CN207783204U - Led drive circuit - Google Patents

Abstract

This application discloses LED drive circuits.The LED drive circuit includes：Main circuit realizes conversion of the DC input voitage to average anode current using the conducting and disconnection of switching tube；And control circuit, drive signal is provided to the switching tube, to control the conducting state of the switching tube, wherein, the control circuit obtains current detection signal from the main circuit, and peak value comparison method is executed according to the current detection signal and peak point current reference signal, make switching tube switched conductive state in each switch periods of the drive signal, the drive signal has the first duty ratio, the control circuit receives dim signal, and the output of the drive signal is controlled according to the dim signal, the dim signal has the second duty ratio, the control circuit includes peak current compensation module, the peak point current reference signal is compensated according to the second duty ratio of the dim signal, to inhibit light modulation to shake.

Description

LED drive circuit

Technical field

The utility model is related to switch power technologies, more particularly, to light emitting diode (LED) light modulating device and driving Circuit.

Background technology

LED be used for lighting area when, use LED drive circuit adjust brightness with meet user individual demand or It needs to dim to reduce energy consumption according to environment.LED drive circuit be, for example, traditional controllable silicon dimmer or pulsewidth modulation (that is, PWM) light modulating device.The operation principle of controllable silicon dimmer is to adjust output electricity by changing the angle of flow of AC-input voltage Pressure and output current.The operation principle of PWM light modulating devices is to adjust the electricity for flowing through LED by changing the duty ratio of pwm signal Stream.Compared with controllable silicon light modulation, the conduction losses of PWM light modulating devices is low, noise is small and the operation is stable, and can reduce electromagnetism It interferes (EMI).Due to that can reduce the component size of EMI filter circuit, the volume of the LED drive circuit based on PWM light modulations subtracts Small and dimming behavior is excellent.Therefore, application of the PWM light modulations in the lighting area of LED is also more and more extensive.

The light modulation depth of LED drive circuit is rate of change of brightness of the operating brightness of LED relative to complete illuminating state, example As 10%~100% light modulation depth may be implemented in LED drive circuit.In the LED drive circuit using PWM light modulations, with Light modulation depth becomes larger (that is, depth light modulation), and the duty ratio of pwm signal reduces, and brightness jitter is likely to occur in dimming process Problem.

Therefore, it is desirable to further increase the LED drive circuit that is dimmed based on PWM dimming process stability, to subtract Brightness jitter in small dimming process.

Utility model content

In view of this, the purpose of this utility model be to provide it is a kind of according to pwm control signal compensate inductive current peak with Improve the LED drive circuit of dimming effect.

Problem to be solved in the utility model is to provide a kind of PWM depth light regulating technology, is accounted for by detecting pwm control signal Sky adjusts the peak value of inductive current than size.And then it improves when the dimming effect under depth light modulation.Make dimming process LED Lamp brightness change is smoother.It is not in apparent LED luminance jitter phenomenon.And then improve light modulation depth.

One side according to the present utility model provides a kind of LED drive circuit, including：Main circuit, the main circuit include Switching tube realizes conversion of the DC input voitage to average anode current using the conducting and disconnection of switching tube；And control electricity Road is connected with the main circuit, for providing drive signal to the switching tube, to control the conducting shape of the switching tube State, wherein the control circuit obtains current detection signal from the main circuit, and according to the current detection signal and peak It is worth current reference signal and executes peak value comparison method so that the switching tube is cut in each switch periods of the drive signal Conducting state is changed, there is the drive signal the first duty ratio, the control circuit to receive dim signal, and according to the tune Optical signal controls the output of the drive signal, and the dim signal has the second duty ratio, and the control circuit includes peak value Current compensation module compensates the peak point current reference signal, to inhibit to adjust according to the second duty ratio of the dim signal Light jiggle.

Preferably, the dimming cycle of the dim signal is more than the switch periods of the drive signal, and, in each tune In photoperiod, when the dim signal is effective, the control circuit provides the drive signal, invalid in the dim signal When, the control circuit stops providing the drive signal.

Preferably, the control circuit reduces the peak point current reference signal under depth light modulation, to correspondingly subtract The switch periods of the small drive signal.

Preferably, when the duty ratio of the dim signal is less than or equal to desired duty ratio, judge to dim shape in depth State.

Preferably, the expectation duty ratio is 20%.

Preferably, under depth light modulation, the duty ratio of the peak point current reference signal and the dim signal at Direct ratio.

Preferably, the input terminal of the peak current compensation module receives the dim signal, and output end provides compensation letter Number, the peak point current reference signal is the difference signal of predetermined reference and the thermal compensation signal.

Preferably, under depth light modulation, the average anode current of the main circuit and the duty ratio of dim signal are in Nonlinear change.

