screen, when shooting the screen with a mobile phone or a camera, the obvious flickering of the screen will be captured, and it is impossible to achieve a truly flicker-free screen display effect. The present invention uses PWM to DC dimming signal to simulate DC dimming, and the LED lamp current is linear DC. Not only can the human eye not perceive the flickering of the LCD screen, but also there will be no flickering when using a mobile phone or a camera to shoot the screen, which truly achieves the effect of no screen flickering. 3. The conversion efficiency of the traditional Converter Boost LED lamp drive circuit is only between 88% and 93%. The present invention uses the output voltage of the transformer Tr1 to directly drive the LED lamp after the voltage is rectified by the diode D1 / D2 and filtered by the capacitor C6. The conversion efficiency of the Vout2 voltage output by the second main power circuit 91 of the LED lamp drive circuit 9 of the present invention directly drives the LED lamp, which can be designed to be at least 97%, thereby improving the power conversion efficiency of the LED lamp drive circuit in the product power supply, making the product more energy-saving and power-saving. At the same time, due to the improvement of the overall conversion efficiency of the power supply circuit inside the product, the internal ambient temperature of the machine is reduced, which is conducive to improving the reliability of the liquid crystal display product and making the liquid crystal display product more energy-saving and power-saving. 4. The traditional design is that the output voltage of transformer Tr11 is rectified by diodes D1 / D2 and filtered by capacitor C6 to generate a 24V DC power, and then boosted by Converter Boost LED lamp driving circuit, such as generating 66V DC power for LED lamp operation. The LED lamp driving circuit of the present invention uses the output voltage of transformer Tr11 to directly drive the LED lamp after being rectified by diodes D1 / D2 and filtered by capacitor C6, eliminating the traditional Converter Boost LED lamp driving circuit, reducing the BOM material cost price of PD high-power power supply board, and helping to improve the market competitiveness of products. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments;

[0038] Figure 1 It is a schematic diagram of the circuit function blocks of a traditional high-power power supply board inside a 65-inch PD liquid crystal display product in the prior art;

[0039] Figure 2 It is a structural schematic diagram of Embodiment 1 of a switching power supply circuit of a high-power LED lamp tube without flickering and ultra-quiet according to the present invention;

[0040] Figure 3 is a schematic structural diagram of a second reference voltage source circuit according to embodiment 1 of the present invention;

[0041] Figure 4 is a schematic structural diagram of a first reference voltage source circuit according to embodiment 1 of the present invention;

[0042] Figure 5 This is a schematic diagram of the structure of the VCC2 power supply control circuit of Example 1 of the present invention;

[0043] Figure 6 Schematic diagram of the structure of the backlight switch control circuit of Embodiment 1 of the present invention;

[0044] Figure 7 Schematic diagram of the structure of the PWM to DC dimming circuit according to Embodiment 1 of the present invention;

[0045] Figure 8 A schematic diagram of the waveform of the switching power supply circuit of the present invention driven by the existing conventional timing;

[0046] Fig. 9 The schematic diagram of the driving timing of the dimming DIM of the switching power supply circuit of the present invention with soft start;

[0047] Fig.10 It is a structural schematic diagram of Embodiment 2 of a switching power supply circuit of a flicker-free and ultra-quiet high-power LED lamp tube of the present invention. DETAILED DESCRIPTION

[0048] 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.

[0049] like Figures 2 to 10As shown in one, the present invention discloses a switching power supply circuit of a high-power LED lamp tube with no flicker and ultra-quiet, which includes: an EMI circuit, a bridge rectifier circuit, a PFC boost circuit, a high-voltage large-capacitor filter circuit, a standby circuit, a main substrate circuit, a first main power supply circuit, an OPS / Audio / USB circuit, an overvoltage protection circuit and an LED lamp tube drive circuit. The city AC power is electrically connected to the high-voltage large-capacitor filter circuit through the EMI circuit, the bridge rectifier circuit and the PFC boost circuit in sequence. The high-voltage large-capacitor filter circuit outputs three high-voltage direct currents to the standby circuit, the first main power supply circuit and the LED lamp tube drive circuit respectively. The standby circuit outputs a first low-voltage direct current and Vcc1 power supply voltage, the first low-voltage direct current powers the main substrate circuit, the first main power supply circuit converts the high-voltage direct current into the second low-voltage direct current output, and the second low-voltage direct current powers the open pluggable operating system OPS, the Audio circuit and the USB circuit; the main substrate circuit outputs a standby control signal, a switch signal and a PWM dimming signal; the standby control signal controls the switch of the Vcc1 power supply voltage of the standby circuit; the input end of the overvoltage protection circuit is connected to two overvoltage detection circuits, one overvoltage detection circuit is connected to and detects the first low-voltage direct current, and the other overvoltage detection circuit is connected to and detects the second low-voltage direct current, and the output end of the voltage protection circuit is connected to the standby circuit;

[0050] The LED lamp driving circuit includes a second main power supply circuit, a first reference voltage source circuit, a second reference voltage source circuit, a Vcc2 power supply control circuit, a PWM to DC dimming circuit and a backlight switch control circuit;

[0051] The Vcc1 power supply voltage powers the internal control chip of the first main power supply circuit and the second main power supply circuit. The high-voltage direct current voltage is connected to the primary side of the transformer Tr1 through the second main power supply circuit. The secondary side of the transformer Tr1 has two output windings. The same-name end of the first output winding is connected to the opposite-name end of the second output winding, and the same-name end of the first output winding is grounded. The opposite-name end of the first output winding is connected to the anode of the diode D1, and the same-name end of the second output winding is connected to the anode of the diode D2. The cathode of the diode D1 is connected to the input end of the LED lamp tube. The input end of the LED lamp tube is respectively connected to the positive electrode of the electrolytic capacitor C6, the cathode of the diode D2, the negative electrode of the voltage-stabilizing diode ZD1, the resistor R6 and one end of the resistor R11. The second low-voltage direct current is respectively electrically connected to the first reference voltage source circuit, the second reference voltage source circuit, the Vcc2 power supply control circuit and the power supply input end of the backlight switch control circuit. The first reference voltage source circuit outputs a first reference voltage, and the second reference voltage source circuit outputs a second reference voltage.

[0052] The switch signals of the main substrate circuit are respectively connected to and control the switch actions of the Vcc2 power supply control circuit and the backlight switch control circuit; the output end of the Vcc2 power supply control circuit is connected to the VCC end of the power supply of the operational amplifier OP1 and the operational amplifier OP2, and the grounding ends of the operational amplifier OP1 and the operational amplifier OP2 are connected to the secondary ground;

[0053] The PWM dimming signal output by the main substrate circuit is connected to the input end of the PWM to DC dimming circuit. The reference end of the PWM to DC dimming circuit is connected to the first reference voltage. The PWM to DC dimming circuit converts the PWM dimming signal into a DC dimming signal. The first reference voltage is connected to the negative input end IN2- of the operational amplifier OP2 and one end of the resistor R12 through the resistor R13. The other end of the resistor R12 is connected to the secondary ground. The output end Out2 of the operational amplifier OP2 is electrically connected to the input port of the overvoltage protection circuit; one end of the resistor R11 is connected to the input end of the LED lamp tube, and the other end of the resistor R11 is connected to the positive input end IN2+ of the operational amplifier OP2 and one end of the resistor R10 respectively;

[0054] The output end of the second reference voltage source circuit is connected to the anode of the diode D3, the cathode of the diode D3 is connected to the anode of the Zener diode ZD1, the anode of the Zener diode ZD1 is respectively connected to one end of the resistor R3 and one end of the capacitor C2, the other end of the resistor R3 is connected to the anode of the light-emitting diode inside the optocoupler U3, the other end of the capacitor C2 is connected to the secondary ground, the collector of the photosensitive transistor inside the optocoupler U3 is connected to the feedback end FB of the second main power supply circuit, the emitter of the photosensitive transistor inside the optocoupler U3 is connected to the secondary ground, the cathode of the light-emitting diode inside the optocoupler U3 is connected to the cathode K end of the controllable precision regulator U2 and one end of the resistor R5, the anode A end of the controllable precision regulator U2 is connected to the secondary ground, the other end of the resistor R5 is connected to one end of the capacitor C3, the other end of the resistor R6 is respectively connected to the other end of the capacitor C3, one end of the resistor R8, the reference end R end of the controllable precision regulator U2 and one end of the resistor R7, and the resistor The other end of R7 is connected to the secondary ground, the other end of the resistor R8 is connected to the collector of the transistor Q2, the emitter of the transistor Q2, the resistor R10 and the other end of the resistor R12 are connected to the secondary ground, the base of the transistor Q2 is connected to the output end Out1 of the operational amplifier OP1, one end of the capacitor C5 and one end of the resistor R9, the other end of the resistor R9 is connected to one end of the capacitor C4, the negative input end IN1- of the operational amplifier OP1 is respectively connected to the other end of the capacitor C4, the other end of the capacitor C5, one end of the capacitor C1 and one end of the resistor R2, the positive input end IN1+ of the operational amplifier OP1 is connected to the output end of the PWM to DC dimming circuit, the other end of the resistor R2 is respectively connected to the source of the MOS tube Q3 and one end of the resistor R1, the other end of the capacitor C1 and the other end of the resistor R1 are connected to the secondary ground, the drain of the MOS tube Q1 is connected to the output end of the LED lamp tube, and the gate of the MOS tube Q1 is connected to the output end of the backlight switch control circuit.

