CN102711321B - Light emitting diode driving circuit - Google Patents
Light emitting diode driving circuit Download PDFInfo
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- CN102711321B CN102711321B CN201210136261.7A CN201210136261A CN102711321B CN 102711321 B CN102711321 B CN 102711321B CN 201210136261 A CN201210136261 A CN 201210136261A CN 102711321 B CN102711321 B CN 102711321B
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Abstract
The invention relates to a light emitting diode driving circuit which comprises a main power source circuit, a reference voltage source circuit, constant-current source circuits, an LED feedback control circuit, an LED short-circuit protecting circuit and a light dimming control circuit. The main power source circuit receives a bus voltage and generates main power source voltage to directly supply for working voltage required by LED lamp strings according to the bus voltage, the constant-current source circuits receive lower reference voltage generated by the reference voltage source circuit by an operational amplifier so as to compare with voltage corresponding to the working current of the LED lamp strings, and power source conversion efficiency can be improved. The LED feedback control circuit adjusts the main power source voltage correspondingly so as to guarantee reasonable voltage drop in the constant-current source circuits and realize constant-current control on the LED lamp strings. The LED short-circuit protecting circuit can control inoperation of all the constant-current source circuits in overhigh voltage of an output end when LEDs in the LED lamp strings are in short circuit, so that transistors inside constant-current sources can be protected from being damaged by overheat.
Description
Technical field
The invention relates to a kind of light-emitting diode (Light-Emitting Diode, LED) drive circuit, and particularly relevant for a kind of LED drive circuit that is applicable to high-powered LED lamp source.
Background technology
Fig. 1 is a kind of existing calcspar that large scale liquid crystal shows the LED drive circuit of product that is often applied in.Refer to Fig. 1, large scale liquid crystal shows that product need to be used high-powered LED lamp source conventionally, and this high-powered LED lamp source is consisted of LED lamp string LB1～LBn conventionally, and each LED lamp string comprises the LED of a plurality of coupled in series, and wherein n is positive integer.When n is greater than 1, these LED lamp strings LB1～LBn adopts parallel way to drive.LED drive circuit 1 is for driving LED lamp string LB1～LBn, and it comprises main power circuit 11, standby power circuit 12, (boost) change-over circuit 13 that boosts, constant-current source circuit 141～14n, LED feedback control circuit 15, LED short-circuit protection circuit 16 and adjusting control circuit 17.
LED drive circuit 1 receives the stable DC bus voltage Vbus that electric main produces after over commutation, power factor correction (Power Factor Corrector, PFC) and filtering, is generally about 400 volts (volt, V).Bus voltage Vbus produces main power voltage Vm1 and Vm2 after the step-down of main power circuit 11, for example, be respectively 24V and 12V.Wherein, main power voltage Vm1 is for again through producing the fluorescent tube input voltage vin that is slightly larger than the required operating voltage of LED lamp string after the boosting of voltage up converting circuit 13, for example: during work, LED lamp tube ends voltage is 85V, after boosting, to offer lamp string input voltage be 86V to voltage up converting circuit, to export the input of LED lamp string LB1～LBn to.Main power voltage Vm2 is for providing liquid crystal display product inner as required power supplys such as message circuit (Audio Circuit) and liquid crystal panel (Panel) drive circuits.Bus voltage Vbus separately produces standby power voltage Vsb after the step-down of standby power circuit 12, be for example: 5V, be used for providing that liquid crystal display product is inner under standby mode, still needs the required power supply of assembly of work as mainboard micro controller (Micro Control Unit, MCU) etc.
