CN101489342B - LED driver circuit and driving method thereof - Google Patents

Abstract

The present invention discloses an LED driving circuit and a driving method thereof, wherein the LED driving circuit comprises a sampling and threshold setting module, a comparing module, a switching control module, a driving module and a switching module. The sampling and threshold setting module samples the two-end voltages Vs of peripheral LED circuit and simultaneously generates a threshold setting signal Vt. The comparing module compares Vs with Vt. A comparing signal Vc is output to the switching control module. The switching control module outputs a signal S3 to the driving module. The driving module generates signals PWM, PWM1 and S1. The signal PWM1 is fed back to the sampling and threshold setting module. The signal S1 is fed back to the switching control module. The signal PWM is output to the switching module. The switching module controls the peripheral LED circuit. The invention reduces the average output current when the voltage difference between the output voltage Vin of LED driving circuit and the rated output voltage of LED load is small. The invention settles the problems of LED service lifetime effect caused by overlarge current and LED lamp twinkling caused by current variation.

Description

Led drive circuit and driving method thereof

Technical field

The present invention relates to the led drive circuit technology, relate in particular to the current-limiting protection technology of the led drive circuit of the ring control model that stagnates.

Background technology

Led drive circuit, particularly high-power LED drive circuit extensively adopt the ring control model that stagnates, and its control loop is simple, need not slope compensation and frequency compensation, and required peripheral component is few, makes things convenient for the client to use.

At present, the part-structure of the led drive circuit of the stagnant ring control model that generally adopts is as shown in Figure 1, comprises sampling and threshold setting module 10, comparison module 11, driver module 12 and switch module 13, wherein:

Said sampling and the Vin port of threshold setting module 10 are connected the sampling resistor Rsense two ends of external led circuit with the CS port; The voltage of sampling Rsense; And be voltage sampling signal Vs with the voltage amplification on the Rsense through amplifying circuit; Sampling simultaneously and the threshold setting module 10 inner setting threshold signal Vt that produce, voltage sampling signal Vs and setting threshold signal Vt input comparison module 11 compare, and the Vin port of said sampling and threshold setting module 10 inserts external input voltage; The PWM1 port connects driver module 12, sampling and threshold setting module ground connection;

Said comparison module 11 produces comparison signal Vc, exports to driver module 12;

Said driver module 12 produces signal PWM and signal PWM1, signal PWM input switch module 13, and signal PWM1 feeds back to sampling and threshold setting module 10, thereby changes voltage sampling signal Vs or the setting threshold signal Vt that samples with threshold setting module 10;

The output port SW of said switch module 13 controls the break-make of external led circuit, switch module 13 ground connection.

The operation principle of led drive circuit shown in Figure 1 is:

(1) when the rated output voltage at the LED of led drive circuit input voltage vin and external led circuit load two ends differs big; Led drive circuit and external led circuit initially power on; The Vs signal of the sampling of led drive circuit and threshold setting module 11 outputs is less than the value of signal Vt, the SW port output low level of the switch module 13 of led drive circuit, and input voltage vin is through the sampling resistor Rsense of external led circuit; The LED load; Inductance L 1, switch module 13 is to the branch road conducting on ground, and this branch road has electric current I _L1Occur, because inductance L 1 is an energy-storage travelling wave tube, I _L1Be the electric current that increases gradually from small to large, when voltage sampling signal Vs equals setting threshold signal Vt, comparison module 11 upsets; The output signal PWM upset of driver module 12; Switch module 13 turn-offs, and the output signal PWM1 of driver module 12 feeds back to sampling and threshold setting module 10 simultaneously, and voltage sampling signal Vs moment is increased or setting threshold signal Vt is reduced to minimum value (the general time stagnant voltage that stagnates ring control led drive circuit is about 30%) by maximum moment; Vs signal moment increases or Vt value moment reduces to be reacted to external led circuit; Be about to inductance L 1 electric current and change to minimum threshold Imin by max-thresholds Imax, as shown in Figure 3, switch module 13 closes has no progeny; The electric energy that inductance L 1 stores still has the electric current I that reduces gradually through Schottky diode D1 afterflow _L1Through the loop of inductance L 1, Schottky diode D1, sampling resistor Rsense and LED load composition, along with the consumption and the discharging current I of L1 energy storage _L1Reduce gradually, when voltage sampling signal Vs was reduced to setting threshold signal Vt, comparison module 11 overturn once more; The output signal PWM of driver module 12 overturns once more, switch module 13 conductings, and simultaneously the PWM1 signal reduces voltage sampling signal Vs moment or setting threshold signal Vt is increased to maximum by minimum value moment; Vs signal moment reduce or Vt signal moment augmenting response to external led circuit; The compare threshold that is about to inductance L 1 electric current changes to max-thresholds Imax by minimum threshold Imin, and after after a while, it is stable that output waveform reaches; Outputting current steadily; Led drive circuit system Automatic Cycle said process is realized the stagnant ring of LED load is driven, inductive current I when the rated output voltage for input voltage vin and the LED load two ends of external led circuit shown in Figure 3 differs greatly _L1Waveform can be seen from figure, and the LED load output average current Iout1 of external led circuit is the mean value of maximum current threshold value Imax and minimum current threshold value Imin, that is:

$\mathrm{Iout}1=\frac{I\max +I\mathrm{<figure-callout\; id="2"\; label="min"\; filenames="H2009100962180E00042.png"\; state="\{\{state\}\}">min</figure-callout>}}{2}$

(2) differ hour when the rated output voltage at the LED of led drive circuit input voltage vin and external led circuit load two ends; Led drive circuit and external led circuit initially power on; The voltage sampling signal Vs of the sampling of led drive circuit and threshold setting module 11 outputs is less than setting threshold signal Vt, the SW port output low level of the switch module 13 of led drive circuit, and input voltage vin is through the sampling resistor Rsense of external led circuit; The LED load; Inductance L 1, switch module 13 is to the branch road conducting on ground, and this branch road has electric current I _L2Occur, because inductance L 1 is an energy-storage travelling wave tube, I _L2Be an electric current that increases gradually from small to large, thus the time input voltage vin and external led circuit the rated output voltage at middle LED load two ends approaching, I _L2Can keep constant when electric current increases to certain value, can not reach lowest high-current value, this moment, voltage sampling signal Vs was lower than setting threshold signal Vt all the time, and comparison module 11 does not overturn, and switch module 12 is in conducting state always, and the output of SW is low all the time, at this moment I _L2Current waveform is as shown in Figure 4, from figure, can see, the mean value of average current Iout2 greater than maximum current threshold value and minimum current threshold value is exported in the LED load in the external led circuit, and can be near maximum current threshold value Imax.

Can know through above-mentioned analysis; The led drive circuit shortcoming of Fig. 1, stagnant ring control model shown in Figure 2 is: when the rated output voltage at the LED of led drive circuit input voltage vin and external led circuit load two ends differs hour; Inductive current can not reach external led circuit inductance maximum current Imax; Switch module is in opening state always; And in certain voltage pressure differential range, the LED load output current of external led circuit can be higher than the average current value (lowest high-current value of the general ring drive controlling that stagnates is bigger by about 15% than the average current of setting) of setting near lowest high-current value; Under this user mode, the electric current in the LED load will be bigger by about 15% than rated operational current.Practical test result has also confirmed this shortcoming: the led drive circuit that adopts hysteresis control method thereof at present; Generally at the LED lamp (about three LEDs pressure drop 9.6V) that drives three polyphones under 10～12V input voltage; Output current had from 1.15 times of electric currents setting current value and is reduced to the process appearance of setting current value when voltage was changed by 10V～12V; The variation of the LED load output current of external led circuit makes the electric current of LED load be not easy control; Influence luminous stability, can have a strong impact on the life-span of LED when simultaneously the output current of led drive circuit surpasses the rated current of LED.