Preferably, the calculation formula of the average anode current Iout of the main circuit is：

If Dcomp≤D≤1

If 0≤D<Dcomp (formula 1)

Wherein, Vref indicates that peak point current reference signal, Dcomp indicate it is expected that duty ratio, D indicate the second duty ratio, Rs Indicate that sampling resistor, K indicate constant.

Preferably, the peak current compensation module includes：Be connected in series in first resistor between feeder ear and ground and Transistor, the first node between the first resistor and the transistor generate the inversion signal of the dim signal；The Two resistance are connected between the input terminal and the control terminal of the transistor；Potential-divider network, be connected to the first node and Between ground, for being divided to the inversion signal, the potential-divider network has second node；First capacitance is connected to described Between two nodes and ground, for being filtered to the inversion signal, signal is detected to generate duty ratio；And diode, The anode of the diode is connected to the second node, and cathode is connected to the output end, for providing the thermal compensation signal.

Preferably, the potential-divider network includes the 3rd resistor being connected in series with and the 4th resistance, and the second node is institute State the intermediate node of 3rd resistor and the 4th resistance.

Preferably, further include：The 5th resistance being connected in series between the diode and the output end.

Preferably, the peak current compensation module includes：Be connected in series in the first constant-current source between feeder ear and ground, First switch and the first capacitance, the first switch are connected and disconnect under the control of the inversion signal of the dim signal, When the first switch conducting, first constant-current source is to first capacitor charging, in the first switch and described first First node between capacitance generates duty ratio and detects signal；First resistor is connected in parallel with first capacitance, described When one switch disconnects, first capacitance discharges via the first resistor；It is connected in series between the first node and ground Diode and second resistance, second node between the diode and the second resistance generate the first thermal compensation signal； And signal conversion module, it is connected between the second node and the output end, for the first thermal compensation signal to be converted into Second thermal compensation signal.

Preferably, the signal conversion module includes：Current mirror；It is connected in series between the input terminal of current mirror and ground The first transistor and 3rd resistor；The 4th resistance and the 5th resistance being connected in series between the output end of current mirror and ground；With And operational amplifier, the in-phase input end of the operational amplifier are connected to the second node to receive the thermal compensation signal, Inverting input is connected to the third node between the first transistor and the 3rd resistor, wherein the 4th resistance Both ends be connected to the output end, to provide the thermal compensation signal.

Preferably, the main circuit has the topological structure of following one：BUCK topological structures, BOOST topological structures, BUCK-BOOST topological structures, reverse exciting topological structure.

Another aspect according to the present utility model, provides a kind of control method for LED drive circuit, and the LED drives Dynamic circuit includes switching tube, the method includes：It obtains for characterizing the current detection signal for flowing through the switching tube；According to institute It states current detection signal and peak point current reference signal generates drive signal, the drive signal includes multiple switch period and tool There is the first duty ratio；Dim signal is obtained, the dim signal includes multiple dimming cycles and has the second duty ratio；And it adopts The conducting and disconnection that the switching tube is controlled with drive signal, to realize conversion of the DC input voitage to average anode current, Wherein, before the step of generating drive signal, the method further includes being compensated according to the second duty ratio of the dim signal The peak point current reference signal, to inhibit light modulation to shake.

Preferably, the dimming cycle of the dim signal is more than the switch periods of the drive signal, and, in each tune In photoperiod, the drive signal is provided when the dim signal is effective, stops providing institute when the dim signal is invalid State drive signal.

Preferably, reduce the peak point current reference signal under depth light modulation, to correspondingly reduce the driving letter Number switch periods.

Preferably, when the duty ratio of the dim signal is less than or equal to desired duty ratio, judge to dim shape in depth State.

Preferably, the expectation duty ratio is 20%.

Preferably, under depth light modulation, the duty ratio of the peak point current reference signal and the dim signal at Direct ratio.

Preferably, the peak point current reference signal is the difference signal of predetermined reference and the thermal compensation signal.

Preferably, under depth light modulation, the average anode current of the main circuit and the duty ratio of dim signal are in Nonlinear change.

Preferably, the calculation formula of the average anode current Iout of the main circuit is：

If Dcomp≤D≤1

If 0≤D<Dcomp (formula 2)

Wherein, Vref indicates that peak point current reference signal, Dcomp indicate it is expected that duty ratio, D indicate the second duty ratio, Rs Indicate that sampling resistor, K indicate constant.

Preferably, the step of compensating the peak point current reference signal include：Obtain the inversion signal of the dim signal； The inversion signal is divided and is filtered, signal is detected to generate duty ratio；And it is more than in duty ratio detection signal When predetermined value, the duty ratio is detected into the difference of signal and predetermined value as the thermal compensation signal.

