TWM438012U - Light-emitting diode driving device - Google Patents

Description

M438012 V. New description: [New technology field] [0001] This creation is about a light-emitting diode (Light-Emitting)

Diode, LED) drive circuits, and in particular, an LED drive circuit suitable for high power LED light sources. [Prior Art]

[0002] FIG. 1 is a conventional LED commonly used in large-size liquid crystal display products.

A block diagram of the drive circuit. Referring to FIG. 1, a large-sized liquid crystal display product usually needs to use a high-power LED light source, which is usually composed of LED light strings LB1 LBLBn, and each LED light string includes a plurality of LEDs coupled in series. Where η is a positive integer. When η is larger than 1, these LED strings LB1 to LBn are driven in parallel. The LED driving circuit 1 is for driving the LED light strings LB1 LBLBn, and includes a main power supply circuit 11, a standby power supply circuit 12, a boost conversion circuit 13, constant current source circuits 141 to 14n, an LED feedback control circuit 15, and an LED. Short circuit protection circuit 16 and dimming control circuit 1 7 ^ ® [0003] The LED drive circuit 1 receives a stable DC bus voltage Vbus generated by rectification, power factor correction and filtering of AC mains, typically about 400 volts (volt, V) around. The bus voltage Vbus is stepped down by the main power supply circuit 11 to generate main power voltages Vra 1 and Vm2, for example, 24V and 12V, respectively. The main power supply voltage Vml is used to generate a lamp input voltage Vin which is slightly larger than the required operating voltage of the LED string after being boosted by the boost converter circuit 13, for example, 86V, to be output to the LED lamp strings LB1 LB LBn. Input. The main power supply voltage Vm2 is used to supply power required for liquid crystal display products such as audio circuits and panel drive circuits. Busbar 10120751 癸Single number A〇101 Page 3/Total 23 page 1012024557-0 [0004] M438012 Voltage Vbus is also passed through the standby power supply circuit 丨2 to generate standby power supply voltage Vsb 'for example 5V, for providing The power required for components inside the LCD display such as the motherboard microcontroller that still needs to work in standby mode. The boost converter circuit 13 includes a boost converter, an output filter circuit, and a wheel-out feedback control circuit. Among them, the boost converter includes an inductor L1 as an energy storage element and a transistor qi and a diode di as a switching element for performing boost conversion. The output filter circuit includes a capacitor Ci for reducing the output voltage ripple of the boost converter. The output feedback control circuit includes a Pulse-Width Modulation (PWM) controller U11 for controlling the switching duty cycle of the transistor Q1 according to the output of the LED feedback control circuit 15 to adjust the output voltage of the boost converter. (In this example, the string input voltage Vin). The constant current source circuits 141 to 14n are respectively coupled to the output terminals of the LED lamp strings LB1 to LBn for controlling the LED lamp strings LB1 to LBn to have a constant current and an equal magnitude during operation. Please refer to FIG. 2, which is a circuit diagram of a constant current source circuit commonly used in a three-terminal adjustable shunt regulator. Taking the constant current source circuit 141 as an example, it includes a transistor q2, resistors R1 to R3, and a shunt regulator U21 having an anode terminal A, a cathode terminal K, and a reference terminal R. When the shunt regulator U21 adopts AZ432, it has a reference electric dust source of 1.25V inside, and the reference terminal r voltage will be stable at 丨.25V, so that the operating current Ilbl of the LED string LB1 is constant and its value is Ilbl= l.25V/R1 〇[0005] Please refer to 圊1 and cooperate with Figure 2, if the output voltage of the LED string is too low, then fall between the 汲 and source terminals of the transistor q2 in the constant current source circuit. The pressure drop (hereinafter referred to as the 汲 source voltage drop) will be low and will change from the normal working in the strange flow area to the variable resistance area and cannot be made to the LED string. 