[0055] Furthermore, the mains AC power uses a 100V~240V mains AC current.

[0056] Furthermore, the operational amplifier OP1 and the operational amplifier OP2 use a dual operational amplifier chip U1 of AS358, and the controllable precision voltage regulator U2 uses TL431; the transistor Q2 is an NPN transistor, and the MOS tube Q1 is an N-channel MOS tube.

[0057] Furthermore, the high voltage direct current is 390V~400V, the first low voltage direct current is 12V / 1.5A, and the second low voltage direct current is 16V / 9A.

[0058] Further, the backlight switch control circuit includes a MOS transistor Q3 and a MOS transistor Q4, the power supply input end of the backlight switch control circuit is respectively connected to one end of a resistor R15 and a resistor R17, the other end of the resistor R15 is respectively connected to the drain of the MOS transistor Q3, one end of the resistor R16 and the gate of the MOS transistor Q4, the base of the MOS transistor Q3 is connected to the switch signal through the resistor R14, the other end of the resistor R17 is respectively connected to the drain of the MOS transistor Q4 and one end of the resistor R18, the source of the MOS transistor Q3, the other end of the resistor R16, the source of the MOS transistor Q4 and the other end of the resistor R18 are connected to the secondary ground, and the drain of the MOS transistor Q4 is led out as the output end of the backlight switch control circuit;

[0059] Among them, the MOS tube Q3 and the MOS tube Q4 are both N-channel MOS tubes, and both are MOS tubes of model 2N7002, and the corresponding gate-source withstand voltage limit value Vgs(max)=20V.

[0060] Further, the Vcc2 power supply control circuit includes a MOS tube Q5, a transistor Q6, and a transistor Q7. The input end of the Vcc2 power supply control circuit is connected to one end of the resistor R21 and the emitter of the transistor Q6. The base of the transistor Q6 is respectively connected to the other end of the resistor R21 and one end of the resistor R20. The other end of the resistor R20 is connected to the drain of the MOS tube Q5. The gate of the MOS tube Q5 receives a switching signal through the resistor R19. The source of the MOS tube Q5 is connected to the secondary ground. The collector of the transistor Q6 is connected to one end of the resistor R22. The other end of the resistor R22 is respectively connected to one end of the resistor R23 and the collector of the transistor Q7. The base of the transistor Q7 is respectively connected to the other end of the resistor R23 and the cathode of the voltage-stabilizing diode ZD2. The emitter of the transistor Q7 is connected to one end of the capacitor C6. The anode of the voltage-stabilizing diode ZD2 and the other end of the capacitor C6 are connected to the secondary ground. The emitter of the transistor Q7 is led out as the output end of the Vcc2 power supply control circuit.

[0061] Among them, the transistor Q6 is a PNP transistor, the transistor Q7 is an NPN transistor, and the MOS transistor Q5 is an N-channel MOS transistor.

[0062] Furthermore, the first reference voltage source circuit includes a transistor Q8 and a controllable precision voltage regulator U4, the input end of the first reference voltage source circuit is connected to one end of the resistor R24, the other end of the resistor R24 ​​is respectively connected to one end of the resistor R25 and the collector of the transistor Q8, the base of the transistor Q8 is respectively connected to the other end of the resistor R25 and the cathode K end of the controllable precision voltage regulator U4, and the anode A end of the controllable precision voltage regulator U4 is connected to the secondary ground; the emitter of the transistor Q8 is respectively connected to the capacitor C7 and one end of the resistor R26, the other end of the resistor R26 is respectively connected to the reference end R end of the controllable precision voltage regulator U4 and one end of the resistor R27, and the other end of the capacitor C7 and the resistor R27 are connected to the secondary ground; the emitter of the transistor Q8 is led out as the output end of the first reference voltage source circuit.

[0063] Among them, the resistor R26 is selected to be 10KΩ, and the resistor R27 is selected to be 10KΩ.

[0064] Furthermore, the second reference voltage source circuit includes a transistor Q9 and a controllable precision voltage regulator U5, the input end of the second reference voltage source circuit is connected to one end of a resistor R28, the other end of the resistor R28 is respectively connected to one end of a resistor R29 and the collector of the transistor Q9, the base of the transistor Q9 is respectively electrically connected to the other end of the resistor R29 and the cathode K end of the controllable precision voltage regulator U5, and the anode A end of the controllable precision voltage regulator U5 is connected to the secondary ground; the emitter of the transistor Q9 is respectively connected to one end of the capacitor C8 and the resistor R30, the other end of the resistor R30 is respectively connected to the reference end R end of the controllable precision voltage regulator U5 and one end of the resistor R31, and the other end of the capacitor C8 and the resistor R31 is connected to the secondary ground; the emitter of the transistor Q9 is led out as the output end of the second reference voltage source circuit.

[0065] Furthermore, the transistor Q9 is an NPN transistor, the controllable precision voltage regulator U5 adopts TL431, the resistor R30 is selected as 17.8KΩ, and the resistor R31 is selected as 4.7KΩ.

[0066] Furthermore, the PWM to DC dimming circuit includes a MOS transistor Q10 and a MOS transistor Q11. The PWM dimming signal is connected to one end of a resistor R32 through an input end of the PWM to DC dimming circuit. The other end of the resistor R32 is connected to the gate of the MOS transistor Q10.

[0067] The reference end of the PWM-to-DC dimming circuit is respectively connected to one end of the resistor R33 and the resistor R34, the other end of the resistor R33 is respectively connected to the drain of the MOS tube Q10 and the gate of the MOS tube Q11, the other end of the resistor R34 is respectively connected to the drain of the MOS tube Q11 and one end of the resistor R35, the other end of the resistor R35 is respectively connected to one end of the capacitor C9 and one end of the resistor R37, the other end of the resistor R37 is connected to one end of the resistor R36, the source of the MOS tube Q10, the source of the MOS tube Q11, the other end of the capacitor C9 and the other end of the resistor R36 are connected to the secondary ground, and the other end of the resistor R37 is led out as the output end of the PWM-to-DC dimming circuit.

[0068] Among them, the resistor R35 is selected as 82KΩ and the capacitor C9 is selected as 0.1uF.

[0069] Furthermore, the first low-voltage direct current output by the standby circuit replaces the second low-voltage direct current output by the first main power supply circuit and is electrically connected to the power supply input terminals of the first reference voltage source circuit, the second reference voltage source circuit, the Vcc2 power supply control circuit and the backlight switch control circuit respectively.

[0070] like Fig. 9 As shown, the present invention also discloses a soft starting method for a switching power supply circuit of a high-power LED lamp tube without flickering and ultra-quiet, which comprises the following steps:

[0071] Step 1, connect to the city AC power, the standby circuit outputs the first low-voltage DC power to the main substrate circuit to work, the main substrate circuit outputs the standby control signal PS_ON as a high-level signal from the first GPIO port to the standby circuit, the standby circuit provides the Vcc1 power supply voltage to the first main power circuit and the second main power circuit, the first main power circuit outputs the second low-voltage DC power to power the OPS / Audio / USB circuit,

[0072] Step 2, after the high level of the standby control signal PS_ON lasts for T1 time, the main substrate circuit outputs the ON / OFF switch signal as high level, the ON / OFF switch signal controls the backlight switch control circuit to turn on the N-channel MOS Q1 to make the output end of the LED lamp tube electrically connected to the current sampling circuit R1, and at the same time the ON / OFF switch signal controls the Vcc2 power supply control circuit to output the power supply voltage to the dual operational amplifier chip U1, wherein T1 time is 20mS time;

[0073] Step 3: After the high level of the ON / OFF switch signal lasts for T2 time, the main substrate circuit outputs a PWM dimming signal with a minimum duty cycle to the PWM to DC dimming circuit.

[0074] Step 4: The PWM to DC dimming circuit gradually increases the PWM dimming duty cycle Duty from the minimum value (such as 20%) to the duty cycle set when the LED lamp works normally after T3 time, wherein T3 time is 50mS time.

[0075] The PWM dimming signal is used to provide a startup timing sequence with a soft start function, so that the current of the LED lamp tube increases slowly when the lamp is started, and finally reaches the working current required by the LED lamp tube.

