CN202632722U - LED drive circuit - Google Patents
LED drive circuit Download PDFInfo
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- CN202632722U CN202632722U CN 201220197476 CN201220197476U CN202632722U CN 202632722 U CN202632722 U CN 202632722U CN 201220197476 CN201220197476 CN 201220197476 CN 201220197476 U CN201220197476 U CN 201220197476U CN 202632722 U CN202632722 U CN 202632722U
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Abstract
The utility model relates to an LED (Light Emitting Diode) drive circuit, comprising a main power supply circuit, a reference voltage source circuit, constant current source circuits, an LED feedback control circuit, an LED short circuit protection circuit, and a light modulation control circuit; wherein the main power supply circuit receives a bus voltage and generates a main power supply voltage according to the bus voltage, then directly provides an operating voltage required by LED light strings, the constant current source circuit adopts an operational amplifier to receive a lower reference voltage generated by the reference voltage source circuit in order to make comparison with a voltage corresponding to an operating current of the LED light string, thus a power supply conversion efficiency can be raised; the LED feedback control circuit performs corresponding adjustments for the main power supply voltage, in order to ensure that the voltage drop in the constant current source circuit is reasonable so that constant current control can be performed for the LED light string; the LED short circuit protection circuit controls all the constant current source circuits to shut down when an overloaded output end voltage is caused by short circuit occurring on an LED in the LED light string, in order to protect a transistor in the constant current source from being damaged by an overheating problem.
Description
Technical field
The utility model relates to a kind of light emitting diode (Light-Emitting Diode, LED) driving circuit, and particularly relevant for a kind of led drive circuit that is applicable to the 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 often is applied in.See also Fig. 1, large scale liquid crystal shows that product need use the high-powered LED lamp source usually, and this high-powered LED lamp source is made up of LED lamp string LB1～LBn usually, and each LED lamp string comprises the LED of a plurality of coupled in series, and wherein n is a positive integer.When n greater than 1 the time, these LED lamp strings LB1～LBn adopts parallel way to drive.Led drive circuit 1 is used 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 receive electric main through overcommutation, power factor correction (Power Factor Corrector, PFC) with filtering after the stable dc bus voltage Vbus that produces, generally be about 400 volts (volt, V).Bus voltage Vbus for example is respectively 24V and 12V through producing main power voltage Vm1 and Vm2 after the step-down of main power circuit 11.Wherein, Main power voltage Vm1 is used for being slightly larger than through the back generation of boosting of voltage up converting circuit 13 the fluorescent tube input voltage vin of the required WV of LED lamp string again; For example: LED lamp tube ends voltage is 85V during work; Offering lamp string input voltage after then voltage up converting circuit boosts is 86V, to export the input end of LED lamp string LB1～LBn to.Main power voltage Vm2 then is used to provide liquid crystal display product inner like required power supplys such as message circuit (Audio Circuit) and liquid crystal panel (Panel) driving circuits.Bus voltage Vbus is in addition through producing standby power voltage Vsb after the step-down of standby power circuit 12; For example be: 5V; (Micro Control Unit MCU) waits the required power supply of assembly that under standby mode, still needs work like the mainboard micro controller to be used to provide liquid crystal display product inside.
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, is used for converting the required higher relatively work input voltage of each LED lamp string into importing lower direct current.Output filter circuit comprises capacitor C1, is used to reduce the output voltage ripple of boost converter.The output feedback control circuit comprises PWM (Pulse-Width Modulation; PWM) controller U11 is used for coming the output voltage (being lamp string input voltage vin in this example) of the switch responsibility cycle of oxide-semiconductor control transistors Q1 with the adjustment boost converter according to the output voltage of LED feedback control circuit 15.Constant-current source circuit 141～14n is coupled to the output terminal of LED lamp string LB1～LBn respectively, is used to control LED lamp string LB1～LBn current constant and equal and opposite in direction when work.See also Fig. 2, it is the existing normal circuit diagram that adopts the constant-current source circuit of the adjustable shunt regulator of three ends.With constant-current source circuit 141 is example, the shunt regulator U21 that it comprises transistor Q2, resistor R 1～R3 and has anode tap A, cathode terminal K and reference edge R.When shunt regulator U21 adopt 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 working current Ilb1 of LED lamp string LB1 is Ilb1=1.25V/R1.