Preferably, the step of compensating the peak point current reference signal include：Obtain the inversion signal of the dim signal； The first capacitance is charged and discharged under the control of the inversion signal, is accounted for be generated at the both ends of first capacitance Sky is than detection signal；When duty ratio detection signal is more than predetermined value, the duty ratio is detected into signal and predetermined value Difference is as the first thermal compensation signal；And the first thermal compensation signal is converted into the second thermal compensation signal.

Preferably, the predetermined value is the conducting voltage of diode.

Preferably, the step of the first thermal compensation signal being converted into the second thermal compensation signal include：Using operational amplifier by institute It states the first thermal compensation signal and is converted into the first current signal；First current signal is converted by the second current signal using current mirror； And the second current signal is converted by the second thermal compensation signal using resistance.

According to the LED drive circuit of the utility model embodiment, the peak is compensated according to the duty ratio of the dim signal It is worth current reference signal.Under depth light modulation, since the control circuit of LED drive circuit reduces the peak point current benchmark letter Number, to correspondingly reduce the switch periods of the drive signal.Since the quantity of the switch periods in each dimming cycle increases Add, therefore light modulation can be inhibited to shake.

Under depth light modulation, due to compensated peak current reference signal, average anode current and dim signal account for Sky is than being in nonlinear change.Compared to general PWM dimming curves, under same duty ratio, output current becomes smaller.Dimming depth can be with It is adjusted to deeper.And LED luminance variation effect is more preferable in dimming process.

Description of the drawings

By referring to the drawings to the description of the utility model embodiment, above-mentioned and other mesh of the utility model , feature and advantage will be apparent from, in the accompanying drawings：

Fig. 1 shows the circuit block diagram of existing LED drive circuit.

Fig. 2 shows the working waveform figures of the LED drive circuit of Fig. 1.

Fig. 3 shows the circuit block diagram of the LED drive circuit according to the utility model embodiment.

Fig. 4 shows the working waveform figure of the LED drive circuit of Fig. 3.

Fig. 5 shows the dimming curve under different light-modulating modes.

Fig. 6 shows that the peak current compensation module used in the LED drive circuit according to the utility model embodiment is a kind of The schematic circuit of example.

Fig. 7 shows that the peak current compensation module used in the LED drive circuit according to the utility model embodiment is another The schematic circuit of kind example.

Fig. 8 shows the flow chart of the control method for LED drive circuit according to the utility model embodiment.

Specific implementation mode

Hereinafter reference will be made to the drawings is more fully described the utility model.In various figures, identical element is using similar Reference numeral indicate.For the sake of clarity, the various pieces in attached drawing are not necessarily to scale.Furthermore, it is possible to be not shown Certain well known parts.

Many specific details of the utility model, such as the structure of device, material, size, place are described hereinafter Science and engineering skill and technology, to be more clearly understood that the utility model.But just as the skilled person will understand, The utility model can not be realized according to these specific details.

The utility model can be presented in a variety of manners, some of them example explained below.

Fig. 1 shows the circuit block diagram of existing LED drive circuit.The LED drive circuit is BUCK type topologys, and being used for will be defeated The DC input voitage Vin decompression transformations for entering end are the DC output voltage Vout of output end.

As shown in Figure 1, LED drive circuit 100 includes main circuit 110 and controller 120.Main circuit 110 includes switching tube M1, diode D1, inductance L1, sampling resistor Rs, output capacitance C1.Load resistance Rl in Fig. 1 indicates LED drive circuit 100 load, for example, the load is the lamp string of multiple LED compositions.

In the main circuit 110 of LED drive circuit 100, input voltage vin is applied between input terminal and ground.Diode D1, switching tube M1 and sampling resistor Rs are sequentially connected in series between input terminal and ground.The cathode of diode D1 is connected to input End, anode are connected to switching tube M1.Load resistance Rl and inductance L1 are connected in series between the cathode and anode of diode D1, defeated Go out capacitance C1 and load resistance Rl to be connected in parallel, output voltage Vout is generated at the both ends of output capacitance C1.Preferably, main circuit 110 further include the current-limiting resistance Rg for the control terminal for being connected to switching tube M1.

The feedback end and control terminal of the control circuit 120 of LED drive circuit 100 receive current sampling signal Is and tune respectively Optical signal PWM, output end provide drive signal Vg.For example, the feedback end of control circuit 120 is connected to switching tube M1 and sampling electricity The intermediate node for hindering Rs, to obtain current sampling signal Is.

Fig. 2 shows the working waveform figures of the LED drive circuit of Fig. 1.Illustrate that the LED of the embodiment drives below in conjunction with Fig. 1 and 2 The operation principle of dynamic circuit.

Control circuit 120 works for example, by using peak value comparison method mode, under the control of different dim signal PWM, The inductive current peak for flowing through switching tube M1 is maintained to immobilize according to current feedback signal Is.