Voltage up converting circuit 13 comprises boost converter, output filter circuit and output feedback control circuit.Wherein, boost converter comprises as the inductor L1 of energy storage component and transistor Q1 and diode D1 as switch module, for the lower direct current of input is converted to the required relatively high work input voltage of each LED lamp string.Output filter circuit comprises capacitor C1, for reducing the output voltage ripple of boost converter.Output feedback control circuit comprises pulse-width modulation (Pulse-Width Modulation, PWM) controller U11, for controlling the switch responsibility cycle of transistor Q1 with the output voltage (being lamp string input voltage vin in this example) of adjustment boost converter according to the output voltage of LED feedback control circuit 15.Constant-current source circuit 141～14n is coupled to respectively the output of LED lamp string LB1～LBn, for controlling LED lamp string LB1～LBn current constant and equal and opposite in direction when working.Refer to Fig. 2, it is the circuit diagram of the constant-current source circuit of the adjustable shunt regulator of existing normal employing three end.Take constant-current source circuit 141 as example, and it comprises transistor Q2, resistor R1～R3 and the shunt regulator U21 with anode tap A, cathode terminal K and reference edge R.Adopt as shunt regulator U21 as: during AZ432, its inside has the reference voltage source of a 1.25V, and reference edge R voltage will be stabilized in 1.25V, and making constant and its value of the operating current Ilb1 of LED lamp string LB1 is Ilb1=1.25V/R1.
Please again referring to Fig. 1 and coordinate Fig. 2, if the output end voltage of LED lamp string is too low, dropping to the drain electrode end of transistor Q2 in constant-current source circuit and the pressure drop between source terminal (calling drain-source extreme pressure in the following text falls) can be on the low side and become and be operated in variable resistor district and cannot do constant current to LED lamp string and control from being originally normally operated in constant current district, wherein, Vgs>Vth and Vds>Vgs-Vth while working in constant current district, Vgs>Vth and Vds<Vgs-Vth while working in variable resistor district, wherein, Vgs is the gate terminal of transistor Q2 and the pressure drop between source terminal, Vds is that the drain-source extreme pressure of transistor Q2 falls, Vth is the cut-in voltage (threshold voltage) of transistor Q2.Therefore, LED feedback control circuit 15 is by the output end voltage of diode D11～D1n detecting LED lamp string LB1～LBn, and control switch responsibility cycle that whether PWM controller U11 will strengthen transistor Q1 to improve lamp string input voltage vin according to the lowest in detected output end voltage, make to drop to pressure drop in all constant-current source circuit 141～14n and all in rational state, can normally work and LED lamp string LB1～LBn is done to constant current control.In addition, if the LED short circuit number in LED lamp string is too many, the drain-source extreme pressure that drops to transistor Q2 in constant-current source circuit falls can be higher and increase power consumption or even because electric transistor Q2 is because of the overheated transistor Q2 that damages.Therefore; LED short-circuit protection circuit 16 is by the output end voltage of diode D21～D2n detecting LED lamp string LB1～LBn; and soprano is greater than while protecting point voltage in detected output end voltage; close PWM controller U1; make voltage up converting circuit 13 no longer do boost conversion, to protect the electronic components such as transistor of constant-current source circuit not destroyed.
The exportable switching signal of mainboard micro controller (On/Off) and dim signal (Dim).Wherein, switching signal (On/Off), for close PWM controller U1 under standby mode, makes it energy saving more under standby mode.Dim signal (Dim) is for controlling constant-current source circuit 141～14n work and off position by adjusting control circuit 17, and then control LED lamp string LB1～LBn and work and off position, to reach, control the mean flow rate that LED lamp string LB1～LBn sends light, this is burst mode (burst mode) light modulation.
Existing LED drive circuit 1 adopts bus voltage Vbus first through the step-down of main power circuit 11, to produce lamp string input voltage vin so that the required operating voltage of LED lamp string LB1～LBn to be provided again through after the boosting of voltage up converting circuit 13, and the power supply conversion efficiency through twice power conversion will reduce like this.Secondly, constant-current source circuit 141～14n conventionally adopts as the shunt regulator U21 of AZ432, and its reference edge R voltage stabilization is at 1.25V, when the operating current of LED lamp string is larger, the resistor R1 being coupled between reference edge R and ground will have larger power consumption, is equivalent to reduce power supply conversion efficiency.