Please again referring to Fig. 1 and cooperate Fig. 2; If the output end voltage of LED lamp string is low excessively, drain electrode end and the pressure drop between the source terminal (calling the drain-source extreme pressure in the following text falls) that then drops to transistor Q2 in the constant-current source circuit can be on the low side and become in the constant current district by the script operate as normal and to be operated in the variable resistor district and can't to do constant current control to LED lamp string, wherein; Vgs when working in the constant current district>Vth and Vds>Vgs-Vth; Vgs when working in the variable resistor district>Vth and Vds Vgs-Vth, wherein, Vgs is the gate terminal of transistor Q2 and the pressure drop between the source terminal; Vds is that the drain-source extreme pressure of transistor Q2 falls, and Vth is the cut-in voltage (threshold voltage) of transistor Q2.Therefore; LED feedback control circuit 15 is through 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 the output end voltage that is detected, make the pressure drop that drops among all constant-current source circuit 141～14n all be in rational state and can operate as normal do constant current control LED lamp string LB1～LBn.In addition, if the LED short circuit number in the LED lamp string is too many, the drain-source extreme pressure that then drops to transistor Q2 in the constant-current source circuit fall can be higher and increase power consumption or even because of electric transistor Q2 because of the overheated transistor Q2 that damages.Therefore; LED short-circuit protection circuit 16 is through the output end voltage of diode D21～D2n detecting LED lamp string LB1～LBn; And in the output end voltage that is detected the soprano greater than protection during point voltage; Close PWM controller U1, make voltage up converting circuit 13 no longer do boost conversion, do not damaged with the electronic components such as transistor of protecting constant-current source circuit.
Exportable switching signal of mainboard micro controller (On/Off) and dim signal (Dim).Wherein, switching signal (On/Off) is used under standby mode, closing PWM controller U1, makes it energy saving more under standby mode.Dim signal (Dim) is used for through adjusting control circuit 17 141～14n work of control constant-current source circuit and off positions; And then control LED lamp string LB1～LBn work and off position; To reach the mean flow rate that control LED lamp string LB1～LBn sends light, this is burst mode (burst mode) light modulation.
Existing led drive circuit 1 adopts bus voltage Vbus to produce lamp string input voltage vin so that LED lamp string LB1～LBn to be provided required WV through the back of boosting of voltage up converting circuit 13 again through the step-down of main power circuit 11 earlier, and the power supply conversion efficiency through twice energy conversion will reduce like this.Secondly; Constant-current source circuit 141～14n usually adopts as the shunt regulator U21 of AZ432, and its reference edge R voltage is stabilized in 1.25V, when the working current of LED lamp string greatly the time; The resistor R 1 that is coupled between reference edge R and the ground will have bigger power consumption, be equivalent to reduce power supply conversion efficiency.
Summary of the invention
The purpose of the utility model 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 purpose, the utility model 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 a positive integer.Main power circuit comprises primary power converter and output feedback control circuit.The bus voltage that primary power converter reception electric main produces after rectification, power factor correction and filtering also produces main power voltage exports n LED lamp string to from the output terminal of main power circuit input end according to this.The output feedback control circuit comprises the first sample resistance device and the second sample resistance device; The first sample resistance device is coupled between the output terminal and feedback end of main power circuit; The second sample resistance device is coupled between feedback end and the ground, and the output feedback control circuit is according to feedback end Control of Voltage primary power converter adjustment main power voltage.The LED feedback control circuit is coupled to the output terminal of said LED lamp string; Comprise that switch and the 3rd sample resistance device coupled in series are between feedback end and ground; The output end voltage that detects arbitrary LED lamp string less than compensation point voltage time control switch conduction, otherwise then CS breaks off.Each constant-current source circuit comprises transistor, operational amplifier and resistor; The transistor AND gate resistor in series is coupled between the output terminal and ground of corresponding LED lamp string, and the cross-pressure of operational amplifier detecting resistor and with the reference voltage comparison and according to this oxide-semiconductor control transistors make the working current of corresponding LED lamp string constant.Adjusting control circuit is coupled to said constant-current source circuit, receives dim signal and also controls said constant-current source circuit work and off position according to this to realize the burst mode light modulation.
In the utility model one embodiment, adjusting control circuit also is coupled to the LED feedback control circuit, whether controls the work of LED feedback control circuit according to dim signal.