[0076] The working principle of specific embodiment 1 of the present invention is described in detail below:

[0077] like Figure 2As shown, the switching power supply of the present invention comprises: EMI filter circuit 1, bridge rectifier circuit 2, PFC boost circuit 3, high-voltage large-capacitor filter circuit 4, standby circuit 5, main substrate circuit 6, first main power circuit 7, OPS / Audio / USB circuit 8, LED lamp drive circuit 9, overvoltage protection circuit 10, overvoltage detection circuit 1, overvoltage detection circuit 2. The AC input port of the power board of the LED lamp drive circuit receives a 220V / 50HZ city AC current, which is filtered by the EMI filter circuit 1 and then full-wave rectified by the bridge rectifier circuit 2. The PFC boost circuit 3 receives the pulsating DC voltage output by the bridge rectifier circuit 2 and boosts it, and then filters it by the high-voltage large-capacitor filter circuit 4 to generate a DC voltage of about 390V~400V. The DC power of about 390V~400V is provided to the standby circuit 5 for voltage conversion to output the first DC voltage Vout such as: 12V low-voltage DC The 390V-400V DC power is supplied to the first main power supply circuit 7 for voltage conversion to output a second DC voltage Vout1 such as 16V or 18V low-voltage DC power to power the open pluggable operating system OPS, Audio circuit, USB circuit and other circuits. The 390V-400V DC power is supplied to the second main power supply circuit 91, which is converted by the transformer Tr1, rectified by the D1 / D2 rectifier diodes and filtered by the C6 capacitor to generate a voltage Vout2 required by the LED lamp 95. The standby circuit 5 receives a PS_ON signal from the first GPIO port (GPIO port: abbreviated as a general-purpose input and output interface, which can generally output high and low level signals or PWM pulse width modulation signals through software settings) of the image processor (Scaler) inside the main substrate circuit 6. When the AC power is input and the machine is turned on or enters normal operation in the standby state, the PS_ON signal is a high level signal. The standby circuit 5 provides the Vcc1 power supply voltage to the internal control chip of the first main power circuit 7 and the second main power circuit 91. When the LCD product enters the standby mode, the main substrate circuit Circuit 6 outputs a PS_ON low-level signal, and the Vcc1 power supply voltage stops supplying power to the first main power circuit 7 and the second main power circuit 91 internal control chip, ensuring that the LCD product is more energy-saving and power-saving when in standby mode; the overvoltage protection circuit 10 receives the output signal of the overvoltage detection circuit 1, and when the standby circuit 5 has an abnormal voltage increase in the Vout voltage output due to a short circuit or an open circuit in the feedback sampling resistor inside the circuit, the voltage detection circuit 1 outputs a high-level signal to the overvoltage protection circuit 10, and the overvoltage protection circuit 10 starts the protection mechanism to allow the standby circuit 5 to enter the overvoltage protection mode;When the first main power circuit 7 has an abnormal voltage increase in the Vout1 voltage output due to a short circuit or an open circuit in the feedback sampling resistor inside the circuit, the voltage detection circuit 2 outputs a high level signal to the overvoltage protection circuit 10, and the overvoltage protection circuit 10 activates the protection mechanism to allow the first main power circuit 7 to enter the overvoltage protection mode; when the second main power circuit 91 has an abnormal voltage increase in the Vout2 voltage output due to a short circuit or an open circuit in the feedback sampling resistor inside the circuit, the output terminal Out2 of the second operational amplifier OP2 of the dual operational amplifier chip U1 inside the LED lamp driving circuit 9 outputs a high level signal to the overvoltage protection circuit 10, and the overvoltage protection circuit 10 activates the protection mechanism to allow the second main power circuit 91 to enter the overvoltage protection mode. ;

[0078] The power supply pin of the control chip inside the second main power supply circuit 91 receives the Vcc1 power supply voltage provided by the standby circuit 5. The second main power supply circuit 91 receives a 390V~400V high voltage direct current outputted from the high voltage large capacitor filter circuit 4. After voltage conversion by the transformer Tr1, the voltage is rectified by the rectifier diodes D1 / D2 and filtered by the capacitor C6 to generate a voltage Vout2 required by the LED lamp tube as the power supply input voltage of the LED lamp tube 95. The output end of the LED lamp tube 95 is electrically connected to the drain of an N-channel MOS tube Q1. The gate of the N-channel MOS transistor Q1 is electrically connected to the output port 973 of the backlight switch control circuit 97, the power supply input port 972 of the backlight switch control circuit 97 is electrically connected to the output end of the first main power supply circuit 7 and receives the Vout2 voltage, the port 971 of the backlight switch control circuit 97 receives an ON / OFF switch signal output from the second GPIO port of the image processor (Scaler) inside the main substrate circuit 6, the source of the N-channel MOS transistor Q1 is electrically connected to a current sampling resistor R1 and one end of the resistor R2, the other end of the resistor R1 is connected to the secondary ground, and the other end of the resistor R2 is connected to the secondary ground. It is electrically connected to one end of capacitor C1, the negative input terminal IN1- of the operational amplifier OP1 (abbreviated as operational amplifier OP1) inside the dual operational amplifier chip U1, one end of capacitor C4, and one end of capacitor C5. The other end of capacitor C1 is connected to the secondary ground. The other end of capacitor C4 is electrically connected to one end of resistor R9. The other end of resistor R9 is electrically connected to the other end of capacitor C5, the output terminal Out1 of the operational amplifier OP1 inside the dual operational amplifier chip U1, and the base of NPN transistor Q2. The emitter of NPN transistor Q2 is connected to the secondary ground. The collector of NPN transistor Q2 is electrically connected to one end of resistor R8. The other end of resistor R8 is connected to the controllable precision regulator U2. The reference R end of (such as TL431), one end of the resistor R7, one end of the resistor R6, and one end of the capacitor C3 are electrically connected, the other end of the resistor R7 is connected to the secondary ground, the other end of the resistor R6 is electrically connected to the negative end of the voltage zener diode ZD1 and the positive end of the electrolytic capacitor C6, the positive end of the voltage zener diode ZD1 is electrically connected to the negative end of the diode D3, one end of the capacitor C2, and one end of the resistor R3, the other end of the capacitor C2 is connected to the secondary ground, the positive end of the diode D3 is electrically connected to the output end 922 of the second reference voltage source circuit 92, the input end 921 of the second reference voltage source circuit 92 is electrically connected to the output end of the first main power supply circuit 7 and receives Vout 1 voltage, the other end of the resistor R3 is electrically connected to the positive end of the secondary-side input light-emitting diode of the photocoupler (abbreviated as: photocoupler, Photo-Coupler) U3, the negative end of the secondary-side input light-emitting diode of the photocoupler U3 is electrically connected to one end of the resistor R5 and the cathode K end of the controllable precision regulator U2, the other end of the resistor R5 is electrically connected to the other end of the capacitor C3, the anode A end of the controllable precision regulator U2 is connected to the secondary ground, the collector of the phototransistor at the output end of the photocoupler U3 is electrically connected to the feedback input port 911 of the second main power supply circuit 91, and the emitter of the phototransistor at the output end of the photocoupler U3 is connected to the primary ground.An input port 962 of the PWM to DC dimming circuit 96 receives a reference voltage source Vref1 output from an output port 932 of the first reference voltage source circuit 93, such as Vref1=5V. Another input port 963 of the PWM to DC dimming circuit 96 receives a PWM dimming signal output from a third GPIO port of the main substrate circuit 6. The output terminal 961 of the PWM to DC dimming circuit 96 is electrically connected to the positive input terminal IN1+ of the operational amplifier OP1 inside the dual operational amplifier chip U1, wherein the resistor R2 and the capacitor C1 are used to generate a sampling voltage after sampling the current of the LED lamp tube 95 by the sampling resistor R1, and the sampling voltage is provided to the negative input terminal IN1- of the operational amplifier OP1 inside the dual operational amplifier chip U1 after the high-frequency interference noise is filtered out, and then the DC dimming signal is compared with the positive input terminal IN1+ of the operational amplifier OP1, thereby controlling the current of the LED lamp tube 95; the capacitors C4, C5 and the resistor R9 are used as a double-pole single-zero frequency compensation, and the resistor R9, the capacitor C5 and the resistor R9 are used as a double-pole single-zero frequency compensation. Capacitors C4 and C5, and the operational amplifier OP1 inside the dual operational amplifier chip U1 form an integration circuit. The integration circuit has a deep negative feedback characteristic, which makes the positive input terminal IN1+ and the negative input terminal IN1- of the operational amplifier OP1 inside the dual operational amplifier chip U1 have a virtual short characteristic, that is: V(IN1+)=V(IN1-); when the NPN transistor Q2 works normally, it works in the amplification area, and together with the feedback pull-down resistor R8 / R7 and the feedback pull-up resistor R6 and other feedback circuits, controls the input voltage Vout2 of the LED lamp tube 95=2.5V+(2.5V / R7+(2.5V-Vce(Q2)) / R8)*R6, where: 2.5V is the reference voltage of the reference R terminal of the controllable precision regulator U2 such as: TL431; Vce(Q2) is the voltage between the collector and the emitter of the NPN transistor Q2.