Summary of the invention
Object of the present invention is proposing a kind of LED drive circuit, and existing LED drive circuit is further improved to reach lower design cost and raising power supply conversion efficiency.
For achieving the above object or other object, the present invention proposes a kind of LED drive circuit, comprises main power circuit, LED feedback control circuit, a n constant-current source circuit and adjusting control circuit, and wherein n is positive integer.Main power circuit comprises main power source transducer and output feedback control circuit.Also produce according to this main power voltage exports the input of n LED lamp string to the bus voltage that main power source transducer reception electric main produces after rectification, power factor correction and filtering from the output of main power circuit.Output feedback control circuit comprises the first sampling resistor and the second sampling resistor, the first sampling resistor is coupled between the output and feedback end of main power circuit, the second sampling resistor is coupled between feedback end and ground, and output feedback control circuit is adjusted main power voltage according to feedback end voltage control main power source transducer.LED feedback control circuit is coupled to the output of described LED lamp string, comprise that switch and the 3rd sampling resistor coupled in series are between feedback end and ground, when the output end voltage that detects arbitrary LED lamp string is less than compensation point voltage, control switch conduction, otherwise control switch disconnects.Each constant-current source circuit comprises transistor, operational amplifier and resistor, transistor AND gate resistor in series is coupled between the output and ground of corresponding LED lamp string, and the cross-pressure of operational amplifier detecting resistor and relatively and according to this control transistor with reference voltage and make the operating current of corresponding LED lamp string constant.Adjusting control circuit is coupled to described constant-current source circuit, receives dim signal and also controls according to this described constant-current source circuit work and off position to realize burst mode light dimming.
In an embodiment of the present invention, adjusting control circuit is also coupled to LED feedback control circuit, according to dim signal, whether controls the work of LED feedback control circuit.
In an embodiment of the present invention, LED drive circuit also comprises reference voltage source circuit.Reference voltage source circuit is coupled to described constant-current source circuit, produces the reference voltage that is less than 1.25 volts.
In an embodiment of the present invention, LED drive circuit also comprises LED short-circuit protection circuit.LED short-circuit protection circuit is coupled to the output of described LED lamp string; when LED lamp string is worked; when detecting the output end voltage of arbitrary LED lamp string, be greater than protection output protection signal during point voltage; otherwise output protection signal not; wherein, guard signal makes adjusting control circuit control described constant-current source circuit by dim signal to quit work.
In an embodiment of the present invention, LED drive circuit is applicable to liquid crystal display product, such as liquid crystal display or LCD TV etc.Liquid crystal display product comprises mainboard micro controller.Mainboard micro controller is coupled to adjusting control circuit and LED short-circuit protection circuit, exports dim signal and by dim signal, make adjusting control circuit control described constant-current source circuit when receiving guard signal to quit work.
In an embodiment of the present invention, LED drive circuit also comprises standby power circuit.Standby power circuit receives bus voltage and produces according to this standby power power voltage supply to mainboard micro controller.
The input that the main power voltage that LED drive circuit of the present invention produces after the voltage transitions of main power circuit because of employing bus voltage directly exports LED lamp string to is to provide LED lamp string required operating voltage, and so only the power supply conversion efficiency through primary energy conversion will improve; Secondly, because constant-current source circuit adopts operational amplifier to receive the lower reference voltage being produced by reference voltage source circuit, with the voltage corresponding with LED lamp string operating current, compare, thereby can reduce the power consumption of constant-current source circuit.In addition, LED drive circuit of the present invention also adopts LED feedback control circuit to adjust accordingly main power voltage, makes to drop to pressure drop in constant-current source circuit and all in rational state, can normally work and LED lamp string is done to constant current control; And adopt LED short-circuit protection circuit to detect each LED lamp string output end voltage whether to have the protection point that exceeds the estimates fixed; while surpassing the protection point presetting when LED short-circuit protection circuit detects a certain LED lamp string output end voltage in work; the dim signal output port of mainboard micro controller will be exported one and continue low level signal to adjusting control circuit; use the transistor of constant-current source circuit inside to be closed, to protect the electric transistor of constant-current source circuit inside not because of overheated and destroyed.