10120751#单号A〇101 Page 4/ A total of 23 pages 1012024557-0 M438012 flow control, in which Vgs > Vth and Vds > Vgs-Vth when operating in the constant current region, Vgs > Vth and Vds < Vgs - Vth when operating in the variable resistance region, wherein Vgs is electric The voltage drop between the gate terminal and the source terminal of the crystal Q2, Vds is the source voltage drop of the transistor Q2, and Vth is the threshold voltage of the transistor Q2. Therefore, the LED feedback control circuit 15 detects the output voltage of the LED lamp strings LB1 LB LBn through the diodes D11 D Din, and controls the PWM controller U11 to increase the transistor according to the lowest of the detected output terminal voltages. The switching duty cycle of Q1 is to increase the input voltage Vin of the string, so that the voltage drop falling in all the constant current source circuits 141 to 14n is in a reasonable state and can be normally operated to perform constant current control on the LED strings LB1 to LBn. In addition, if the number of LED short circuits in the LED string is too large, the voltage drop of the germanium source falling into the transistor Q2 in the constant current source circuit may be high to increase the power consumption or even burn the transistor Q2. Therefore, the LED short circuit protection circuit 16 detects the output of the LED lamp strings LB 1 LB LBn through the diodes D21 DD2 to D2n and turns off the PWM when the highest of the detected output voltages is greater than the protection point voltage. The controller un causes the boost converter circuit 13 to no longer perform boost conversion to protect internal components such as transistors of the constant current source circuit from burning. The motherboard microcontroller can output the switching signal 〇n/Off and the dimming signal Dim. Among them, the switch signal 〇n/〇ff is used to turn off the pwM controller U11 in the standby mode to make it more energy-saving in the standby mode. The dimming signal Dim is used to control the working and non-operating states of the constant current source circuits 141 to 14n through the dimming control circuit 17, thereby controlling the working and non-operating states of the LED light strings LB1 LB LB to control the LED light strings U1 LB LBn to be issued. The average brightness of the light, which is the burst mode dimming. 10120751^^51 A0101 Page 5/Total 23 page 1012024557-0 [0007] The conventional LED driving circuit 1 uses the bus bar voltage Vbus to first pass through the boosting of the main power circuit 11 and is boosted by the boost converter circuit 13 to generate material. The input voltage Vin is provided to provide the working electric house of the coffee light string U1~Un, so that the power conversion efficiency after two energy conversions will be reduced. Secondly, the constant current source circuits 141 to 14n usually adopt a shunt regulator U21 such as AZ432, and the reference terminal _ is stabilized at 1 25V. When the working power of the LED string is large, it is lightly connected between the reference peach and the ground. The resistor Μ will have a large power consumption, which is equivalent to reducing the power conversion efficiency. [New Content] [0008] The purpose of this creation is to propose an LED driver circuit that optimizes the existing LED driver circuit to achieve lower design cost and improved power conversion efficiency. In order to achieve the above object or other objects, the present invention proposes an LED driving circuit comprising a main power supply circuit, an LED feedback control circuit, n constant current source circuits and a dimming control circuit, wherein n is a positive integer. The main power circuit includes a main power converter and an output anti-lock control circuit. The main power converter receives the bus voltage generated by the rectification, power factor correction and filtering of the AC mains and accordingly generates a mains voltage output from the output of the main power circuit to the input of the n LED strings. The output feedback control circuit includes a first sampling resistor and a second sampling resistor. The first sampling resistor is coupled between the output end of the main power circuit and the feedback end, and the second sampling resistor is coupled to the feedback end and the ground. The output feedback control circuit controls the main power converter to adjust the main power voltage according to the feedback terminal voltage. The LED feedback control circuit is coupled to the wheel-out terminal of the LED lamp, and the switch and the third sampling resistor are coupled in series with the feedback. Between the terminal and the ground, when detecting any LED string 10120751^Single number A0101 Page 6/Total 23 page 1012024557-0 M438012 When the output terminal voltage is less than the compensation point voltage, the control switch is turned on, otherwise the control switch is turned off. . Each constant current source circuit includes a transistor, an operational amplifier and a resistor. The transistor and the resistor are coupled in series between the output end of the corresponding LED string and the ground, and the operational amplifier detects the voltage across the resistor and The reference voltage is compared and the transistor is controlled to make the operating current of the corresponding LED string constant. The dimming control circuit is coupled to the constant current source circuit, receives the dimming signal, and accordingly controls the constant current source circuit to operate and not in operation to implement burst mode dimming.