[0079] Resistor R5 and capacitor C3 are used as a single-pole frequency compensation circuit of the controllable precision regulator TL431 of U2, so that the feedback components such as the optocoupler U3 and the controllable precision regulator U2 form a deep negative feedback circuit, ensuring that the working current of the LED lamp 95 can be quickly adjusted according to the PWM duty cycle Duty of the PWM dimming signal output by the third GPIO output port of the main substrate circuit 6, so as to control the brightness and darkness of the LCD display screen. Resistor R3 is a current limiting resistor of the positive end of the light-emitting diode at the input end of the optocoupler U3.

[0080] The power supply input port 931 of the first reference voltage source circuit 93 is electrically connected to the output end of the first main power supply circuit 7, the output port 932 of the first reference voltage source circuit 93 is electrically connected to one end of the resistor R13, the other end of the resistor R13 is electrically connected to one end of the resistor R12 and the negative input terminal IN2- of the OP2 operational amplifier inside the dual operational amplifier chip U1, the other end of the resistor R12 is connected to the secondary ground, one end of the resistor R11 is electrically connected to the input end of the LED lamp tube 95, the other end of the resistor R11 is electrically connected to the positive input terminal IN2+ of the OP2 operational amplifier inside the dual operational amplifier chip U1 and one end of the resistor R10, the other end of the resistor R10 is connected to the secondary ground, the output terminal Out2 of the OP2 operational amplifier inside the dual operational amplifier chip U1 is electrically connected to the input port 101 of the overvoltage protection circuit 10, the resistor R13 receives a reference voltage Vref1 outputted from the output port 932 of the first reference voltage source circuit 93, and after voltage division by the resistors R13 and R12, it is supplied to the negative input terminal IN2- of the OP2 operational amplifier inside the dual operational amplifier chip U1. ,V(IN2-)=Vref1*R12 / (R12+R13)=5V*10KΩ / (10KΩ+10KΩ)=2.5V, where: Vref1 can be designed as 5V DC, and the resistance values ​​of R12 and R13 can be selected as 10KΩ.

[0081] When the PWM dimming signal PWM duty cycle is the largest, that is: Duty=100%, the maximum working current of LED lamp 95 ILB (max) = 5A (the lamp current is generally set according to the typical value of the lamp current specification in the LCD panel Panel specification book, such as: the typical value of the lamp current specification is 5A, the LED lamp 95 current can be designed to be 5A when the LCD display screen is brightest). When the LCD display screen is brightest, when the current sampling resistor R1=0.1Ω, the voltage across the resistor R1 VR1=ILB (max) * R1=5A*0.1Ω=0.5V; the N-channel MOS tube Q1 works normally in the variable resistance area, that is: the fully turned-on working area. If the on-state internal resistance Rds (Q1) of the MOS tube Q1 is 15mΩ at this time, the voltage Vds (Q1) dropped between the drain and source of the MOS tube Q1 = ILB (max) * Rds(Q1)=5A*15mΩ=0.075V; Each string of lights inside the LED lamp tube 95 is composed of 20 light-emitting diodes, and the maximum forward conduction voltage VF(max)=3.3V. At this time, the voltage across the LED lamp tube 95 VLB(max)=VF(max)*20=3.3V*20=66V. At this time, the voltage at the input end of the LED lamp tube 95 Vout2=VR1+ Vds(Q1)+ VLB(max)=0.5V+0.075V+66V=66.575V. At this time, the Vout2 voltage output by the second main power supply circuit 91 of the LED lamp tube driving circuit 9 directly drives the LED lamp tube with a conversion efficiency u≈ VLB(max)* ILB(max) / ( Vout2* ILB(max))= VLB(max) / Vout2=66V / 66.575V=99.13%, that is, when the duty cycle of the PWM dimming signal PWM is the largest, the conversion efficiency of the output voltage Vout2 of the second main power supply circuit 91 directly driving the LED lamp 95 is about 99.13% (Note: the total power consumption of the first reference voltage source circuit, the second reference voltage source circuit, the Vcc2 power supply control circuit, the PWM to DC dimming circuit and the backlight switch control circuit is less than 0.2%, which can be ignored to simplify the design). Figure 1 The main power circuit 2 outputs Vout3, such as: 24V DC generates 66V voltage and 5A LED lamp current to drive the LED lamp after passing through the Converter Boost circuit. The conversion efficiency of the Converter Boost circuit is generally around 88%~93%.

[0082] Considering that the forward voltage VF of the light-emitting diode inside the LED tube 95 may have temperature drift problems and that Vout2 may have some overshoot problems when the power board is powered on, the overvoltage protection point setting value of the input end of the LED tube 95 is usually about 1.2 times the normal working voltage when the screen is brightest, that is: VLB (OVP) = Vout2 * 1.2 = 66.575V * 1.2 = 79.89V. When the overvoltage detection pull-down sampling resistor R10 of the LED tube 95 is selected as 10KΩ, the overvoltage detection pull-up sampling resistor R11 = VLB (OVP) * R10 / V (IN2-) - R10 = 79.89V * 10KΩ / 2.5V - 10KΩ = 309.56KΩ, and the integer R11 resistor can be selected as a 310KΩ resistor.

[0083] This method uses the operational amplifier OP2 inside the dual operational amplifier chip U1 for precise overvoltage detection, thereby obtaining a very precise overvoltage protection point at the input end of the LED lamp tube, ensuring that when the feedback pull-up resistor R6 is open or the pull-down resistor R7 is short-circuited, or the male PIN connector of the LED lamp tube 95 and the female PIN connector of the LED lamp tube 95 on the power board are loose and open, etc., precise and fast overvoltage protection is performed to ensure that when the voltage Vout2 at the input end of the LED lamp tube becomes abnormally high, it will not cause problems such as burning of parts such as the LED lamp tube 95, the N-channel MOS Q1, and the R1 resistor;

[0084] Since the VKA between the cathode and anode of the controllable precision voltage regulator U2 (such as TL431) is relatively low, such as the ultimate withstand voltage VKA(max) of TL431 VKA is only 40V, if the maximum operating voltage VLB(max) of the LED lamp tube 95 is 66V, then the voltage Vout2 at the input end of the LED lamp tube 95 is 66.575V, and the overvoltage protection point VLB(OVP) at the input end of the LED lamp tube 95 is 79.89V=VZD1+R3*IKA+VF(U3)+VKA(U2), where VKA(U2)=VKA(max)*80%=40V*80%=32V (generally 80% design margin is reserved). VF(U3) is the forward conduction voltage of the light-emitting diode at the input end of the optocoupler U3, which is about 1.2V; IKA is the operating current between the cathode and anode of the controllable precision voltage regulator U2, which is about 0.5mA; the resistor R3 can be selected as 3.3KΩ.

[0085] Then, the selected voltage value of the ZD1 Zener diode is VZD1=79.89V-3.3KΩ*0.5mA-1.2V-32V=45.04V. You can select a Zener diode with a voltage value of 45V. If the voltage value of a single Zener diode is not enough, you can use two Zener diodes, such as Zener diodes with voltage values ​​of 27V and 18V, which can be connected in series in sequence. This design can avoid the problem of damage between the cathode and anode of the controllable precision voltage regulator U2 due to insufficient voltage resistance.

[0086] The function of the second reference voltage source circuit 92 is that when the user turns off the LCD screen through the remote control for a short time and does not enter the standby mode, at this time, the PS_ON signal output by the first GPIO port of the image processor (Scaler) inside the main substrate circuit 6 is still high, but the ON / OFF switch signal output by the second GPIO port becomes low, and the PWM dimming signal output by the third GPIO port also becomes low. When the ON / OFF switch signal changes from high to low, the output port 973 of the backlight switch control circuit 97 outputs a low signal to the N-channel The gate of the N-channel MOS tube Q1 is turned off, and the drain and source of the N-channel MOS tube Q1 are in a cut-off state. At the same time, the output port 942 of the Vcc2 power supply control circuit 94 also stops supplying power to the Vcc pin of the dual operational amplifier chip U1. The dual operational amplifier chip U1 stops working, so that the base of the NPN transistor Q2 cannot get the driving current and is in a cut-off state. If the resistor R6=180KΩ, the resistor R7=10KΩ, and the resistor R8=10KΩ, because the NPN transistor Q2 is not turned on, the voltage between the collector and the emitter of the NPN transistor Q2 Vce(Q2)=2.5V (2.5V is the reference voltage of the R terminal of the controllable precision regulator U2 (TL431))

[0087] Vout2=2.5V+(2.5V / R7+(2.5V-Vce(Q2)) / R8)*R6

[0088] =2.5V+(2.5V / 10KΩ+(2.5V-2.5V)) / 10KΩ)*180KΩ

[0089] =47.5V

[0090] The voltage value of the ZD1 Zener diode is 45V, so the voltage VKA dropped between the cathode and anode of the controllable precision regulator U2 = Vout2-VZD1- R3*IKA+VF(U3)=47.5V-45V-3.3KΩ*0.5mA-1.2V=-0.35V

[0091] Among them: VF(U3) is the forward conduction voltage of the light-emitting diode at the input end of the optocoupler U3, which is about 1.2V; IKA is the operating current between the cathode and anode of the controllable precision regulator U2, which is about 0.5mA; the resistor R3 can be selected to be 3.3KΩ.