Summary of the invention

The present invention is intended to solve the deficiency of prior art; Provide under a kind of stagnant ring control model; When the rated output voltage at the input voltage vin of led drive circuit and the LED load two ends in the external led circuit differs hour, has the led drive circuit of current-limiting protection effect.

The present invention simultaneously also provides the driving method of led drive circuit.

Led drive circuit comprises sampling and threshold setting module, comparison module, shutoff control module, driver module and switch module:

Said sampling and the Vin port of threshold setting module are connected the two ends of the sampling resistor Rsense of external led circuit with the CS port; The voltage of sampling Rsense; And be voltage sampling signal Vs with the amplifying circuit of threshold setting module with the voltage amplification on the Rsense through sampling; Sampling simultaneously produces setting threshold signal Vt with the threshold setting inside modules, and voltage sampling signal Vs and setting threshold signal Vt input comparison module compare, and the Vin port of said sampling and threshold setting module inserts external input voltage; The PWM1 port connects driver module, sampling and threshold setting module ground connection;

Said comparison module produces comparison signal Vc input and turn-offs control module;

Said shutoff control module is accepted the feedback of driver module simultaneously, produces signal S3 input driver module;

Said driver module produces signal PWM, signal PWM1 and signal S1; Signal PWM input switch module; Signal PWM1 feeds back to sampling and threshold setting module, changes the voltage sampling signal Vs or the setting threshold signal Vt of sampling and threshold setting module, and signal S1 feeds back to the shutoff control module;

The output port SW of said switch module controls the break-make of external led circuit, switch module ground connection.

When the LED of led drive circuit input voltage vin and external led circuit load two ends rated output voltage differs hour, the high level time of signal S1 that detects driver module output when the shutoff control module of led drive circuit is when turn-offing the setting-up time t1 of control module, and the output signal S3 that turn-offs control module is after driver module strengthens; The pwm signal step-down of control and driving module output, switch module turn-offs, and turn-offs control module signal S3 is delayed time t2 after the time; Signal S3 overturns once more, and signal S3 is after driver module drives enhancing, and the output signal PWM of control and driving module uprises; The switch module conducting; SW port output low level, pwm signal is for continuing t1 time high level, and the duration is the low level fixed pulse width signal of t2; After after a while, the led drive circuit output waveform reaches stable.

As above the driving method of led drive circuit is:

(1) differs hour when the LED of led drive circuit input voltage vin and external led circuit load two ends rated output voltage; Led drive circuit and external led circuit initially power on; The voltage sampling signal Vs of the sampling of led drive circuit and threshold setting module output is less than setting threshold signal Vt, the switch module SW port output low level of led drive circuit, and input voltage vin is through the sampling resistor Rsense of external led circuit; The LED load; Inductance L 1, switch module is to the branch road conducting on ground, and this branch road has electric current I _L3Occur, because inductance L 1 is an energy-storage travelling wave tube, I _L3Be the electric current that increases gradually from small to large, the high level lasting time of S1 signal that detects driver module output when the shutoff control module of led drive circuit is when turn-offing the setting-up time t1 of control module, and the signal S3 that turn-offs control module is after driver module strengthens; The pwm signal step-down of control and driving module output, switch module turn-offs, and turn-offs control module with S3 signal lag t2 after the time; Signal S3 overturns once more, and S3 is after driver module drives enhancing, and the output pwm signal of control and driving module uprises; The switch module conducting, SW port output low level, pwm signal is for continuing t1 time high level; Duration is the low level fixed pulse width signal of t2; After after a while, the led drive circuit output waveform reaches stable, LED load outputting current steadily; Led drive circuit Automatic Cycle said process realizes that led drive circuit drives the stagnant ring of external led circuit.