[0010] In an embodiment of the present invention, the dimming control circuit is further coupled to the LED feedback control circuit, and controls whether the LED feedback control circuit operates according to the dimming signal. [0011] In an embodiment of the present invention, the LED driving circuit further includes a reference voltage source circuit. A reference voltage source circuit is coupled to the constant current source circuit to generate a reference voltage of less than 1.25 volts. In an embodiment of the present invention, the LED driving circuit further includes an LED short circuit protection circuit. The LED short circuit protection circuit is coupled to the output end of the LED light string. When the LED light string is working normally, the protection signal is output when the output voltage of any LED light string is detected to be greater than the protection point voltage, and vice versa. The protection signal, wherein the protection signal causes the dimming control circuit to control the constant current source circuit to stop working by the dimming signal. [0012] In an embodiment of the present invention, the LED driving circuit is suitable for a liquid crystal display product such as a liquid crystal display or a liquid crystal television. LCD products include motherboard microcontrollers. The motherboard micro controller is coupled to the dimming control circuit and the LED short circuit protection circuit, and outputs a dimming signal and causes the dimming control circuit to control the constant current source circuit to stop working when the protection signal is received. 10 Lan 51# Single No. A0101 Page 7 / Total 23 1012024557-0 M438012 In an embodiment of the present invention, the LED driving circuit further includes a standby power supply circuit. The standby power circuit receives the bus voltage and generates a standby power supply voltage to the motherboard microcontroller.

The LED driving circuit of the present invention directly outputs the main power voltage generated by the voltage conversion of the mains power circuit to the input end of the LED string to provide the working voltage required for the LED string, so that only the energy is passed. The conversion power conversion efficiency will be improved; secondly, the constant current source circuit uses an operational amplifier to receive the lower reference voltage generated by the reference voltage source circuit to compare with the voltage corresponding to the LED lamp series current, thereby reducing the constant Power consumption of the stream source circuit. In addition, the 1^]) drive circuit of this creation also uses the LED feedback control circuit to adjust the main power supply voltage accordingly, so that the voltage drop falling in the constant current source circuit is in a reasonable state and can work normally to the LED string. Flow control; and the LED short circuit protection circuit is used when the number of LED shorts in the ud string is too large, causing the output voltage to be too large.