[0092] The VKA voltage of the controllable precision voltage regulator U2 to ensure normal operation must be at least greater than the 2.5V reference voltage of the reference terminal R. Therefore, when the user turns off the LCD display screen through the remote control for a short time and does not enter the standby mode, the output port 922 of the second reference voltage source 92 will output a direct current of about 12V through the diode D3 to supply power to the cathode K terminal of the controllable precision voltage regulator U2. Therefore, at this time, VKA=12V-VF(D3)-3.3KΩ*0.5mA-1.2V=12V-0.7V-1.65V-1.2V=8.45V>2.5V.

[0093] The second reference voltage source circuit 92, the first reference voltage source circuit 93, the Vcc2 power supply control circuit 94, the backlight switch control circuit 97 and the PWM to DC dimming circuit 96 are all relatively mature circuits, so only a simple description of the working principles of these circuits is given below.

[0094] like Figure 3 As shown, one end of the resistor R28 in the second reference voltage source circuit 92 is electrically connected to the port 921, the other end of the resistor R28 is electrically connected to one end of the resistor R29 and the collector of the NPN transistor Q9, the base of the NPN transistor Q9 is electrically connected to the other end of the resistor R29 and the cathode K end of the controllable precision regulator U5 (such as: TL431), the emitter of the NPN transistor Q9 is electrically connected to one end of the resistor R30, one end of the capacitor C8, and the port 922, the other end of the resistor R30 is electrically connected to the reference end R end of the controllable precision regulator U5 (such as: TL431), and the anode end A end of the controllable precision regulator U5, the other end of the resistor R31, and the other end of the capacitor C8 are connected to the secondary ground. The resistor R28 is a current limiting resistor between the collector and emitter of the NPN transistor Q9, the resistor R29 provides a supply voltage greater than 2.5V for the cathode terminal K of the controllable precision voltage regulator U5, the reference terminal R of the controllable precision voltage regulator U5 is a reference voltage of 2.5V, the port 921 receives the output terminal of the first main power supply circuit 7 outputting the direct current Vout1 (such as: Vout1=16V direct current), and after the direct current voltage conversion by the second reference voltage source circuit 92, generates V(D3+)=2.5V*(R30+R31) / R31=12V, wherein: the resistor R30 can be selected as 17.8KΩ, and the resistor R31 can be selected as 4.7KΩ.

[0095] When the user turns off the LCD display screen for a short time through the remote control and does not enter the standby mode, the output port 922 of the second reference voltage source 92 outputs a DC power of about 12V to the cathode K terminal of the controllable precision regulator U2 through the diode D3 for power supply.

[0096] like Figure 4 As shown, one end of the resistor R24 ​​in the first reference voltage source circuit 93 is electrically connected to the port 931, the other end of the resistor R24 ​​is electrically connected to one end of the resistor R25 and the collector of the NPN transistor Q8, the base of the NPN transistor Q8 is electrically connected to the other end of the resistor R25 and the cathode K end of the controllable precision regulator U4 (such as: TL431), the emitter of the NPN transistor Q8 is electrically connected to one end of the resistor R26, one end of the capacitor C7, and the port 932, the other end of the resistor R26 is electrically connected to the reference end R end of the controllable precision regulator U4, and the anode end A end of the controllable precision regulator U4, the other end of the resistor R27, and the other end of the capacitor C7 are connected to the secondary ground. The resistor R24 ​​is a current limiting resistor between the collector and the emitter of the NPN transistor Q8, the resistor R25 provides a supply voltage greater than 2.5V for the cathode terminal K of the controllable precision voltage regulator U4, the reference terminal R of the controllable precision voltage regulator U4 is a reference voltage of 2.5V, the port 931 receives a Vout1 DC voltage outputted from the output terminal of the first main power supply circuit 7, such as 16V DC, and generates a Vref=2.5V*(R26+R27) / R27=5V after the DC voltage conversion by the first reference voltage source circuit 93, wherein the resistor R26 can be selected as 10KΩ, and the resistor R27 can be selected as 10KΩ. The Vref voltage provides a 5V*(1±2%) high-precision voltage source for the overvoltage protection circuit at the input terminal of the PWM to DC dimming circuit 96 and the LED lamp 95 through the ports 962 and 932, respectively.

[0097] like Figure 5As shown, port 941 in the Vcc2 power supply control circuit 94 is electrically connected to the resistor R21 and the emitter of the PNP transistor Q6, the base of the PNP transistor Q6 is electrically connected to the other end of the resistor R21 and one end of the resistor R20, the other end of the resistor R20 is electrically connected to the drain of the N-channel MOS transistor Q5, the gate of the N-channel MOS transistor Q5 is electrically connected to one end of the resistor R19, the other end of the resistor R19 is electrically connected to port 943, the collector of the PNP transistor Q6 is electrically connected to one end of the resistor R22, the other end of the resistor R22 is electrically connected to one end of the resistor R23 and the NP transistor Q6. The collector of the N transistor Q7 is electrically connected, the base of the NPN transistor Q7 is electrically connected to the other end of the resistor R23 and the negative end of the voltage-stabilizing diode ZD2, the emitter of the NPN transistor Q7 is electrically connected to one end of the capacitor C6 and the 942 port, the source of the N-channel MOS tube Q5, the positive electrode of the voltage-stabilizing diode ZD2 and the other end of the capacitor C6 are connected to the secondary ground, and the 941 port receives the Vout1 output from the first main power supply circuit 7, such as a 16V DC power. When the user uses the remote control to turn on the LCD display, the second GPIO port of the main substrate circuit 6 outputs an ON / OFF The high-level switch signal turns on the N-channel MOS Q5 and the PNP transistor Q6, generating a Vcc2 supply voltage Vcc2=V(ZD2)-Vbe(Q7)=10V-0.7V=9.3V, wherein: the voltage regulator diode ZD2 can select a voltage regulator value V(ZD2) of 10V, and when the NPN transistor Q7 is turned on, Vbe(Q7) between the base and the emitter=0.7V. The Vcc2 voltage is provided to the dual operational amplifier chip U1 by the 942 port for power supply. When the user turns off the LCD display screen with the remote control, the second GPIO port of the main substrate circuit 6 outputs an ON / OFF low-level switch signal to turn off the N-channel MOS Q5 and the PNP transistor Q6, so that the LCD screen is more energy-saving and power-saving when it is turned off.

[0098] like Figure 6As shown, in the backlight switch control circuit 97, the port 971 is electrically connected to one end of the resistor R14, the other end of the resistor 14 is electrically connected to the gate of the N-channel MOS transistor Q3, the drain of the N-channel MOS transistor Q3 is electrically connected to one end of the resistor R15, one end of the resistor R16, and the gate of the N-channel MOS transistor Q4, the other end of the resistor R15 is electrically connected to one end of the resistor R17 and the port 972, the other end of the resistor R17 is electrically connected to the drain of the N-channel MOS Q4, one end of the resistor R18, and the port 973, the other end of the resistor R18, the source of the N-channel MOS transistor Q4, the other end of the resistor R16, and the source of the N-channel MOS transistor Q3 are connected to the secondary ground, the N-channel MOS Q3 and Q4 can usually be selected from models such as: 2N7002, the gate and source of which have a withstand voltage limit value Vgs (max) = 20V, and the Q1 N-channel MOS transistor electrically connected to the port 973 can be selected from models such as: YJD45G10A , the voltage limit between the gate and the source is Vgs(max) = 20V, and the 972 port receives the normal working voltage of Vout1, such as 16V. The overvoltage at the output end of Vout1 is usually detected by a voltage regulator diode, and the overvoltage protection Vovp(out1) has poor accuracy and is generally designed between 1.3 and 1.5 times the normal working voltage of Vout1, that is, the overvoltage protection point Vovp(out1) usually falls between 20.8V and 24V. Therefore, the gate end of the N-channel MOS gate of Q4 needs to be divided by resistors R15 and R16, and the gate end of the N-channel MOS gate of Q1 needs to be divided by resistors R17 and R18 to ensure that when the Vout1 outputs an abnormal overvoltage, the gate voltages of the N-channel MOS tubes Q1 and Q4 still have a certain design margin.

[0099] When the user uses the remote control to turn on the LCD display, the second GPIO port of the main substrate circuit 6 outputs an ON / OFF high-level switch signal to turn on the N-channel MOS Q3 and turn off the N-channel MOS Q4. The voltage between the gate and the source of the N-channel MOS tube Q1 is Vgs(Q1)=Vout1*R18 / (R17+R18)=16V*33KΩ / (11KΩ+33KΩ)=12V, and the turn-on voltage Vgs(th) between the gate and the source of YJD45G10A is between 1V and 3V, that is, at this time, the N-channel MOS tube Q1 works in the variable resistance area of ​​the fully turned-on state.