The principle of PWM light modulations is switching tube M1 in each dimming cycle of Duty ratio control using dim signal PWM On-off times.Each dimming cycle of dim signal PWM includes valid period of such as high level and for example low level invalid Period.In the valid period of each dimming cycle, control circuit 120 provides the drive signal Vg changed according to switch periods. The invalid period of each dimming cycle, the drive signal Vg that control circuit 120 provides is always invalid.Dim signal PWM's accounts for Sky ratio D is the ratio of the valid period and dimming cycle of each dimming cycle.

When drive signal Vg is effective, switching tube M1 conductings, electric current is followed by load resistance Rl, inductance L1, switching tube M1 and sampling resistor Rs.DC input voitage Vin charges to inductance L1 and output capacitance C1, to be stored in inductance L1 Electric energy, and to load Rl power supplies.Inductive current IL substantial linears increase.Current sampling signal Is is for characterizing inductive current IL.When inductive current IL reaches scheduled peak value, drive signal Vg is changed into vain, and switching tube M1 is disconnected, inductance L1 via Diode D1 discharges the electric energy wherein stored, is powered to load resistance Rl using output capacitance C1, to maintain output voltage Vout and/or output current Iout.

In the control method, each dimming cycle of dim signal PWM includes the multiple switch period of drive signal Vg. By changing the duty ratio of dim signal PWM, the quantity of the switch periods in each dimming cycle is (that is, the switch of switching tube M1 Number) correspondingly change, to adjust average anode current, realize desired brightness.

The calculation formula of average anode current Iout is：

Wherein, Vref indicates that peak point current reference signal, D indicate that the duty ratio of dim signal PWM, Rs indicate sampling electricity Resistance.

According to formula (1), the peak point current reference signal Vref inside the controller 120 of LED drive circuit 100 is fixed When, using the on-off times of switching tube M1 in each dimming cycle of the Duty ratio control of dim signal PWM, so that it may to realize to straight The control of output current Iout is flowed, also, average anode current Iout and the duty ratio of dim signal PWM change linearly. With the reduction of the duty ratio of dim signal PWM, light modulation depth is increasing.In dimming process, the brightness change of LED is more next It is bigger, to the phenomenon that LED luminance shake occur.Therefore, when depth dims, dimming effect is deteriorated.

For example, after the duty ratio of dim signal PWM is less than 10%, dimming effect is deteriorated.It solves in the prior art The method of the technical problem is to limit the dimming scope of LED drive device, for example, the duty ratio of dim signal PWM is only allowed in Change between 10% to 100%.Correspondingly, maximum dimmer depth is 90%.However, largely to the limitation of dimming scope The application that PWM is dimmed is caused to be restricted.

Fig. 3 shows the circuit block diagram of the LED drive circuit according to the utility model embodiment.The LED drive circuit is BUCK type topologys, for the DC output voltage Vout by the DC input voitage Vin decompression transformations of input terminal for output end.

As shown in figure 3, LED drive circuit 200 includes main circuit 210 and controller 220.Main circuit 210 includes switching tube M1, diode D1, inductance L1, sampling resistor Rs, output capacitance C1.Load resistance Rl in figure 3 indicates LED drive circuit 200 load, for example, the load is the lamp string of multiple LED compositions.

The master of the main circuit 210 of LED drive circuit 200 and LED drive circuit according to prior art 100 shown in FIG. 1 Circuit 110 is identical, and this will not be detailed here.

The feedback end and control terminal of the control circuit 220 of LED drive circuit 200 receive current sampling signal Is and tune respectively Optical signal PWM, output end provide drive signal Vg.For example, the feedback end of control circuit 220 is connected to switching tube M1 and sampling electricity The intermediate node for hindering Rs, to obtain current sampling signal Is.

Further, which includes peak current compensation module 221.The peak current compensation module 221 is used In the duty ratio size of detection dim signal PWM, to the peak value of inductive current IL of the control under different duty.In depth Light modulation is lower to carry out inductive current peak compensation.In this embodiment, the duty ratio for the PWM that depth light modulation for example refers to dim signal is big In equal to zero, and it is less than or equal to 20%, duty ratio is smaller, and compensation rate is bigger.Due to compensating inductive current IL under being dimmed in depth Peak, in the case of same duty cycle, the on-off times of switching tube M1 increase.The raising of the on-off times can effectively change It is apt to the dimming state in the case where depth dims, light modulation depth is further increased, so as to improve LED luminance jitter phenomenon in dimming process.

Fig. 4 shows the working waveform figure of the LED drive circuit of Fig. 3.Illustrate that the LED of the embodiment drives below in conjunction with Fig. 3 and 4 The operation principle of dynamic circuit.