The feedback control circuit causes the main power circuit to no longer perform voltage conversion to protect the internal components from burning. The above and other objects, features and advantages of the present invention will become more apparent and understood. 4 is a block diagram of an LED driving circuit suitable for a large-sized liquid crystal display product according to an embodiment of the present invention, and FIG. 4 is a circuit diagram of the LED driving circuit shown in FIG. Please also refer to Figure 3 and Figure 4. Large-size LCD display usually needs to use high-power LED light source. This high-power LED light source is 10120751$ soap number A01 (n page 8 / total 23 pages 1012024557-0 M438012 often by LED The LED strings LB1 LBLBn are configured, and each _LED light string comprises a plurality of LEDs coupled in series, wherein n is a positive integer. When 11 is greater than 丨, the LED light strings LB1 LBLBn are driven in parallel. LED driving circuit 2 for driving LED light strings LB1 LBLBn, including main power circuit 21, standby power circuit 22, reference voltage source circuit 23, n constant current source circuits 241 〜 24n, LED feedback control circuit 25 'LED short circuit protection circuit 26 And the dimming control circuit 27. [0017] The LED driving circuit 2 receives the stable DC bus voltage Vbus generated by the rectification, power factor correction and filtering of the AC mains, which is generally about 400 V. The bus bar voltage Vbus passes through the main power circuit. After the step-down of 21, the main power supply voltages Vml and Vm2' are respectively 86V and 12V. Among them, the main power supply voltage Vml is used for direct output to the input terminals of the LED light strings LB1 LBLBn as the light string input voltage, so that only once The power conversion efficiency of the quantity conversion will be improved. The main power supply voltage Vm2 is used to provide the required power supply for the liquid crystal display, such as the audio circuit and the panel drive circuit. The bus voltage Vbus is also generated by the step-down of the standby power supply circuit 22. The standby power supply voltage Vsb, for example, 5V, is used to provide power required for components in the liquid crystal display product, such as the motherboard micro-controller H, which are still required to be operated in the standby mode, and provides the reference voltage source circuit 23 and the dimming control circuit 27 Power Supply Required [0018] The main power supply circuit 21 includes a main power converter 211, an output filter circuit 212, and an output anti-river control circuit 213. The main power converter 211 is, for example, a buck converter for receiving AC mains. After rectification, power factor correction and later generation of bus voltage Vbus, and according to the output of the main f source voltage Vml from the output of the main power circuit 21 to 10120751# single number A0101 page 9 / 23 pages 1012024557-0 M438012 LED lamp string LB 1·~ LBn input terminal. Output filter circuit 212 includes capacitors C1 and C2 and inductor L1 for reducing mains output of main power converter 211 The voltage Vml is chopped. The output feedback control circuit 213 includes a first sampling resistor Rfl, a second sampling resistor Rf2, resistors ri and R2, a capacitor C3, a shunt regulator U22, an optocoupler U3, and a PWM controller U12. The first sampling resistor Rf1 is coupled between the output end of the main power circuit 21 and the feedback terminal FB, and the second sampling resistor Rf2 is connected between the feedback terminal FB and the ground. The output feedback control circuit 213 detects the main power supply voltage ¥1111 through the first sampling resistor Rfl and the second sampling resistor Rf2, and the feedback terminal FB voltage corresponds to the detected main power supply voltage Vml, and the feedback terminal FB % voltage passes. The shunt regulator U22 amplifies the error and then transmits it to the PWM controller U12 via the optical coupling SU3 to control the switching duty cycle in the main power converter 211 to adjust the main power supply voltage Vml to stabilize. When the shunt regulator U22 uses the TL431, it has a reference voltage source of 2. 5V, and the reference terminal R voltage will be stable at 2. 5V, so the main power supply voltage Vml = 2. 5Vx (Rfl+Rf2)/Rf2. [0019] The reference voltage source circuit 23 includes a transistor Q1, a shunt regulator U23, φ resistors R3 R R5 and a capacitor C4 for receiving power supply of the standby power supply voltage Vsb and accordingly generating a precise reference voltage Vrl. When the shunt regulator U23 uses TL431, 'Vrl=2.5 Vx(R4 + R5)/R5. The reference voltage source circuit 23 further includes resistors R6 and R7 for further generating a reference voltage Vr of less than 1.25 V, Vr = VrlxR7 / (R6 + R7). [0020] The constant current source circuits 241 〜 24 η are respectively coupled to the output ends of the LED light strings LB1 LB LBn for controlling the currents of the LED light strings LB1 LB LBn to be constant and equal in size. Each constant current source circuit 24i includes a transistor Mi, an operation 10120751# single number A0101 page 10 / 23 pages 1012024557-0 M438012