[0100] When the user turns off the LCD display screen with the remote control, the second GPIO port of the main substrate circuit 6 outputs an ON / OFF low-level switch signal to turn off the N-channel MOS Q3 and pass the N-channel MOS Q4. The gate of the N-channel MOS tube Q1 cannot obtain voltage and is in a completely cut-off state. Therefore, the N-channel MOS tube Q1 electrically connected to the output end of the LED lamp tube 95 only acts as a switch in this circuit. When the LCD display screen is turned off, the current of the LED lamp tube 95 is completely cut off, ensuring that the screen is in a completely black state after the LCD display screen is turned off.

[0101] like Figure 7 As shown, port 963 in the PWM-to-DC dimming circuit 96 is electrically connected to one end of the resistor R32, the other end of the resistor R32 is electrically connected to the gate of the N-channel MOS transistor Q10, the drain of the N-channel MOS transistor Q10 is electrically connected to one end of the resistor R33 and the gate of the N-channel MOS transistor Q11, the drain of the N-channel MOS transistor Q11 is electrically connected to one end of the resistor R34 and one end of the resistor R35, the other end of the resistor R34 is electrically connected to the other end of the resistor R33 and port 962, the other end of the resistor R35 is electrically connected to one end of the capacitor C9 and one end of the resistor R37, the other end of the resistor R37 is electrically connected to one end of the resistor R36 and port 961, and the sources of the N-channel MOS transistors Q10 and Q11, the other end of the capacitor C9, and the other end of the resistor R36 are connected to the secondary ground. When the LCD display is turned on, the 963 port receives the third GPIO port of the main substrate circuit 6 and outputs a high-frequency PWM pulse width modulation signal, such as the PWM frequency Fpwm=25KHZ, and the cut-off frequency Fc of the resistor R35 and the capacitor C9 in the RC low-pass filter circuit is 1 / (2*ᴫ*R35*C9)= 1 / (2*3.14*82KΩ*0.1uF)=19.4HZ, where: resistor R35 can be selected as 82KΩ, capacitor C9 can be selected as 0.1uF, PWM frequency Fpwm is much larger than RC low-pass filter cutoff frequency Fc, so that the PWM dimming signal is low-pass filtered by resistor R35 and capacitor C9 to generate a low-voltage ripple DC dimming signal Vdc, and the Vdc voltage is divided by resistor R36 (such as: resistor R36 can be selected as 15KΩ) and resistor R37 (such as: resistor R37 can be selected as 51KΩ) and then provided by port 961 to the positive input terminal IN1+ of the internal operational amplifier OP1 of the dual operational amplifier chip U1 to adjust the working current of the LED lamp 95. Generally, the value of resistor R34 is small, such as: it can be about 2KΩ, which is much smaller than the resistor R35. The positive input terminal IN1 of the operational amplifier OP1 inside the U1 chip + DC dimming voltage V(IN1+) = Vref1*Duty*R36 / (R34+R35+R36+R37); where Duty is the duty cycle of the PWM dimming signal, which is generally designed to be between 20% and 100%.

[0102] LED lamp 95 current control principle description: when Duty=100%, V(IN1+)=5V*100%*15KΩ / (2KΩ+82KΩ+15KΩ+51KΩ)=0.5V.

[0103] Resistor R9, capacitors C4 and C5, and the internal operational amplifier OP1 of the dual operational amplifier chip U1 form an integration circuit. The circuit has deep negative feedback, so that the positive input terminal IN1+ and the negative input terminal IN1- of the internal operational amplifier OP1 of the dual operational amplifier chip U1 have a virtual short characteristic, that is: V(IN1+)=V(IN1-)=0.5V, and the current sampling resistor R1 can be selected as 0.1Ω. The resistor R2 and the capacitor C1 are used to filter out high-frequency noise voltage.

[0104] At this time, the LED lamp 95 current ILED=VR1 / R1= V(IN1-) / R1=0.5V / 0.1Ω=5A, and the LCD display is the brightest.

[0105] When the PWM dimming signal Duty is adjusted from 100% to 99%, that is, when the user adjusts the LCD display screen from the brightest to a slightly darker one, the duty cycle Duty of the PWM dimming signal output by the third GPIO port of the main substrate circuit 6 decreases, that is: Duty↓, the positive input terminal IN1+ DC dimming voltage V(IN1+)↓=Vref1*Duty↓*R36 / ( R34+R35+R36+R37) of the operational amplifier OP1 inside the dual operational amplifier chip U1 decreases, that is: V(IN1+)↓, at this time V(IN1+)< V(IN1-), the output voltage of the output terminal Out1 of the operational amplifier OP1 inside the dual operational amplifier chip U1 decreases, driving the base current Ibe(Q2)↓ of the NPN transistor Q2, the NPN transistor Q2 works in the amplification area, and the collector current Ice(Q2)↓=Ibe(Q2)↓*β, where β is the amplification factor of the Q2 transistor, The voltage between the collector and emitter of the NPN transistor Q2 is Vce(Q2)↑=2.5V- Ice(Q2)↓*R8, where: 2.5V is the reference voltage of the reference terminal R of the controllable precision voltage regulator U2TL431, so the voltage Vout2 at the input end of the LED lamp tube 95 drops by Vout2↓=2.5V+(2.5V / R7+(2.5V-Vce(Q2)↑) / R8)*R6, and the current of the LED lamp tube 95 drops by ILED↓=Vout2↓ / (R1+Rds(Q1)+ZLED), where Rds(Q1) is the internal resistance between the drain and the source when the N-channel MOS tube Q1 is fully turned on, and ZLED is the equivalent internal resistance when the LED lamp tube is working.

[0106] The negative input voltage of the operational amplifier OP1 inside the dual operational amplifier chip U1 decreases V(IN1-)↓=VR1=ILED↓*R1. When the voltage V(IN1-) decreases to be equal to the positive input voltage V(IN1+) of the operational amplifier OP1 inside the dual operational amplifier chip U1, it will no longer decrease. That is, when the duty cycle Duty of the PWM dimming signal decreases, the current of the LED lamp tube 95 will be adjusted accordingly by the LED lamp tube driving circuit 9 to become smaller. When the user adjusts the brightness of the LCD display to the darkest, the duty cycle Duty of the PWM dimming signal is reduced to 20%. At this time, the positive input voltage V(IN1+) of the operational amplifier OP1 inside the dual operational amplifier chip U1 is 5V*20%*15KΩ / (2KΩ+82KΩ+15KΩ+51KΩ)=0.1V.

[0107] At this time, the current of the LED lamp tube 95 will be adjusted accordingly by the LED lamp tube driving circuit 9 to ILED = V(IN1+) / R1 = 0.1V / 0.1Ω = 1A. Similarly, when the duty cycle Duty of the PWM dimming signal increases, the current of the LED lamp tube 95 will be adjusted accordingly by the LED lamp tube driving circuit 9 and the LCD display screen will become brighter.

[0108] like Figure 8 As shown, the LED lamp driver of the present invention has a large response speed delay problem in the entire LED lamp current feedback circuit, which is easy to generate a large overshoot current Overshoot problem at the input end of the LED lamp 95 when the LCD screen is turned on. For example, a peak overshoot current of up to about 7A is generated during the ΔT time when the LCD screen is turned on, while the normal working current is about 4A. This overshoot current 7A often exceeds the maximum working current of the LED lamp when designed, such as 5A, and even exceeds the upper limit of the withstand current of the light emitting diode inside the LED lamp, so that the light emitting diode chip inside the LED lamp is prone to instantaneous overheating when the LED lamp is turned on, which reduces the reliability and life of the normal use of the LED lamp 95, and even directly burns the light emitting diode chip.

[0109] as follows Fig. 9As shown, the present invention will adopt a power-on timing in which the PWM dimming signal has a soft start function when the LCD screen is turned on. The timing is described as follows: When the city AC power such as 220Vac is connected to the LED lamp driving power board of the present invention, the standby circuit 5 outputs a Vout voltage, such as 12V DC power to the main substrate circuit 6 to work, and the main substrate circuit 6 will output a PS_ON high-level signal from the first GPIO port to the standby circuit 5. The standby circuit provides a Vcc1 power supply voltage to the first main power circuit 7 and the second main power circuit 91. The first main power circuit 7 outputs a Vout1 DC power, such as 16V DC power to power the OPS / Audio / USB and other circuits. After the PS_ON high-level signal is sent out for T1 time, such as 20mS time, the main substrate circuit 6 will output an ON / OFF high-level switch signal from the second GPIO port to the backlight switch control circuit 97 to turn on the N-channel MOS Q1 electrically connects the output end of the LED lamp tube 95 to the current sampling circuit R1, and at the same time sends an ON / OFF high-level switch signal to the Vcc2 power supply control circuit 94, so that the Vcc2 power supply control circuit 94 outputs the Vcc2 power supply voltage required by the dual operational amplifier chip U1 from the 942 port. After the ON / OFF high-level switch signal is output, after T2 time, the main substrate circuit 6 will output a minimum duty cycle (e.g., Duty=20%) PWM dimming signal from the third GPIO port to the PWM to DC dimming circuit 96. After T3 time, such as 50mS time, the PWM dimming duty cycle Duty gradually increases from 20% to the duty cycle set when the LED lamp tube 95 is working normally, such as: PWM Duty=80% set by the user during normal operation, and the working current of the LED lamp tube 95 is 4A.