Control circuit 220 works for example, by using peak value comparison method mode, under the control of different dim signal PWM, The inductive current peak for flowing through switching tube M1 is maintained to immobilize according to current feedback signal Is.

The principle of PWM light modulations is switching tube M1 in each dimming cycle of Duty ratio control using dim signal PWM On-off times.Each dimming cycle of dim signal PWM includes valid period of such as high level and for example low level invalid Period.In the valid period of each dimming cycle, control circuit 220 provides the drive signal Vg changed according to switch periods. The invalid period of each dimming cycle, the drive signal Vg that control circuit 220 provides is always invalid.Dim signal PWM's accounts for Sky ratio D is the ratio of the valid period and dimming cycle of each dimming cycle.

When drive signal Vg is effective, switching tube M1 conductings, electric current is followed by load resistance Rl, inductance L1, switching tube M1 and sampling resistor Rs.DC input voitage Vin charges to inductance L1 and output capacitance C1, to be stored in inductance L1 Electric energy, and to load Rl power supplies.Inductive current IL substantial linears increase.Current sampling signal Is is for characterizing inductive current IL.When inductive current IL reaches scheduled peak value, drive signal Vg is changed into vain, and switching tube M1 is disconnected, inductance L1 via Diode D1 discharges the electric energy wherein stored, is powered to load resistance Rl using output capacitance C1, to maintain output voltage Vout and/or output current Iout.

In the control method, each dimming cycle of dim signal PWM includes the multiple switch period of drive signal Vg. By changing the duty ratio of dim signal PWM, the quantity of the switch periods in each dimming cycle is (that is, the switch of switching tube M1 Number) correspondingly change, to adjust average anode current, realize desired brightness.

The calculation formula of average anode current Iout is：

If Dcomp≤D≤1

If 0≤D<Dcomp (formula 2)

Wherein, Vref indicates that peak point current reference signal, Dcomp indicate it is expected that duty ratio, D indicate dim signal PWM's Duty ratio, Rs indicate that sampling resistor, K indicate constant.

According to formula (2), when the duty ratio D of dim signal PWM is more than or equal to desired duty ratio Dcomp, LED driving electricity Peak point current reference signal Vref inside the controller 220 on road 200 is fixed, and the Duty ratio control using dim signal PWM is every The on-off times of switching tube M1 in a dimming cycle, so that it may to realize the control to average anode current Iout, also, the direct current Output current Iout and the duty ratio of dim signal PWM change linearly.

When the duty ratio D of dim signal PWM is less than desired duty ratio Dcomp, the controller 220 of LED drive circuit 200 Internal peak point current reference signal subtracts thermal compensation signal, to obtain difference signal：Vref '=Vref-K* (Dcomp-D).With That light modulation depth is increasing, the duty ratio D of dim signal PWM reduces.Difference signal Vref ' with the reduction of duty ratio D and Reduce, therefore, peak point current reference signal is directly proportional to the duty ratio D of dim signal.Week is dimmed in each of dim signal PWM Interim, the switch periods of switching tube M1 reduce and on-off times correspondingly increase.Average anode current Iout and dim signal The duty ratio of PWM is in nonlinear change.

Fig. 5 shows the dimming curve under different light-modulating modes, wherein being shown respectively under PWM light modulations according to the utility model The LED drive circuit of embodiment uses the dimming curve of inductive current peak compensation, and LED drivings electricity according to prior art Road does not use the dimming curve of inductive current peak compensation.From fig. 5, it is seen that the average anode current Iout after compensation Variation no longer with duty ratio present linear change.

Using the LED drive circuit of the utility model embodiment, by controlling the inductive current peak under different duty, And then output current size is controlled, to realize brightness adjustment control.Under identical duty ratio, average anode current becomes smaller.Therefore, The light modulation depth of the LED drive circuit can be adjusted to deeper.The LED drive circuit allow dimming scope can 0% to Change between 100%.Further, since when depth dims, each dimming cycle of dim signal PWM can include driving More switch periods of signal Vg, therefore, the brightness change of LED is stablized in dimming process, to overcome dimming process In brightness jitter the problem of.

Fig. 6 shows that the peak current compensation module used in the LED drive circuit according to the utility model embodiment is a kind of The schematic circuit of example.In this example, peak current compensation module 2211 includes transistor Q1, diode D11, resistance R11 to R15.

As shown in fig. 6, resistance R11 and transistor Q1 are connected in series between feeder ear VCC and ground.The control of transistor Q1 End connection resistance R12, dim signal PWM is received via resistance R12.The intermediate node of resistance R11 and transistor Q1 generate tune The inversion signal of optical signal PWM.Then, which is divided via resistance R13 and the R14 potential-divider network formed, so It is filtered by by capacitance C11, the detection letter of the duty ratio for characterizing dim signal PWM is generated at the both ends of capacitance C11 Number A.The duty ratio of dim signal PWM is bigger, and the voltage of detection signal A is lower.