[0021] The amplifier OPi and the resistor Rsi, wherein i is any positive integer from 1 to η. The transistor Mi has a first end, a second end and a control end. In this example, the transistor Mi is an N-channel field effect transistor, and the first end, the second end and the control end are respectively a 汲 extreme, a source terminal and The gate is extreme. The 汲 terminal and the source terminal of the transistor Mi are respectively coupled to the output end of the LED lamp string LBi and the first end of the resistor Rsi, and the second end of the resistor Rsi is coupled to the ground, so the transistor Mi and the resistor Rsi The series is coupled between the output end of the corresponding LED string LBi and the ground. The operational amplifier OPi has a positive power terminal, a negative power terminal, a positive input terminal, a negative input terminal and an output terminal, and the positive power terminal receives the power supply of the internal power supply voltage Vcc and the negative power terminal is coupled to the ground, and the positive input terminal receives the reference voltage source. The circuit 23 generates a reference voltage Vr of less than 1.2 5V and the negative input terminal is coupled to the first end of the resistor Rs i to detect the voltage across the resistor Rs i , which corresponds to the operating current of the LED string LBi. Therefore, the operational amplifier OPi compares the voltage across the resistor Rsi with the reference voltage Vr to output a signal from its output terminal to the gate terminal of the transistor Mi to adjust the source voltage drop, so that the operating current of the LED string LBi is constant and its The value is Ilbi=Vr/Rsi. When Vr = 0.3V and Ilbi = 150mA, the resistance of the resistor Rsi is 2Ω. The constant current source circuits 241 to 24n can reduce the power consumption of the resistors Rsi to Rsn connected between the transistor and the ground by using a lower reference voltage Vr, which is equivalent to improving the power conversion efficiency. The LED feedback control circuit 25 includes a transistor Q2 as a switch, a third sampling resistor Rf3, an operational amplifier OP, resistors R8 to R14, and a capacitor C5. The transistor Q2 has a first end, a second end, and a control end, the The first end and the second end are respectively coupled to the first end of the feedback terminal FB and the third sampling resistor Rf 3 , and the second end of the third sampling resistor Rf 3 is coupled to the ground, so the transistor Q2 as the switch The third sampling resistor Ri3 is coupled in series with the feedback 10120751, the order number A0101, the 11th page, the 23rd page, the 1012024557-0, the M438012 terminal FB and the ground. The positive power terminal of the operational amplifier OP receives the power supply of the internal power supply voltage Vcc and the negative power supply terminal is coupled to the ground, the positive input terminal receives the compensation point voltage and the negative input terminal is coupled to the connection terminal FBI to pass the diodes di 1 to Dl η The output terminals of the LED lamp strings LB1 to LBn are respectively connected to the output terminals of the LED lamp strings LB1 to LBn. Wherein, the value of the compensation point voltage is VR9x (R12 + R13 + R14) / (Rll + R12 + R13 + R14), and the voltage across the resistor R9 is VR9 = Vrlx [R9 / / (Rll + R12 + R13 + R14) ]/[R8 + R9/V(R11+R12+R13+R14)]. [0022]

The operational amplifier OP compares the lowest of the output voltages of the LED strings LB1 〜 'LBn detected by the negative input terminal with the compensation point voltage received by the positive input terminal, so as to output a signal from the output terminal to the transistor Q2. The control terminal controls its conduction or disconnection. When the lowest of the output voltages of the LED strings LB1 LBLBn is less than the compensation point voltage, the output voltage of any LED string is detected to be less than the compensation point voltage. When it is indicated that the voltage drop of the diode in the constant current source circuit is low, there will be a normal operation in the constant current region to become working in the variable resistance region and it is impossible to make a constant current to the LED string. The risk of control, at this time, the operational amplifier OP controls the transistor Q2 to be turned on, so that the second sampling resistor Rf 2 in the output switching control circuit 213 is equivalent to being coupled in parallel with a resistor R, which is R = Rds2 + Rf3 , where Rds2 is the on-resistance value of the 汲 terminal and the source terminal of the transistor Q2, so the main power supply voltage 乂1111=2.5¥\([^1+1^2//1〇/(1^2//1 〇, the main power supply voltage Vml rises, causing the voltage drop to fall in all the constant current source circuits 241 to 24n It is in a reasonable state and can work normally to perform constant current control on the LED light strings LB1~LBn. Conversely, when it is detected that the output voltages of the LED light strings LB1 LB LBn are greater than the compensation point voltage, it means that the landing is in all 10120751 production orders. The voltage drop in the constant current source circuits 241 to 24n is in a reasonable state and can be normal. 101 0101 Page 12 / Total 23 1012024557-0 [0023] M-438012