For above and other objects of the present invention, feature and advantage can be become apparent, preferred embodiment cited below particularly, and coordinate appended graphicly, be described in detail below.
Accompanying drawing explanation
Fig. 1 is a kind of existing calcspar that large scale liquid crystal shows the LED drive circuit of product that is often applied in.
Fig. 2 is the circuit diagram of the constant-current source circuit of the adjustable shunt regulator of existing normal employing three end shown in Fig. 1.
Fig. 3 shows the calcspar of the LED drive circuit of product for being applicable to according to an embodiment of the invention large scale liquid crystal.
Fig. 4 is the circuit diagram of LED drive circuit shown in Fig. 3.
[primary clustering symbol description]
1:LED drive circuit 11: main power circuit
12: standby power circuit 13: voltage up converting circuit
141～14n: constant-current source circuit 15:LED feedback control circuit
16:LED short-circuit protection circuit 17: adjusting control circuit
2:LED drive circuit 21: main power circuit
211: main power source transducer 212: output filter circuit
213: output feedback control circuit 22: standby power circuit
23: reference voltage source circuit 241～24n: constant-current source circuit
25:LED feedback control circuit 26:LED short-circuit protection circuit
27: adjusting control circuit C1～C6: capacitor
D1, D11～D1n: diode D21～D2n: diode
L1: inductor LB1～LBn:LED lamp string
M1～Mn, Q1～Q4: transistor OP: operational amplifier
OP1～OPn: operational amplifier R1～R19: resistor
Rf1: the first sampling resistor Rf2: the second sampling resistor
Rf3: the 3rd sampling resistor Rs1～Rsn: resistor
U11, U12:PWM controller U21～U23: shunt regulator
U3: optical coupler ZD1, ZD2: Zener diode
A: the anode tap K of shunt regulator: the cathode terminal of shunt regulator
R: reference edge DET1, the FB1 of shunt regulator: link
DET: protection end FB: feedback end
Vbus: bus voltage Vm1, Vm2: main power voltage
Vsb: standby power voltage Vin: lamp string input voltage
Vr, Vr1: reference voltage Vcc: internal supply voltage
Ilb1: electric current On/Off: switching signal
Dim: dim signal.
Embodiment
Fig. 3 shows the calcspar of the LED drive circuit of product for being applicable to according to an embodiment of the invention large scale liquid crystal, and Fig. 4 is the circuit diagram of LED drive circuit shown in Fig. 3.Please be simultaneously referring to Fig. 3 and Fig. 4, large scale liquid crystal shows that product need to be used high-powered LED lamp source conventionally, and this high-powered LED lamp source is consisted of LED lamp string LB1～LBn conventionally, and each LED lamp string comprises the LED of a plurality of coupled in series, and wherein n is positive integer.When n is greater than 1, these LED lamp strings LB1～LBn adopts parallel way to drive.LED drive circuit 2 is for driving LED lamp string LB1～LBn, and it comprises main power circuit 21, standby power circuit 22, reference voltage source circuit 23, n constant-current source circuit 241～24n, LED feedback control circuit 25, LED short-circuit protection circuit 26 and adjusting control circuit 27.
LED drive circuit 2 receives the stable DC bus voltage Vbus that electric main produces after over commutation, power factor correction and filtering, is generally about 400V left and right.Bus voltage Vbus produces main power voltage Vm1 and Vm2 after the step-down of main power circuit 21, for example: be respectively 86V and 12V.Wherein, the input that main power voltage Vm1 is used for directly exporting LED lamp string LB1～LBn to is as lamp string input voltage, and so only the power supply conversion efficiency through primary energy conversion will improve.Main power voltage Vm2 is for providing liquid crystal display product inner as required power supplys such as message circuit and liquid crystal panel drive circuits.Bus voltage Vbus separately produces standby power voltage Vsb after the step-down of standby power circuit 22, for example: be 5V, for providing the inner as mainboard micro controller of liquid crystal display product etc. still to need the required power supply of assembly of work under standby mode, and provide reference voltage source circuit 23 and the required power supply of adjusting control circuit 27.