Diode D11 and resistance R15 are connected in series between the hot end of capacitance C11 and output end B.As light modulation is believed The voltage of the reduction of the duty ratio of number PWM, detection signal A increases, until being more than the forward conduction voltage of diode D11, two poles Pipe D11 conductings, thus in output end B, using the difference of the conducting voltage of the detection signal A and diode D11 as benefit Repay signal Vcomp.By the numerical value for selecting resistance R13 and R14 in potential-divider network so that thermal compensation signal Vcomp=K* (Dcomp-D)。

Further, peak point current reference signal Vref is subtracted compensation letter by the control circuit 220 of LED drive circuit 200 Number, obtain difference signal Vref '=Vref-K* (Dcomp-D).Under depth light modulation, which accounts for according to dim signal PWM's Sky compares and changes, to substitute fixed peak point current reference signal Vref.

Under depth light modulation, LED drive circuit 200 compensates inductive current peak according to the duty ratio of dim signal PWM, from And the on-off times of switching tube in each dimming cycle are controlled, to improve dimming effect.

Fig. 7 shows that the peak current compensation module used in the LED drive circuit according to the utility model embodiment is another The schematic circuit of kind example.In this example, peak current compensation module 2212 includes switch S1, constant-current source I11, operation Amplifier A11, current mirror K11, transistor M11, diode D11, resistance R11 to R15.

Switch S11 open and closes under the control of the inversion signal of dim signal PWM.Constant-current source I11 is via switch S1 It is connected to capacitance C11, in the case of switch S11 is closed, charge to capacitance C11.Resistance R11 and capacitance C11 is simultaneously Connection connection, to the charge that in the case of switch S11 is disconnected, release capacitance C11 stores.Use is generated at the both ends of capacitance C11 In the detection signal A of the duty ratio of characterization dim signal PWM.Since the control signal of switch S11 is the reverse phase of dim signal PWM Signal, therefore, the duty ratio of dim signal PWM are bigger, and the voltage of detection signal A is lower.

Diode D11 and resistance R12 are connected in series between the hot end and ground of capacitance C11.With dim signal PWM Duty ratio reduction, the voltage of detection signal A increases, until being more than the forward conduction voltage of diode D11, diode D11 Conducting, to obtain the first thermal compensation signal B in the intermediate node of diode D11 and resistance R12.The first thermal compensation signal B is The difference of the conducting voltage of the detection signal A and diode D11.

In this embodiment, signal conversion module includes transistor M11, resistance R13 to R15, operational amplifier A 11 and electricity Flow mirror K11.First thermal compensation signal B is converted into the first current signal by signal conversion module using operational amplifier M11, using electricity First current signal is converted into the second current signal by stream mirror K11, and the second current signal is converted into the using resistance R14 Two thermal compensation signal Vcomp.

In signal conversion module, transistor M11 and resistance R13 are connected in series between the input terminal and ground of current mirror K11, Resistance R14 and R15 are connected in series between the output end and ground of current mirror K11.The in-phase input end of operational amplifier A 11 receives First thermal compensation signal B, inverting input are connected to the intermediate node of transistor M11 and resistance R13, and output end is connected to transistor The control terminal of M11.First thermal compensation signal B is converted into electric current letter via operational amplifier A 11 and current mirror K11, from voltage signal Number.

In the output end of current mirror K11, the voltage drop i.e. second thermal compensation signal Vcomp at the both ends resistance R14.It is permanent by selecting The numerical value of stream source I11, capacitance C11 and resistance R11, operational amplifier A 11, current mirror K11, resistance R13 to R14 so that compensation Signal Vcomp=K* (Dcomp-D).

Further, peak point current reference signal Vref is subtracted compensation letter by the control circuit 220 of LED drive circuit 200 Number, obtain difference signal Vref '=Vref-K* (Dcomp-D).Under depth light modulation, which accounts for according to dim signal PWM's Sky compares and changes, to substitute fixed peak point current reference signal Vref.

Under depth light modulation, LED drive circuit 200 compensates inductive current peak according to the duty ratio of dim signal PWM, from And the on-off times of switching tube in each dimming cycle are controlled, to improve dimming effect.

Preferably, most of circuit element of the peak current compensation module 2212 can be integrated in one single chip, only The only peripheral cell of resistance R11 and R15 and capacitance C11 as the chip.

In the above-described embodiment, the main circuit for describing LED drive circuit is the embodiment of BUCK topologys.However, this Utility model is without being limited thereto, but can be applied to the topological structure under any Peak Current-Mode Controlled Circuit, for example, BUCK is topological Structure, BOOST topological structures, BUCK-BOOST topological structures, reverse exciting topological structure.