[0024] 10120751^^^ The operation is to perform constant current control on the LED lamp strings LB1 to LBn, and the operational amplifier OP controls the transistor Q2 to be turned off. The LED short circuit protection circuit 26 includes Zener diodes ZD1 and ZD2, resistors R15*R16 and capacitor C6. The cathode end of the Zener diode ZD1 is braided to the connection terminal DET1 to pass the diode! 21~D2n are respectively coupled to the output ends of the LED light strings LB1 LBLBn to measure the output voltage of the LED string lb 1~ LBn. The resistors Rl5 and R16 are coupled in series to the anode end of the Zener diode ZD1. Between the ground and the ground. Both ends of the capacitor C6 are respectively coupled to both ends of the resistor R16. The capacitor C6 is used to pulsate high frequency noise. The cathode end and the anode end of the Zener diode ZD2 are respectively coupled to the two ends of the resistor R16, and the cathode end of the Zener diode ZD2 is also coupled to the protection end det to be coupled to the main board micro controller. The nano-diode ZD2 is used as a voltage button for the protection terminal DET, and the protection terminal is blocked when the dimming signal Dini is at a low level and the transistors M1 to Μη in the constant current source circuits 24]1 to 24n are turned off. The DET voltage will not exceed the maximum withstand voltage of the corresponding pin of the motherboard microcontroller. Wherein, the value of the protection point voltage is (Vdetl-Vzl)xRl6/〇U5+R16), Vzl is the breakdown voltage of the Zener diode ZD1, and Vdetl is the voltage of the connection terminal DET1 and its value is the LED light string LB1~LBn The highest of the output voltages is subtracted from the diode forward voltage that it is coupled to. When it is detected that the highest of the round-trip voltages of the LED light strings LB1 LBLBn is greater than the protection point voltage, that is, when the output voltage of any LED light string is detected to be greater than the protection point voltage, it indicates that the LED light string is in the LED string. The number of LED short circuits is too large, causing the voltage drop of the transistor in the corresponding constant current source circuit to be high, increasing the power consumption or the risk of burning the transistor. At this time, the protection terminal DET voltage is at a high level. Equivalent to outputting the protection signal to the motherboard microcontroller. A0101 Page 13 of 23 1012024557-0 [0025] Conversely 'When the voltage at the output of the LED string LB1~LBn is less than the protection point voltage', it means that the number of LED shorts in all L strings LB1~LBn is In advance. Within the range of values, not too much power consumption or the risk of burning the transistor. At this point, the protection terminal DETM is at a low level, and the protection signal is not output to the motherboard microcontroller. The field control circuit 27 includes transistors Q3 and Q4 and resistors R17 R R19 for receiving the dimming signal Dim and controlling the constant current source circuits 241 〜 24 η to operate in a state to achieve burst mode modulation. Light. When the dimming number Dlm is at a high level, the transistors Q3 and Q4 are both turned on, and the standby power supply clock Vsb received by the emitter end of the transistor can be transmitted to the collector terminal of the transistor 而 to output the internal supply voltage Vcc, Vcc = Vsb_Vec4, where "Vec4 is the voltage drop between the emitter terminal and the collector terminal when the transistor Q4 is turned on, so the internal supply voltage Vcc is supplied to the constant current source circuits 241~24n and the LED feedback control circuit 25 to operate, thereby enabling Led light string LB1 ~ ϋ U.