Reference voltage source circuit 23 comprises transistor Q1, shunt regulator U23, resistor R3～R5 and capacitor C4, for receiving the power supply of standby power voltage Vsb and producing according to this reference voltage Vr1 accurately.When shunt regulator U23 adopts TL431, Vr1=2.5V * (R4+R5)/R5.Reference voltage source circuit 23 also comprises resistor R6 and R7, for further producing the reference voltage Vr that is less than 1.25V, Vr=Vr1 * R7/ (R6+R7).
Constant-current source circuit 241～24n is coupled to respectively the output of LED lamp string LB1～LBn, for controlling LED lamp string LB1～LBn current constant and equal and opposite in direction when working.Each constant-current source circuit 24i comprises transistor Mi, operational amplifier OPi and resistor Rsi, and wherein, i is arbitrary positive integer in 1～n.Transistor Mi has first end, the second end and control end, and in this example, transistor Mi is N channel field effect transistor, and its first end, the second end and control end are respectively drain electrode end, source terminal and gate terminal.The drain electrode end of transistor Mi and source terminal are coupled to respectively the output of LED lamp string LBi and the first end of resistor Rsi, and the second end of resistor Rsi is coupled to ground, therefore transistor Mi and resistor Rsi coupled in series are between the output and ground of corresponding LED lamp string LBi.Operational amplifier OPi has positive power source terminal, negative power end, positive input terminal, negative input end and output, power supply and negative power end that its positive power source terminal receives internal supply voltage Vcc are coupled to ground, the first end that the reference voltage Vr that is less than 1.25V that positive input terminal reception reference voltage source circuit 23 produces and negative input end are coupled to resistor Rsi is with the cross-pressure of detecting resistor Rsi, this cross-pressure is corresponding to the operating current of LED lamp string LBi, therefore operational amplifier OPi is by cross-pressure and the reference voltage Vr of comparison resistance device Rsi, so that output signal to the gate terminal of transistor Mi falls to adjust drain-source extreme pressure from its output, making constant and its value of the operating current of LED lamp string LBi is Ilbi=Vr/Rsi.When Vr=0.3V, Ilbi=150mA, the resistance value of resistor Rsi is got 2 Ω.Constant-current source circuit 241～24n, because adopting the power consumption that can reduce the resistor Rs1～Rsn being wherein coupled between transistor AND gate ground compared with low reference voltage Vr, is equivalent to improve power supply conversion efficiency.
LED feedback control circuit 25 comprises transistor Q2, the 3rd sampling resistor Rf3, operational amplifier OP, resistor R8～R14 and the capacitor C5 as switch.Transistor Q2 has first end, the second end and control end, its first end and the second end are coupled to respectively the first end of feedback end FB and the 3rd sampling resistor Rf3, and the second end of the 3rd sampling resistor Rf3 is coupled to ground, pretend as the transistor Q2 of switch and the 3rd sampling resistor Rf3 coupled in series are between feedback end FB and ground.Supply power voltage Vcc and negative power end that the positive power source terminal of operational amplifier OP receives light adjusting circuit 27 outputs are coupled to ground, and positive input terminal reception compensation point voltage and negative input end are coupled to link FB1 and to be coupled to respectively the output of LED lamp string LB1～LBn by diode D11～D1n, bring in the output end voltage of detecting LED lamp string LB1～LBn.Wherein, the value of compensation point voltage is VR9 * (R12+R13+R14)/(R11+R12+R13+R14), and the cross-pressure VR9=Vr1 of resistor R9 * [R9//(R11+R12+R13+R14)]/[R8+R9//(R11+R12+R13+R14)].