Fig. 8 shows the flow chart of the control method for LED drive circuit according to the utility model embodiment.This method Such as LED drive circuit 200 shown in Fig. 3, the drive signal Vg for generating switching tube M1.

In step S01, the current detection signal for characterizing the electric current for flowing through the switching tube is obtained.

In step S02, dim signal and peak point current reference signal are obtained.

In step S03, drive signal, the drive are generated according to the current detection signal and peak point current reference signal Dynamic signal includes the multiple switch period and there is the first duty ratio, the dim signal to include multiple dimming cycles and have second Duty ratio.

In the method, the dimming cycle for stating dim signal is more than the switch periods of the drive signal, and, each In dimming cycle, the drive signal is provided when the dim signal is effective, stops providing when the dim signal is invalid The drive signal.

The peak point current reference signal is compensated according to the second duty ratio of the dim signal, to inhibit light modulation to tremble It is dynamic.Under depth light modulation, the duty ratio of the dim signal is less than or equal to desired duty ratio, it is expected that duty ratio is, for example, 20%. Under depth light modulation, the peak point current reference signal is directly proportional to the duty ratio of the dim signal, with dim signal Duty ratio reduces, and correspondingly reduces the peak point current reference signal, to correspondingly reduce the switch week of the drive signal Phase.

In the method, peak point current reference signal is the difference signal of predetermined reference and the thermal compensation signal.

In an example, the step of compensating the peak point current reference signal include：Obtain the anti-of the dim signal Phase signals；The inversion signal is divided and is filtered, signal is detected to generate duty ratio；And it detects and believes in the duty ratio When number being more than predetermined value, the duty ratio is detected into the difference of signal and predetermined value as the thermal compensation signal.

In another example, the step of compensating the peak point current reference signal include：Obtain the dim signal Inversion signal；The first capacitance is charged and discharged under the control of the inversion signal, in first capacitance Both ends generate duty ratio and detect signal；When duty ratio detection signal is more than predetermined value, the duty ratio is detected into signal Difference with predetermined value is as the first thermal compensation signal；And the first thermal compensation signal is converted into the second thermal compensation signal.

Further, the step of the first thermal compensation signal being converted into the second thermal compensation signal include：It will using operational amplifier First thermal compensation signal is converted into the first current signal；First current signal is converted by the second electric current letter using current mirror Number；And the second current signal is converted by the second thermal compensation signal using resistance.Above-mentioned predetermined value is the electric conduction of diode Pressure.

In step S04, the conducting and disconnection of the switching tube are controlled using drive signal, to realize DC input voitage To the conversion of average anode current,

It should be noted that herein, relational terms such as first and second and the like are used merely to a reality Body or operation are distinguished with another entity or operation, are deposited without necessarily requiring or implying between these entities or operation In any actual relationship or order or sequence.Moreover, the terms "include", "comprise" or its any other variant are intended to Non-exclusive inclusion, so that the process, method, article or equipment including a series of elements is not only wanted including those Element, but also include other elements that are not explicitly listed, or further include for this process, method, article or equipment Intrinsic element.In the absence of more restrictions, the element limited by sentence "including a ...", it is not excluded that There is also other identical elements in process, method, article or equipment including the element.

It is as described above according to the embodiments of the present invention, these embodiments there is no all details of detailed descriptionthe, The specific embodiment that the utility model is only described is not limited yet.Obviously, as described above, many modification and change can be made Change.These embodiments are chosen and specifically described to this specification, is in order to preferably explain the principles of the present invention and actually to answer With to enable skilled artisan to utilize the utility model and repairing on the basis of the utility model well Change use.The utility model is limited only by the claims and their full scope and equivalents.

Claims (15)

1. a kind of LED drive circuit, which is characterized in that including：

Main circuit, the main circuit include switching tube, realize DC input voitage to direct current using the conducting and disconnection of switching tube The conversion of output current；And

Control circuit is connected with the main circuit, for providing drive signal to the switching tube, to control the switching tube Conducting state,

Wherein, the control circuit obtains current detection signal from the main circuit, and according to the current detection signal and Peak point current reference signal executes peak value comparison method so that the switching tube is in each switch periods of the drive signal Switched conductive state, the drive signal have the first duty ratio,

The control circuit receives dim signal, and the output of the drive signal is controlled according to the dim signal, described Dim signal has the second duty ratio,

The control circuit includes peak current compensation module, and the peak value is compensated according to the second duty ratio of the dim signal Current reference signal, to inhibit light modulation to shake.

2. LED drive circuit according to claim 1, which is characterized in that the dimming cycle of the dim signal is more than institute The switch periods of drive signal are stated, and, in each dimming cycle, when the dim signal is effective, the control circuit The drive signal is provided, when the dim signal is invalid, the control circuit stops providing the drive signal.