Conversely, when the dimming signal Dim is at a low level, the transistor (10) and the "average gate, the standby power supply voltage Vsb received by the emitter terminal of the transistor Q4 is not, ^ r^· to the collector terminal of the transistor Q4 without Then, the internal power supply voltage Vc is output, so that the constant current source circuits 241 to 24n and the LED feedback control circuit 25 no longer have power supply.

The operation is stopped, and the LED light strings LB1 to LBn are stopped. Therefore, the ratio of the high level of the dimming signal Dim to the low level, g. Refer to J "1Λ. The ratio of the working and non-working time of the constant current source and circuit 241~24η, and then control the ratio of the working time of the LED light string LB1~LBn to no operation, so as to control the LED light string LB1~LBn to emit light. The average brightness, which is the six-shot mode dimming. [0026] Motherboard Microcontroller can output switching signal On/Off and dimming signal ^^^ (8) Rattan single number surface 1 Page 14 / Total 23 1012024557-0 M4J8012

Among them, the switch k No. On/Off is used to turn off the 丨(4) controller U12 in the standby mode to make it more energy-saving in the standby mode. The dimming signal Dim is used to control the operation and non-operation states of the constant current source circuits 241 to 24n by the dimming control circuit 27 to realize burst mode dimming. Moreover, the motherboard micro-control benefit can be set to determine whether the protection terminal DET is at a high level or receives a protection signal only when the dimming signal Dim is at a high level (ie, when the LED light strings LB1 LB LBn are working normally), once the protection end The DET is at a high level or receives a protection signal. 'The motherboard microcontroller immediately causes the dimming control circuit 27 to control the constant current source circuits 241 to 24n and the LED feedback control circuit 25 to stop working by the dimming signal Dim', thereby causing the LED string to be turned on. LB1~LBn stop working to protect internal components from burning. [0027] Although the present invention has been disclosed in the above preferred embodiments, it is not intended to limit the present invention, and it is possible to make some changes and refinements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of this creation is subject to the definition of the scope of the patent application attached. BRIEF DESCRIPTION OF THE DRAWINGS [0028] FIG. 1 is a block diagram of an LED driving circuit commonly used in a large-sized liquid crystal display product. [0031] FIG. 2 is a circuit diagram of a constant current source circuit of the conventional three-terminal adjustable shunt regulator shown in FIG. Fig. 3 is a block diagram of an LED driving circuit suitable for a large-sized liquid crystal display product according to an embodiment of the present invention. 4 is a circuit diagram of the LED flip circuit shown in FIG. [Description of main component symbols] 1〇面单单编号1 1 page 15/23 pages 1012024557-0 M438012 [0032] 1 : LED driver circuit 11: main power circuit [0033] 12: standby power circuit 13: boost Conversion circuit [0034] 141 to 14n: constant current source circuit 15: LED feedback control circuit [0035] 1 6 : LED short circuit protection circuit 17: dimming control circuit [0036] 2 : LED drive circuit 21: main power supply circuit [0037 211: main power converter 21 2 : output filter circuit [0038] 213 : output feedback control circuit 22 : standby power supply circuit [0039] 23 : reference voltage source circuit 241 to 24n : constant current source circuit [0040] 25 : LED Feedback control circuit 26: LED short circuit protection circuit [0041] 27: Dimming control circuit C1~C6: Capacitor [0042} Dl, D11~Din: Diode D21~D2n: Diode [0043] L1: Inductor LB1 ~LBn : LED light string [0044] Ml~Mn, Q1~Q4: transistor 0P: operational amplifier [0045] ΟΡ1~ΟΡn: operational amplifier R1~R19: resistor [0046] Rfl: first sampling resistor Rf2: Second sampling resistor [0047] Rf3: third sampling resistor Rsl~Rsn: resistor [0048 UU, U12: PWM controller U21~U23: shunt regulator [0049] 113: optocoupler ZD1, ZD2: Zener diode [0050] A: anode terminal of shunt regulator K: shunt regulator Cathode terminal [0051] R: Reference terminal DET1, FBI of the shunt regulator: connection terminal