In the utility model one embodiment, led drive circuit also comprises the reference voltage source circuit.The reference voltage source circuit is coupled to said constant-current source circuit, produces the reference voltage less than 1.25 volts.
In the utility model one embodiment, led drive circuit also comprises the LED short-circuit protection circuit.The LED short-circuit protection circuit is coupled to the output terminal of said LED lamp string; When LED lamp string is worked; When the output end voltage that detects arbitrary LED lamp string greater than protection output protection signal during point voltage; Otherwise output protection signal not then, wherein, guard signal makes adjusting control circuit control said constant-current source circuit through dim signal and quits work.
In the utility model one embodiment, led drive circuit is applicable to liquid crystal display product, for example LCD or LCD TV etc.Liquid crystal display product comprises the mainboard micro controller.The mainboard micro controller is coupled to adjusting control circuit and LED short-circuit protection circuit, exports dim signal and when receiving guard signal, make adjusting control circuit control said constant-current source circuit through dim signal to quit work.
In the utility model one embodiment, led drive circuit also comprises the standby power circuit.The standby power circuit receives bus voltage and produces the standby power power voltage supply according to this gives the mainboard micro controller.
The input end that the main power voltage that the led drive circuit of the utility model produces after the voltage transitions of main power circuit because of the employing bus voltage passes through directly exports LED lamp string to is to provide LED lamp string required WV, and so only the power supply conversion efficiency through the primary energy conversion will improve; Secondly, the lower reference voltage that adopts operational amplifier to receive to be produced by the reference voltage source circuit because of constant-current source circuit to be doing comparison with the corresponding voltage of LED lamp string working current, thereby can reduce the power consumption of constant-current source circuit.In addition, the led drive circuit of the utility model also adopts the LED feedback control circuit that main power voltage is adjusted accordingly, and makes the pressure drop that drops in the constant-current source circuit all be in rational state and can operate as normal do constant current control to LED lamp string; And adopt the LED short-circuit protection circuit to detect each LED lamp string output end voltage whether the protection point that exceeds the estimates fixed is arranged; When the LED short-circuit protection circuit detects a certain LED lamp string output end voltage in work, surpassing the protection point that presets; The dim signal output port of mainboard micro controller will be exported one and continue low level signal to adjusting control circuit; Use the inner transistor of constant-current source circuit to be closed, the electric transistor inner with the protection constant-current source circuit do not damaged because of overheated.
For let the above-mentioned of the utility model and other purpose, feature and advantage can be more obviously understandable, hereinafter is special lifts preferred embodiment, and cooperates appended graphicly, elaborates as follows.
Description of drawings
Fig. 1 is a kind of existing calcspar that large scale liquid crystal shows the led drive circuit of product that often is applied in.
Fig. 2 is the existing normal circuit diagram that adopts the constant-current source circuit of the adjustable shunt regulator of three ends shown in Figure 1.
Fig. 3 shows the calcspar of the led drive circuit of product for the large scale liquid crystal that is applicable to according to the utility model one embodiment.
Fig. 4 is the circuit diagram of led drive circuit shown in Figure 3.
[primary clustering symbol description]
1:LED driving 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 driving circuit 21: main power circuit
211: primary power converter 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 sample resistance device Rf2: the second sample resistance device
Rf3: the 3rd sample resistance device Rs1～Rsn: resistor
U11, U12:PWM controller U21～U23: shunt regulator
U3: photo-coupler ZD1, ZD2: Zener diode
A: the anode tap K of shunt regulator: the cathode terminal of shunt regulator
R: the reference edge DET1 of shunt regulator, FB1: 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 the large scale liquid crystal that is applicable to according to the utility model one embodiment, and Fig. 4 is the circuit diagram of led drive circuit shown in Figure 3.Please be simultaneously referring to Fig. 3 and Fig. 4, large scale liquid crystal shows that product need use the high-powered LED lamp source usually, and this high-powered LED lamp source is made up of LED lamp string LB1～LBn usually, and each LED lamp string comprises the LED of a plurality of coupled in series, and wherein n is a positive integer.When n greater than 1 the time, these LED lamp strings LB1～LBn adopts parallel way to drive.Led drive circuit 2 is used 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 overcommutation, power factor correction and filtering, generally be about about 400V.Bus voltage Vbus is through producing main power voltage Vm1 and Vm2, for example: be respectively 86V and 12V after the step-down of main power circuit 21.Wherein, the input end 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 the primary energy conversion will improve.Main power voltage Vm2 then is used to provide liquid crystal display product inner like required power supplys such as message circuit and liquid crystal panel drive circuits.Bus voltage Vbus is in addition through producing standby power voltage Vsb after the step-down of standby power circuit 22; For example: be 5V; Be used to provide the inner as mainboard micro controller of liquid crystal display product etc. under standby mode, still to need the required power supply of assembly of work, and reference voltage source circuit 23 and adjusting control circuit 27 required power supplys are provided.