3. LED drive circuit according to claim 1, which is characterized in that the control circuit reduces under depth light modulation The peak point current reference signal, to correspondingly reduce the switch periods of the drive signal.

4. LED drive circuit according to claim 3, which is characterized in that be less than in the duty ratio of the dim signal etc. When desired duty ratio, judge to be in depth dimming state.

5. LED drive circuit according to claim 4, which is characterized in that under depth light modulation, the peak point current Reference signal is directly proportional to the duty ratio of the dim signal.

6. LED drive circuit according to claim 5, which is characterized in that the input terminal of the peak current compensation module Receive the dim signal, output end provides thermal compensation signal, the peak point current reference signal be predetermined reference with it is described The difference signal of thermal compensation signal.

7. LED drive circuit according to claim 6, which is characterized in that under depth light modulation, the main circuit The duty ratio of average anode current and dim signal is in nonlinear change.

8. LED drive circuit according to claim 7, which is characterized in that the average anode current Iout of the main circuit Calculation formula be：

If Dcomp≤D≤1

If 0≤D<Dcomp

Wherein, Vref indicates that peak point current reference signal, Dcomp indicate it is expected that duty ratio, D indicate that the second duty ratio, Rs indicate Sampling resistor, K indicate constant.

9. LED drive circuit according to claim 6, which is characterized in that the peak current compensation module includes：

The first resistor and transistor being connected in series between feeder ear and ground, between the first resistor and the transistor First node generate the inversion signal of the dim signal；

Second resistance is connected between the input terminal and the control terminal of the transistor；

Potential-divider network is connected between the first node and ground, for being divided to the inversion signal, the potential-divider network tool There is second node；

First capacitance is connected between the second node and ground, for being filtered to the inversion signal, is accounted for generate Sky is than detection signal；And

The anode of diode, the diode is connected to the second node, and cathode is connected to the output end, for providing State thermal compensation signal.

10. LED drive circuit according to claim 9, which is characterized in that the potential-divider network includes be connected in series with Three resistance and the 4th resistance, the second node are the intermediate node of the 3rd resistor and the 4th resistance.

11. LED drive circuit according to claim 9, which is characterized in that further include：It is connected in series in the diode The 5th resistance between the output end.

12. LED drive circuit according to claim 6, which is characterized in that the peak current compensation module includes：

The first constant-current source, first switch and the first capacitance being connected in series between feeder ear and ground, the first switch is in institute It states and is connected and disconnects under the control of the inversion signal of dim signal, when the first switch is connected, first constant-current source pair First capacitor charging, the first node between the first switch and first capacitance generate duty ratio detection letter Number；

First resistor is connected in parallel with first capacitance, and when the first switch disconnects, first capacitance is via described First resistor is discharged；

The diode and second resistance being connected in series between the first node and ground, in the diode and second electricity Second node between resistance generates the first thermal compensation signal；And

Signal conversion module is connected between the second node and the output end, for the first thermal compensation signal to be converted into Second thermal compensation signal.

13. LED drive circuit according to claim 12, which is characterized in that the signal conversion module includes：

Current mirror；

The first transistor and 3rd resistor being connected in series between the input terminal of current mirror and ground；

The 4th resistance and the 5th resistance being connected in series between the output end of current mirror and ground；And

Operational amplifier, the in-phase input end of the operational amplifier is connected to the second node to be believed with receiving the compensation Number, inverting input is connected to the third node between the first transistor and the 3rd resistor,

Wherein, the both ends of the 4th resistance are connected to the output end, to provide the thermal compensation signal.

14. LED drive circuit according to claim 1, which is characterized in that the main circuit has the topology of following one Structure：BUCK topological structures, BOOST topological structures, BUCK-BOOST topological structures, reverse exciting topological structure.

15. a kind of LED drive circuit, which is characterized in that including：

Main circuit, the main circuit include switching tube, realize DC input voitage to direct current using the conducting and disconnection of switching tube The conversion of output current；And

Control circuit is connected with the main circuit, for providing drive signal to the switching tube, to control the switching tube Conducting state,

Wherein, the control circuit obtains current detection signal from the main circuit, and according to the current detection signal and Peak point current reference signal executes peak value comparison method so that the switching tube is in each switch periods of the drive signal Switched conductive state, the drive signal have the first duty ratio,

The control circuit receives dim signal, and the output of the drive signal is controlled according to the dim signal, described Dim signal has the second duty ratio so that the average anode current Iout of the main circuit is：

If Dcomp≤D≤1

If 0≤D<Dcomp

Wherein, Vref indicates that peak point current reference signal, Dcomp indicate it is expected that duty ratio, D indicate that the second duty ratio, Rs indicate Sampling resistor, K indicate constant.