[0110] The PWM dimming signal has a power-on timing with a soft-start function, so that the current of the LED lamp tube 95 slowly increases when the power is turned on, and finally reaches the working current required by the LED lamp tube 95, such as 4A, to avoid the problem of overshoot of the current of the LED lamp tube 95 at the moment of powering on, which leads to the reduction of the reliability and life of the LED lamp tube 95, or even the direct burning of the light-emitting diode chip.

[0111] The present invention adopts the above technical solution and has the following characteristics: 1. The traditional Converter Boost LED lamp driving circuit adopts low-frequency PWM dimming of about 100HZ~400HZ, which is easy to cause the screen to easily produce light and dark horizontal stripes interference due to the matching problem between the liquid crystal panel and the screen driving circuit board. The present invention adopts PWM to DC direct current dimming signal to perform analog direct current dimming, which solves the problem of light and dark horizontal stripes interference, and at the same time solves the problem of abnormal sound generated by the boost inductor magnetic component inside the Converter Boost LED lamp driving circuit because the frequency of 100HZ~400HZ is within the audio range received by the human ear. 2. The traditional Converter Boost LED lamp driving circuit adopts a low-frequency PWM dimming signal of about 100HZ~400HZ. Although the human eye cannot perceive the flickering of the LCD screen, when shooting the screen with a mobile phone or a camera, the obvious flickering of the screen will be captured, and it is impossible to achieve a truly flicker-free screen display effect. The present invention uses PWM to DC dimming signal to simulate DC dimming, and the LED lamp current is linear DC. Not only can the human eye not perceive the flickering of the LCD screen, but also there will be no flickering when using a mobile phone or a camera to shoot the screen, which truly achieves the effect of no screen flickering. 3. The conversion efficiency of the traditional Converter Boost LED lamp drive circuit is only between 88% and 93%. The present invention uses the output voltage of the transformer Tr11 to directly drive the LED lamp after the voltage is rectified by the diode D1 / D2 and filtered by the capacitor C6. The conversion efficiency of the Vout2 voltage output by the second main power circuit 91 of the LED lamp drive circuit 9 of the present invention directly drives the LED lamp, which can be designed to be at least 97%, thereby improving the power conversion efficiency of the LED lamp drive circuit in the product power supply, making the product more energy-saving and power-saving. At the same time, due to the improvement of the overall conversion efficiency of the power supply circuit inside the product, the internal ambient temperature of the machine is reduced, which is conducive to improving the reliability of the liquid crystal display product and making the liquid crystal display product more energy-saving and power-saving. 4. The traditional design is that the output voltage of transformer Tr11 is rectified by diodes D1 / D2 and filtered by capacitor C6 to generate a 24V DC power, and then boosted by Converter Boost LED lamp driving circuit, such as generating 66V DC power for LED lamp operation. The LED lamp driving circuit of the present invention uses the output voltage of transformer Tr11 to directly drive the LED lamp after being rectified by diodes D1 / D2 and filtered by capacitor C6, eliminating the traditional Converter Boost LED lamp driving circuit, reducing the BOM material cost price of PD high-power power supply board, and helping to improve the market competitiveness of products.

[0112] 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 claimed 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 of the art without making creative work are within the scope of protection of the present application.

Claims

1. A non-flickering ultra-quiet high-power LED lamp switch power supply circuit, which includes an EMI circuit, a bridge rectifier circuit, a PFC boost circuit, a high-voltage large-capacitor filter circuit, a standby circuit, a main substrate circuit, a first main power circuit, an OPS / Audio / USB circuit, an overvoltage protection circuit and an LED lamp drive circuit. The city AC power is sequentially connected to the high-voltage large-capacitor filter circuit through the EMI circuit, the bridge rectifier circuit and the PFC boost circuit. The high-voltage large-capacitor filter circuit outputs three high-voltage direct currents to the standby circuit, the first main power circuit and the LED lamp drive circuit respectively. The standby circuit outputs a first low-voltage direct current and Vcc1 for power supply. The first low-voltage direct current supplies power to the main substrate circuit, the first main power supply circuit converts the high-voltage direct current into the second low-voltage direct current output, and the second low-voltage direct current supplies power to the open pluggable operating system OPS, the Audio circuit and the USB circuit; the main substrate circuit outputs a standby control signal, a switch signal and a PWM dimming signal; the standby control signal controls the switch of the Vcc1 power supply voltage of the standby circuit; the input end of the overvoltage protection circuit is connected to two overvoltage detection circuits, one overvoltage detection circuit is connected to and detects the first low-voltage direct current, and the other overvoltage detection circuit is connected to and detects the second low-voltage direct current, and the output end of the voltage protection circuit is connected to the standby circuit; Features: The LED lamp driving circuit includes a second main power supply circuit, a first reference voltage source circuit, a second reference voltage source circuit, a Vcc2 power supply control circuit, a PWM to DC dimming circuit and a backlight switch control circuit; The Vcc1 power supply voltage powers the internal control chip of the first main power supply circuit and the second main power supply circuit. The high-voltage direct current voltage is connected to the primary side of the transformer Tr1 through the second main power supply circuit. The secondary side of the transformer Tr1 has two output windings. The same-name end of the first output winding is connected to the opposite-name end of the second output winding, and the same-name end of the first output winding is grounded. The opposite-name end of the first output winding is connected to the anode of the diode D1, and the same-name end of the second output winding is connected to the anode of the diode D2. The cathode of the diode D1 is connected to the input end of the LED lamp tube. The input end of the LED lamp tube is respectively connected to the positive electrode of the electrolytic capacitor C6, the cathode of the diode D2, the negative electrode of the voltage-stabilizing diode ZD1, the resistor R6 and one end of the resistor R11. The second low-voltage direct current is respectively electrically connected to the first reference voltage source circuit, the second reference voltage source circuit, the Vcc2 power supply control circuit and the power supply input end of the backlight switch control circuit. The first reference voltage source circuit outputs a first reference voltage, and the second reference voltage source circuit outputs a second reference voltage. The switch signals of the main substrate circuit are respectively connected to and control the switch actions of the Vcc2 power supply control circuit and the backlight switch control circuit; the output end of the Vcc2 power supply control circuit is connected to the VCC end of the power supply of the operational amplifier OP1 and the operational amplifier OP2, and the grounding ends of the operational amplifier OP1 and the operational amplifier OP2 are connected to the secondary ground; The PWM dimming signal output by the main substrate circuit is connected to the input end of the PWM to DC dimming circuit. The reference end of the PWM to DC dimming circuit is connected to the output end of the first reference voltage source circuit. The PWM to DC dimming circuit converts the PWM dimming signal into a DC dimming signal. The first reference voltage is connected to the negative input terminal IN2- of the operational amplifier OP2 and one end of the resistor R12 through the resistor R13, the other end of the resistor R12 is connected to the secondary ground, and the output terminal Out2 of the operational amplifier OP2 is connected to the input port of the overvoltage protection circuit; one end of the resistor R11 is connected to the input end of the LED lamp, and the other end of the resistor R11 is connected to the positive input terminal IN2+ of the operational amplifier OP2 and one end of the resistor R10; The output end of the second reference voltage source circuit is connected to the anode of the diode D3, the cathode of the diode D3 is connected to the anode of the Zener diode ZD1, the anode of the Zener diode ZD1 is respectively connected to one end of the resistor R3 and one end of the capacitor C2, the other end of the resistor R3 is connected to the anode of the light-emitting diode inside the optocoupler U3, the other end of the capacitor C2 is connected to the secondary ground, the collector of the photosensitive transistor inside the optocoupler U3 is connected to the feedback end FB of the second main power supply circuit, the emitter of the photosensitive transistor inside the optocoupler U3 is connected to the secondary ground, the cathode of the light-emitting diode inside the optocoupler U3 is connected to the cathode K end of the controllable precision regulator U2 and one end of the resistor R5, the anode A end of the controllable precision regulator U2 is connected to the secondary ground, and the other end of the resistor R5 is connected to one end of the capacitor C3. The other end of the resistor R6 is respectively connected to the other end of the capacitor C3, one end of the resistor R8, the reference end R of the controllable precision voltage regulator U2 and one end of the resistor R7. The other end of the resistor R7 is connected to the secondary ground. The other end of the resistor R8 is connected to the collector of the transistor Q2, and the emitter of the transistor Q2, the resistor R10 and the other end of the resistor R12 are connected to the secondary ground. The base of transistor Q2 is connected to the output terminal Out1 of operational amplifier OP1, one end of capacitor C5 and one end of resistor R9, the other end of resistor R9 is connected to one end of capacitor C4, the negative input terminal IN1- of operational amplifier OP1 is respectively connected to the other end of capacitor C4, the other end of capacitor C5, one end of capacitor C1 and one end of resistor R2, the positive input terminal IN1+ of operational amplifier OP1 is connected to the output end of PWM to DC dimming circuit, the other end of resistor R2 is respectively connected to the source of MOS tube Q3 and one end of resistor R1, the other end of capacitor C1 and the other end of resistor R1 are connected to secondary ground, the drain of MOS tube Q1 is connected to the output end of LED lamp tube, and the gate of MOS tube Q1 is connected to the output end of backlight switch control circuit.