Main power circuit 21 comprises primary power converter 211, output filter circuit 212 and output feedback control circuit 213.Wherein, Primary power converter 211 for example is step-down (buck) converter; Be used to receive the bus voltage Vbus that electric main produces after rectification, power factor correction and filtering, and produce main power voltage Vm1 exports LED lamp string LB1～LBn to from the output terminal of main power circuit 21 input end according to this.Output filter circuit 212 comprises capacitor C1 and C2 and inductor L1, is used to reduce the main power voltage Vm1 ripple of primary power converter 211 outputs.Output feedback control circuit 213 comprises the first sample resistance device Rf1, the second sample resistance device Rf2, resistor R 1 and R2, capacitor C3, shunt regulator U22, photo-coupler U3 and PWM controller U12; Wherein, The first sample resistance device Rf1 is coupled between the output terminal and feedback end FB of main power circuit 21, and the second sample resistance device Rf2 is coupled between feedback end FB and the ground.Output feedback control circuit 213 is through the first sample resistance device Rf1 and second sample resistance device Rf2 detecting main power voltage Vm1; Feedback end FB voltage is promptly corresponding to the main power voltage Vm1 that detects, and is sent to PWM controller U12 through photo-coupler U3 again after this feedback end FB voltage amplifies error through shunt regulator U22 and adjusts main power voltage Vm1 with the switch responsibility cycle (duty) in the control primary power converter 211 and make it stable.When shunt regulator U22 adopted TL431, its inside had the reference voltage source of a 2.5V, and reference edge R voltage will be stabilized in 2.5V, thus main power voltage Vm1=2.5V * (Rf1+Rf2)/Rf2.
Reference voltage source circuit 23 comprises transistor Q1, shunt regulator U23, resistor R 3～R5 and capacitor C4, is used to receive the power supply of standby power voltage Vsb and produces reference voltage Vr1 accurately according to this.When shunt regulator U23 adopts TL431, Vr1=2.5V * (R4+R5)/R5.Reference voltage source circuit 23 also comprises resistor R 6 and R7, is used for further producing the reference voltage Vr less than 1.25V, Vr=Vr1 * R7/ (R6+R7).
Constant-current source circuit 241～24n is coupled to the output terminal of LED lamp string LB1～LBn respectively, is used to control LED lamp string LB1～LBn current constant and equal and opposite in direction when work.Each constant-current source circuit 24i comprises transistor Mi, operational amplifier OPi and resistor R si, and wherein, i is arbitrary positive integer among 1～n.Transistor Mi has first end, second end and control end, and in this example, transistor Mi is a N channel field effect transistor, and its first end, 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 the output terminal of LED lamp string LBi and first end of resistor R si respectively; And second end of resistor R si is coupled to ground, so transistor Mi and resistor R si coupled in series are between the output terminal 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 terminal; Power supply and negative power end that its positive power source terminal receives internal supply voltage Vcc are coupled to ground; First end that reference voltage Vr and the negative input end less than 1.25V that positive input terminal reception reference voltage source circuit 23 produces is coupled to resistor R si is with the cross-pressure of detecting resistor R si; This cross-pressure is corresponding to the working current of LED lamp string LBi; So operational amplifier OPi is through cross-pressure and the reference voltage Vr of comparison resistance device Rsi; So that the gate terminal that outputs signal to transistor Mi from its output terminal is fallen with adjustment drain-source extreme pressure, making constant and its value of the working current of LED lamp string LBi is Ilbi=Vr/Rsi.When Vr=0.3V, Ilbi=150mA, the resistance value of resistor R si is got 2 Ω.Constant-current source circuit 241～24n can reduce the power consumption of the resistor R s1～Rsn that wherein is coupled between the transistor AND gate ground because of adopting lower reference voltage Vr, is equivalent to improve power supply conversion efficiency.