Operational amplifier OP is by the compensation point voltage that in the output end voltage of LED lamp string LB1～LBn that relatively negative input end detects, the lowest and positive input terminal receive, so that the control end that outputs signal to transistor Q2 from its output is to control its conducting or disconnection.When in the output end voltage that detects LED lamp string LB1～LBn, the lowest is less than compensation point voltage, when the output end voltage that detects arbitrary LED lamp string is less than compensation point voltage, representing to drop in a certain constant-current source circuit transistorized drain-source extreme pressure falls on the low side and has from being originally normally operated in constant current district and become and be operated in variable resistor district and cannot do the risk that constant current is controlled to LED lamp string, now operational amplifier OP controls transistor Q2 conducting, the the second sampling resistor Rf2 that makes to export in feedback control circuit 213 is equivalent to and a resistor R coupled in parallel, this resistor R=Rds2+Rf3, wherein, Rds2 is the drain electrode end of transistor Q2 and the conduction resistance value of source terminal, therefore main power voltage Vm1=2.5V * (Rf1+Rf2//R)/(Rf2//R), main power voltage Vm1 rises, making to drop to pressure drop in all constant-current source circuit 241～24n all can normally work in rational state and LED lamp string LB1～LBn is done to constant current control.Otherwise, when detecting the output end voltage of LED lamp string LB1～LBn while being all greater than compensation point voltage, represent to drop to pressure drop in all constant-current source circuit 241～24n and all in rational state, can normally work and LED lamp string LB1～LBn is done to constant current control, now operational amplifier OP controls transistor Q2 and disconnects.
LED short-circuit protection circuit 26 comprises Zener (Zener) diode ZD1 and ZD2, resistor R15 and R16 and capacitor C6.The cathode terminal of Zener diode ZD1 is coupled to link DET1 and to be coupled to respectively the output of LED lamp string LB1～LBn by diode D21～D2n, brings in the output end voltage of detecting LED lamp string LB1～LBn, and resistor R15 and R16 coupled in series are between the anode tap and ground of Zener diode ZD1.The two ends of capacitor C6 are coupled to respectively the two ends of resistor R16, and capacitor C6 is for filtering high-frequency noise.The cathode terminal of Zener diode ZD2 and anode tap are coupled to respectively the two ends of resistor R16; and the cathode terminal of Zener diode ZD2 is also coupled to protection end DET to be coupled to mainboard micro controller; Zener diode ZD2 is for doing the voltage clamping of protection end DET; take and guarantee that dim signal Dim is when low level makes transistor M1 in constant-current source circuit 241～24n～Mn cut-off, protection end DET voltage can not surpass the maximum withstand voltage of mainboard micro controller corresponding pin.Wherein, the value of protection point voltage is (Vdet1-Vz1) * R16/ (R15+ R16); Vz1 is the breakdown voltage of Zener diode ZD1, and Vdet1 is that in link DET1 voltage and its value output end voltage that is LED lamp string LB1～LBn, soprano deducts the diode forward conducting voltage that it couples.
When LED lamp string LB1～LBn conducting is worked; when in the output end voltage that detects LED lamp string LB1～LBn, soprano is greater than protection point voltage; the output end voltage that detects arbitrary LED lamp string is greater than while protecting point voltage; representing that LED short circuit number in a certain LED lamp string causes too much drops to transistorized drain-source extreme pressure in corresponding constant-current source circuit and falls higher and increase this crystalline substance this pipe power consumption itself and occur this transistorized risk of overheated final breaking-up; now protection end DET voltage is high levle, is equivalent to output protection signal to mainboard micro controller.Otherwise; when detecting the output end voltage of LED lamp string LB1～LBn, be all less than protection during point voltage; represent that LED short circuit number in all LED lamp string LB1～LBn is all within the scope of default value and be unlikely to make this crystalline substance this pipe itself to increase too many power consumption and occur the transistorized risk of overheated final breaking-up; now protection end DET voltage is low level, is equivalent to not output protection signal to mainboard micro controller.