2. According to claim 1, a flicker-free, ultra-quiet, high-power LED lamp switching power supply circuit, characterized in that: The mains AC power used is 100V~240V mains AC power, the high voltage DC power is 390V~400V, the first low voltage DC power is 12V / 1.5A, and the second low voltage DC power is 16V / 9A.

3. The switching power supply circuit of a flicker-free and ultra-quiet high-power LED lamp according to claim 1, characterized in that: The operational amplifier OP1 and the operational amplifier OP2 use the dual operational amplifier chip U1 of AS358, and the controllable precision voltage regulator U2 uses TL431; the transistor Q2 is an NPN transistor, and the MOS tube Q1 is an N-channel MOS tube.

4. The switching power supply circuit of a flicker-free and ultra-quiet high-power LED lamp according to claim 1, characterized in that: The backlight switch control circuit includes a MOS transistor Q3 and a MOS transistor Q4. The power supply input end of the backlight switch control circuit is respectively connected to one end of a resistor R15 and a resistor R17. The other end of the resistor R15 is respectively connected to the drain of the MOS transistor Q3, one end of the resistor R16 and the gate of the MOS transistor Q4. The base of the MOS transistor Q3 is connected to the switch signal through the resistor R14. The other end of the resistor R17 is respectively connected to the drain of the MOS transistor Q4 and one end of the resistor R18. The source of the MOS transistor Q3, the other end of the resistor R16, the source of the MOS transistor Q4 and the other end of the resistor R18 are connected to the secondary ground. The drain of the MOS transistor Q4 is led out as the output end of the backlight switch control circuit. Among them, the MOS tube Q3 and the MOS tube Q4 are both N-channel MOS tubes, and both are MOS tubes of model 2N7002, and the corresponding gate-source withstand voltage limit value Vgs(max)=20V.

5. The switching power supply circuit of a flicker-free and ultra-quiet high-power LED lamp according to claim 1, characterized in that: The Vcc2 power supply control circuit includes a MOS tube Q5, a transistor Q6 and a transistor Q7. The input end of the Vcc2 power supply control circuit is connected to one end of a resistor R21 and the emitter of the transistor Q6. The base of the transistor Q6 is respectively connected to the other end of the resistor R21 and one end of the resistor R20. The other end of the resistor R20 is connected to the drain of the MOS tube Q5. The gate of the MOS tube Q5 receives a switch signal through a resistor R19. The source of the MOS tube Q5 is connected to the secondary ground. The collector of the transistor Q6 is connected to one end of the resistor R22. The other end of the resistor R22 is respectively connected to one end of the resistor R23 and the collector of the transistor Q7. The base of the transistor Q7 is respectively connected to the other end of the resistor R23 and the cathode of the voltage-stabilizing diode ZD2. The emitter of the transistor Q7 is connected to one end of the capacitor C6. The anode of the voltage-stabilizing diode ZD2 and the other end of the capacitor C6 are connected to the secondary ground. The emitter of the transistor Q7 is led out as the output end of the Vcc2 power supply control circuit.

6. The switching power supply circuit of a flicker-free and ultra-quiet high-power LED lamp according to claim 1, characterized in that: The first reference voltage source circuit includes a transistor Q8 and a controllable precision voltage regulator U4. The input end of the first reference voltage source circuit is connected to one end of a resistor R24, the other end of the resistor R24 ​​is respectively connected to one end of a resistor R25 and the collector of the transistor Q8, the base of the transistor Q8 is respectively connected to the other end of the resistor R25 and the cathode K end of the controllable precision voltage regulator U4, and the anode A end of the controllable precision voltage regulator U4 is connected to the secondary ground; the emitter of the transistor Q8 is respectively connected to one end of the capacitor C7 and the resistor R26, the other end of the resistor R26 is respectively connected to the reference end R end of the controllable precision voltage regulator U4 and one end of the resistor R27, and the other end of the capacitor C7 and the resistor R27 are connected to the secondary ground; the emitter of the transistor Q8 is led out as the output end of the first reference voltage source circuit.

7. The switching power supply circuit of a flicker-free and ultra-quiet high-power LED lamp according to claim 1, characterized in that: The second reference voltage source circuit includes a transistor Q9 and a controllable precision voltage regulator U5, the input end of the second reference voltage source circuit is connected to one end of a resistor R28, the other end of the resistor R28 is respectively connected to one end of a resistor R29 and the collector of the transistor Q9, the base of the transistor Q9 is respectively electrically connected to the other end of the resistor R29 and the cathode K end of the controllable precision voltage regulator U5, and the anode A end of the controllable precision voltage regulator U5 is connected to the secondary ground; The emitter of transistor Q9 is connected to one end of capacitor C8 and resistor R30 respectively, the other end of resistor R30 is connected to the reference end R of controllable precision voltage regulator U5 and one end of resistor R31 respectively, the other end of capacitor C8 and resistor R31 is connected to secondary ground; The emitter of the transistor Q9 is led out as the output terminal of the second reference voltage source circuit.

8. The switching power supply circuit of a flicker-free and ultra-quiet high-power LED lamp according to claim 1, characterized in that: The PWM to DC dimming circuit includes a MOS tube Q10 and a MOS tube Q11. The PWM dimming signal is connected to one end of a resistor R32 through the input end of the PWM to DC dimming circuit. The other end of the resistor R32 is connected to the gate of the MOS tube Q10. The reference end of the PWM-to-DC dimming circuit is respectively connected to one end of the resistor R33 and the resistor R34, the other end of the resistor R33 is respectively connected to the drain of the MOS tube Q10 and the gate of the MOS tube Q11, the other end of the resistor R34 is respectively connected to the drain of the MOS tube Q11 and one end of the resistor R35, the other end of the resistor R35 is respectively connected to one end of the capacitor C9 and one end of the resistor R37, the other end of the resistor R37 is connected to one end of the resistor R36, the source of the MOS tube Q10, the source of the MOS tube Q11, the other end of the capacitor C9 and the other end of the resistor R36 are connected to the secondary ground, and the other end of the resistor R37 is led out as the output end of the PWM-to-DC dimming circuit.

9. The switching power supply circuit of a flicker-free and ultra-quiet high-power LED lamp according to claim 1, characterized in that: The first low-voltage direct current output by the standby circuit replaces the second low-voltage direct current output by the first main power supply circuit and is respectively connected to the power supply input terminals of the first reference voltage source circuit, the second reference voltage source circuit, the Vcc2 power supply control circuit and the backlight switch control circuit.

10. A soft starting method for a switching power supply circuit of a flicker-free ultra-quiet high-power LED lamp tube, using a flicker-free ultra-quiet high-power LED lamp tube switching power supply circuit as claimed in any one of claims 1 to 9, characterized in that: The soft start method includes the following steps: Step 1, connect to the city AC power, the standby circuit outputs the first low-voltage DC power to the main substrate circuit to work, the main substrate circuit outputs the standby control signal PS_ON as a high-level signal from the first GPIO port to the standby circuit, the standby circuit provides the Vcc1 power supply voltage to the first main power circuit and the second main power circuit, the first main power circuit outputs the second low-voltage DC power to power the OPS / Audio / USB circuit, Step 2, after the high level of the standby control signal PS_ON lasts for T1 time, the main substrate circuit outputs the ON / OFF switch signal as high level, the ON / OFF switch signal controls the backlight switch control circuit to turn on the N-channel MOS Q1 to make the output end of the LED lamp tube electrically connected to the current sampling circuit R1, and at the same time the ON / OFF switch signal controls the Vcc2 power supply control circuit to output the power supply voltage to the dual operational amplifier chip U1; Step 3: After the high level of the ON / OFF switch signal lasts for T2 time, the main substrate circuit outputs a PWM dimming signal with a minimum duty cycle to the PWM to DC dimming circuit. Step 4: The PWM to DC dimming circuit gradually increases the PWM dimming duty cycle Duty from the minimum value to the duty cycle set when the LED lamp works normally after T3 time.

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