10120751^^^^ A〇101 ? 16 I / * 23 1 1012024557-0 M438012 [0052] DET: protection terminal FB: feedback terminal [0053] Vbus: bus voltage Vml, Vm2: main power supply voltage [0054] Vsb : Standby power supply voltage Vin: string input voltage [0055] Vr, Vrl: reference voltage Vcc: internal supply voltage [0056] Ilbl~Ilbn: current On/Off: switching signal [0057] Dim: dimming signal

10120751#单号 A_ Page 17 of 23 1012024557-0

Claims (1)

M438012 VI. Application Patent Range: 1. A light-emitting diode driving circuit, comprising: A main power supply circuit includes a main power converter and an output feedback control circuit, and the main power converter receives a bus voltage generated by rectification, power factor correction and filtering of the AC mains and generates a main power voltage accordingly An output end of the main power circuit is output to an input end of the n LED strings, the output feedback control circuit includes a first sampling resistor and a second sampling resistor, the first sampling resistor is coupled to Between the output end of the main power circuit and a feedback terminal, the second sampling resistor is coupled between the feedback terminal and the ground, and the output feedback control circuit controls the main power converter to adjust the main according to the feedback terminal voltage. a power supply voltage, where η is a positive integer; a light-emitting diode feedback control circuit coupled to the output end of the light-emitting diode string, including a switch and a third sampling resistor coupled in series to the feedback end Between the ground and the ground, the switch is controlled to be turned on when detecting that the output voltage of any of the LED strings is less than a compensation point voltage, and vice versa. η constant current source circuits, wherein each constant current source circuit comprises a transistor, an operational amplifier and a resistor, and the transistor is coupled in series with the resistor at an output end of a corresponding LED string Between the ground and the ground, the operational amplifier detects the voltage across the resistor and compares it with a reference voltage and controls the transistor to make the operating current of the corresponding LED string constant; a dimming control circuit, And coupled to the constant current source circuits, receive a dimming signal and accordingly control the working and non-operating states of the constant current source circuits to implement burst mode dimming. 2. The LED driving circuit of claim 1, wherein the dimming control circuit is further coupled to the LED feedback control circuit, 10120751#单单Α〇101第18页/ a total of 23 pages 1012024557-0 M438012 control the light-emitting diode feedback control circuit according to the dimming signal operation or not. The light-emitting diode driving circuit according to claim 1, further comprising a reference voltage And the reference voltage source circuit is coupled to the constant current source circuit to generate the reference voltage of less than 1.25 volts. 4. The LED driving circuit of claim 1, further comprising a light-emitting diode short-circuit protection circuit coupled to the light-emitting diode string At the output end, when the LED strings are normally operated, when a voltage of the output terminal of any of the LED strings is detected to be greater than a protection point voltage, a signal is output, and vice versa. The protection signal, through the dimming signal, causes the dimming control circuit to control the constant current source circuits to stop working. 5. The LED driving circuit of claim 4, which is suitable for a liquid crystal display product, the liquid crystal display product comprising a motherboard micro controller coupled to the dimming control circuit And the light-emitting diode short-circuit protection circuit outputs the dimming signal and, when receiving the protection signal, causes the dimming control circuit to control the constant current source circuits to stop working by the dimming signal. 6. The LED driving circuit of claim 5, further comprising a standby power circuit, the standby power circuit receiving the bus voltage and generating a standby power voltage to supply the motherboard micro controller . 7. The LED driving circuit of claim 5, wherein the liquid crystal display product comprises a liquid crystal display or a liquid crystal television. 1()12()751f单单A0101 Page 19 of 23 1012024557-0