Adjusting control circuit 27 comprises transistor Q3 and Q4 and resistor R17～R19, for receiving dim signal Dim and controlling according to this constant-current source circuit 241～24n and work with off position to realize burst mode light dimming.When dim signal Dim is high levle, the equal conducting of transistor Q3 and Q4, the standby power voltage Vsb that the emitter-base bandgap grading end of transistor Q4 receives can be sent to the collector terminal of transistor Q4 and export supply power voltage Vcc, Vcc=Vsb-Vec4, wherein, pressure drop when Vec4 is transistor Q4 conducting between emitter-base bandgap grading end and collector terminal, makes its work therefore supply power voltage Vcc powers to constant-current source circuit 241～24n and LED feedback control circuit 25, and then makes LED lamp string LB1～LBn work.Otherwise, when dim signal Dim is low level, transistor Q3 and Q4 all disconnect, the standby power voltage Vsb that the emitter-base bandgap grading end of transistor Q4 receives cannot be sent to the collector terminal of transistor Q4 and no longer export supply power voltage Vcc, therefore constant-current source circuit 241～24n and LED feedback control circuit 25 no longer include power supply and quit work, and then LED lamp string LB1～LBn is quit work.Therefore, the time scale of high levle and low level by dim signal Dim, can control constant-current source circuit 241～24n work and idle time scale, and then control LED lamp string LB1～LBn and work and idle time scale, to reach, control the mean flow rate that LED lamp string LB1～LBn sends light, this is burst mode light dimming.
The exportable switching signal of mainboard micro controller (On/Off) and dim signal (Dim).Wherein, switching signal (On/Off), for close PWM controller U12 under standby mode, makes it energy saving more under standby mode.Dim signal Dim is for controlling constant-current source circuit 241～24n work and off position to realize burst mode light dimming by adjusting control circuit 27.And, whether mainboard micro controller only can be set as (when LED lamp string LB1～LBn normally works) judgement protection end DET when dim signal Dim is high levle and be high levle or receive guard signal, once protection end, DET is high levle or receives guard signal, mainboard micro controller is exported at once one and is continued low level signal to adjusting control circuit 27, make adjusting control circuit 27 stop exporting supply power voltage Vcc to constant-current source circuit 241～24n and LED feedback control circuit 25, and then LED lamp string LB1～LBn and LED feedback control circuit 25 are quit work, not destroyed with electronic components such as protection constant-current source internal transistors.
Although the present invention discloses as above with preferred embodiment; so it is not intended to limit the present invention; anyly have the knack of this skill person; without departing from the spirit and scope of the present invention; when doing a little change and retouching, so protection scope of the present invention is when being as the criterion depending on the accompanying claim person of defining.