LED feedback control circuit 25 comprises transistor Q2, the 3rd sample resistance device Rf3, operational amplifier OP, resistor R 8～R14 and the capacitor C5 as switch.Transistor Q2 has first end, second end and control end; Its first end and second end are coupled to first end of feedback end FB and the 3rd sample resistance device Rf3 respectively; And second end of the 3rd sample resistance device Rf3 is coupled to ground, pretend into the transistor Q2 of switch and the 3rd sample resistance device Rf3 coupled in series between feedback end FB and ground.Supply 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 receives compensation point voltage and negative input end is coupled to link FB1 brings in detecting LED lamp string LB1～LBn with the output that is coupled to LED lamp string LB1～LBn through diode D11～D1n respectively output end voltage.Wherein, the value of compensation point voltage is VR9 * (R12+R13+R14)/(R11+R12+R13+R14), and the cross-pressure VR9=Vr1 of resistor R 9 * [R9//(R11+R12+R13+R14)]/[R8+R9//(R11+R12+R13+R14)].
Operational amplifier OP is through the compensation point voltage that the lowest and positive input terminal received in the output end voltage that compares LED lamp string LB1～LBn that negative input end detected, so that the control end that outputs signal to transistor Q2 from its output terminal is to control its conducting or disconnection.When the lowest is less than compensation point voltage in the output end voltage that detects LED lamp string LB1～LBn; The output end voltage that promptly detects arbitrary LED lamp string is during less than compensation point voltage; Expression drops to transistorized drain-source extreme pressure in a certain constant-current source circuit and falls on the low side and have by the script operate as normal and become the risk that is operated in the variable resistor district and can't does constant current control to LED lamp string in the constant current district; Operational amplifier OP oxide-semiconductor control transistors Q2 conducting this moment; The second sample resistance device Rf2 in the output 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; So main power voltage Vm1=2.5V * (Rf1+Rf2//R)/(Rf2//R), main power voltage Vm1 rises, make the pressure drop that drops among all constant-current source circuit 241～24n all be in rational state and can operate as normal do constant current control LED lamp string LB1～LBn.Otherwise; When the output end voltage that detects LED lamp string LB1～LBn during all greater than compensation point voltage; The pressure drop that expression drops among all constant-current source circuit 241～24n all is in rational state and can operate as normal does constant current control to LED lamp string LB1～LBn, and this moment, operational amplifier OP oxide-semiconductor control transistors Q2 broke off.
LED short-circuit protection circuit 26 comprises Zener (Zener) diode ZD1 and ZD2, resistor R 15 and R16 and capacitor C6.The cathode terminal of Zener diode ZD1 is coupled to link DET1 and brings in the output end voltage of detecting LED lamp string LB1～LBn with the output that is coupled to LED lamp string LB1～LBn through diode D21～D2n respectively, and resistor R 15 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 the two ends of resistor R 16 respectively, and capacitor C6 is used for the filtering high frequency noise.The cathode terminal of Zener diode ZD2 and anode tap are coupled to the two ends of resistor R 16 respectively; And the cathode terminal of Zener diode ZD2 also is coupled to protection end DET to be coupled to the mainboard micro controller; Zener diode ZD2 is used to do the voltage clamp of protection end DET; With guarantee dim signal Dim be low level make among constant-current source circuit 241～24n transistor M1～Mn by the time, 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 disruptive voltage of Zener diode ZD1, and Vdet1 is that link DET1 voltage and its value deduct the diode forward forward voltage that it couples for soprano in the output end voltage of LED lamp string LB1～LBn.