Claims (7)
1. a LED driving circuit, is characterized in that, comprising:
One main power circuit, this main power circuit comprises a main power source transducer and an output feedback control circuit, this main power source transducer receives electric main through rectification, also produce according to this main power voltage exports the input of n LED light string to the bus voltage producing after power factor correction and filtering from the output of this main power circuit, output feedback control circuit comprises the first sampling resistor Rf1, the second sampling resistor Rf2, resistor R1, resistor R2, capacitor C3, shunt regulator U22, optical coupler U3 and PWM controller U12, wherein, the first sampling resistor Rf1 is coupled between the output and feedback end FB of main power circuit 21, the second sampling resistor Rf2 is coupled between feedback end FB and ground, one end of described capacitor C3 is connected with described feedback end FB, and the other end is connected with one end of described resistor R2, the other end of described resistor R2 is connected with the second end of optical coupler U3 and the first end of shunt regulator U22, the control end of described shunt regulator U22 is connected with described feedback end FB, the second end ground connection of described shunt regulator U22, the second end of described optical coupler U3 is connected with the output of described main power source transducer through resistor R1, the 3rd end of described optical coupler U3 is connected with described output feedback control circuit, the 4th end ground connection, this output feedback control circuit is adjusted this main power voltage according to this main power source transducer of this feedback end voltage control, and wherein n is positive integer,
One light-emitting diode feedback control circuit, is coupled to the output of described LED light string, comprises transistor Q2, the 3rd sampling resistor Rf3, operational amplifier OP, resistor R8～R14 and capacitor C5 as switch; Transistor Q2 has first end, the second end and control end, its first end and the second end are coupled to respectively the first end of feedback end FB and the 3rd sampling resistor Rf3, and the second end of the 3rd sampling resistor Rf3 is coupled to ground, reference voltage Vr1 is connected with one end of resistor R10 with resistor R8, and the other end of resistor R8 is through resistor R9 ground connection; The negative terminal of another termination operational amplifier OP of resistor R10; One end of the positive termination resistor R11 of described operational amplifier OP and one end of resistor R12, the other end of described resistor R11 is connected with the other end of resistor R8; The other end of described resistor R12 is connected with the output of described operational amplifier OP and one end of resistor R13; The other end of described resistor R13 is connected with the control end of one end of resistor R14, one end of capacitor C 15 and transistor Q2; The other end ground connection of the other end of described resistor R14 and capacitor C 15; When the output end voltage that detects arbitrary LED light string is less than a compensation point voltage, control this switch conduction, otherwise control this switch, disconnect;
N constant-current source circuit, wherein each constant-current source circuit comprises a transistor, an operational amplifier and a resistor, this resistor in series of this transistor AND gate is coupled between the output and ground of a corresponding LED light string, and this operational amplifier is detected the cross-pressure of this resistor and relatively and according to this controlled this transistor with a reference voltage and makes the operating current of this corresponding LED light string constant; And
One adjusting control circuit, is coupled to described constant-current source circuit, receives a dim signal and also controls according to this described constant-current source circuit work and off position to realize burst mode light dimming.
2. LED driving circuit according to claim 1, is characterized in that: described adjusting control circuit is also coupled to this light-emitting diode feedback control circuit, according to this dim signal, whether controls this light-emitting diode feedback control circuit work.
3. LED driving circuit according to claim 1, is characterized in that: also comprise a reference voltage source circuit, this reference voltage source circuit is coupled to those constant-current source circuits, produces this reference voltage that is less than 1.25 volts.
4. LED driving circuit according to claim 1; it is characterized in that: also comprise a light-emitting diode short-circuit protection circuit; this light-emitting diode short-circuit protection circuit is coupled to the output of described LED light string; when those LED light string work; when detecting, when being greater than a protection point voltage, exports the output end voltage of arbitrary LED light string a guard signal; otherwise do not export this guard signal, this guard signal makes this adjusting control circuit control described constant-current source circuit by this dim signal to quit work.
5. LED driving circuit according to claim 4; it is characterized in that: be applicable to a liquid crystal display product; this liquid crystal display product comprises a mainboard micro controller; this mainboard micro controller is coupled to this adjusting control circuit and this light-emitting diode short-circuit protection circuit, exports this dim signal and by this dim signal, make this adjusting control circuit control those constant-current source circuits when receiving this guard signal to quit work.
6. LED driving circuit according to claim 5, is characterized in that: also comprise a standby power circuit, this standby power circuit receives this bus voltage and produces according to this standby power power voltage supply to this mainboard micro controller.
7. LED driving circuit according to claim 5, is characterized in that: described liquid crystal display product comprises liquid crystal display or LCD TV.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201210136261.7A CN102711321B (en) | 2012-05-04 | 2012-05-04 | Light emitting diode driving circuit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201210136261.7A CN102711321B (en) | 2012-05-04 | 2012-05-04 | Light emitting diode driving circuit |
Publications (2)
| Publication Number | Publication Date |
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| CN102711321A CN102711321A (en) | 2012-10-03 |
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