When LED lamp string LB1～LBn conducting is worked; When soprano in the output end voltage that detects LED lamp string LB1～LBn greater than protection during point voltage; The output end voltage that promptly detects arbitrary LED lamp string is during greater than the protection point voltage; Representing that LED short circuit number in a certain LED lamp string causes too much drops in the corresponding constant-current source circuit transistorized drain-source extreme pressure and falls higher and increase should crystalline substance this pipe power consumption itself and this transistorized risk of overheated final breaking-up occurs; Protection this moment end DET voltage is high levle, is equivalent to output protection signal to mainboard micro controller.Otherwise; When the output end voltage that detects LED lamp string LB1～LBn all less than protection during point voltage; Represent that a LED short circuit number average among all LED lamp string LB1～LBn is in the default value scope and be unlikely to make this crystalline substance this pipe itself to increase too many power consumption and the transistorized risk of overheated final breaking-up occurs; Protection this moment 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 R 17～R19, is used to receive dim signal Dim and controls constant-current source circuit 241～24n work and off position according to this to realize the burst mode light modulation.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 received of transistor Q4 can be sent to the collector terminal of transistor Q4 and export supply voltage Vcc, Vcc=Vsb-Vec4; Wherein, Pressure drop when Vec4 is transistor Q4 conducting between emitter-base bandgap grading end and the collector terminal makes its work so supply voltage Vcc supplies power 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 break off; The standby power voltage Vsb that the emitter-base bandgap grading end received of transistor Q4 can't be sent to the collector terminal of transistor Q4 and no longer export supply voltage Vcc, supplies power and quits work so constant-current source circuit 241～24n and LED feedback control circuit 25 no longer include, and then LED lamp string LB1～LBn is quit work.Therefore; The time scale of high levle and low level through dim signal Dim; Be may command constant-current source circuit 241～24n work and idle time scale; And then control LED lamp string LB1～LBn work and idle time scale, to reach the mean flow rate that control LED lamp string LB1～LBn sends light, this is the burst mode light modulation.
Exportable switching signal of mainboard micro controller (On/Off) and dim signal (Dim).Wherein, switching signal (On/Off) is used under standby mode, closing PWM controller U12, makes it energy saving more under standby mode.Dim signal Dim is used for through adjusting control circuit 27 control constant-current source circuits 241～24n work and off position to realize the burst mode light modulation.And; The mainboard micro controller only can be set at when dim signal Dim is high levle when LBn operate as normal (LED lamp string LB1～) and judge whether protection end DET is high levle or receives guard signal; In case protection end DET is a high levle or when receiving guard signal; The mainboard micro controller is exported one at once and is continued low level signal to adjusting control circuit 27; Make adjusting control circuit 27 stop to export supply voltage Vcc and give 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, do not damaged with electronic components such as protection constant current source internal transistors.
Though the utility model discloses as above with preferred embodiment; So it is not to be used to limit the utility model; Anyly have the knack of this art; In spirit that does not break away from the utility model and scope, when can doing a little change and retouching, so the protection domain of the utility model is as the criterion when looking accompanying the 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 primary power converter and an output feedback control circuit; The bus voltage that this primary power converter reception electric main produces after rectification, power factor correction and filtering also produces a main power voltage exports n LED light string to from the output terminal of this main power circuit input end according to this; This output feedback control circuit comprises one first sample resistance device and one second sample resistance device; This first sample resistance device is coupled between the output terminal and a feedback end of this main power circuit; This second sample resistance device is coupled between this feedback end and the ground, and this output feedback control circuit is according to this this main power voltage of primary power converter adjustment of this feedback end Control of Voltage, and wherein n is a positive integer;
One light emitting diode feedback control circuit; Be coupled to the output terminal of said LED light string; Comprise that a switch and one the 3rd sample resistance device coupled in series are between this feedback end and ground; Control this switch conduction at the output end voltage that detects arbitrary LED light string during less than a compensation point voltage, break off otherwise then control this switch;
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 terminal and ground of a corresponding LED light string, and this operational amplifier is detected the cross-pressure of this resistor and also controlled this transistor according to this with a reference voltage comparison and makes the working current of this corresponding LED light string constant; And
One adjusting control circuit is coupled to said constant-current source circuit, receives a dim signal and also controls said constant-current source circuit work and off position according to this to realize the burst mode light modulation.
2. LED driving circuit according to claim 1 is characterized in that: said adjusting control circuit also is coupled to this light emitting diode feedback control circuit, whether controls this light emitting diode feedback control circuit work according to this dim signal.
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 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 terminal of said LED light string; When those LED light string work; When the output end voltage that detects arbitrary LED light string is protected point voltage greater than one, export a guard signal, otherwise then do not export this guard signal, this guard signal makes this adjusting control circuit control said constant-current source circuit through this dim signal and quits 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 when receiving this guard signal, through this dim signal these those constant-current source circuits of adjusting control circuit control is 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 a standby power power voltage supply according to this gives this mainboard micro controller.
7. LED driving circuit according to claim 5 is characterized in that: said liquid crystal display product comprises LCD or LCD TV.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
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