(2) when the LED of led drive circuit input voltage vin and external led circuit load two ends rated output voltage differs big; Be under the normal operating conditions, led drive circuit and external led circuit initially power on, and the voltage sampling signal Vs of the sampling of led drive circuit and the output of threshold setting module is less than setting threshold signal Vt; The SW port output low level of the switch module of led drive circuit; Input voltage vin is through the sampling resistor Rsense of external led circuit, LED load, inductance L 1; Switch module is to the branch road conducting on ground, and this branch road has electric current I _L4Occur, because inductance L 1 is an energy-storage travelling wave tube, I _L4Be the electric current that increases gradually from small to large, the service time of switch module is less than the time t1 of the setting of turn-offing control module, therefore; The S1 signal of driver module output can not cause the upset of the S3 signal that turn-offs control module output; Only by the output voltage V c decision of comparison module, when voltage sampling signal Vs increased to setting threshold signal Vt, output voltage V c's S3 signal of comparison module overturn; Then turn-off the output signal S3 upset of control module; Thereby cause the output signal PWM upset of driver module, switch module turn-offs, and the output signal PWM1 of driver module increases sampled voltage Vs moment perhaps the Vt signal is reduced to minimum value by maximum moment simultaneously; The electric energy that inductance L 1 stores still has the electric current I that reduces gradually through Schottky diode D1 afterflow _L1Through the loop of inductance L 1, Schottky diode D1, sampling resistor Rsense and LED load composition, along with the consumption and the discharging current I of L1 energy storage _L4Reduce gradually, when voltage sampling signal Vs was reduced to setting threshold signal Vt, comparison module overturn once more; Driver module output signal PWM overturns once more; The switch module conducting, simultaneously the PWM1 signal reduces voltage sampling signal Vs moment or setting threshold signal Vt is increased to maximum by minimum value moment, Vs signal moment reduce or Vt signal moment augmenting response to external circuit; The compare threshold that is about to inductance L 1 electric current changes to max-thresholds Imax by minimum threshold Imin; After after a while, it is stable that output waveform reaches, outputting current steadily; Led drive circuit Automatic Cycle said process realizes that led drive circuit drives the stagnant ring of external led circuit.

Beneficial effect of the present invention is: the stagnant ring led drive circuit that adds current-limiting protection circuit input voltage vin with the LED load two ends rated output voltage pressure reduction of external led circuit hour; The switch module of led drive circuit has been avoided the phenomenon of conducting always; Promptly fixedly service time t1 is arranged in each cycle; Fixing turn-off time t2, thus limited the size of average output current, through t1 and t2 time are set; Make average output current be far smaller than max-thresholds electric current I max, thereby solved the excessive problem of electric current the influence in LED life-span and the LED lamp flicker that the electric current variation brings under certain workplace.

Description of drawings

Fig. 1 stagnates to encircle the led drive circuit part-structure figure of control model at present.

Fig. 2 stagnates to encircle the circuit diagram of the led drive circuit of control model with external led circuit at present.

Fig. 3 flows through the actual current oscillogram of inductance when pressure reduction is big for the led drive circuit of the ring control model that stagnates at present.

Fig. 4 hour flows through the actual current oscillogram of inductance at pressure reduction for the led drive circuit of the ring control model that stagnates at present.

Fig. 5 is led drive circuit part-structure figure of the present invention.

Fig. 6 is the circuit diagram A of led drive circuit of the present invention with external led circuit.

Fig. 7 is the circuit diagram B of led drive circuit of the present invention with external led circuit.

Fig. 8 turn-offs the circuit diagram of control module for led drive circuit of the present invention.

Fig. 9 is the signal waveforms of led drive circuit of the present invention.

Embodiment

Below in conjunction with accompanying drawing content of the present invention is further specified.

As shown in Figure 5, led drive circuit comprises sampling and threshold setting module 10, comparison module 11, shutoff control module 14, driver module 12 and switch module 13:

Said sampling and the Vin port of threshold setting module 10 are connected the two ends of the sampling resistor Rsense of external led circuit with the CS port; The voltage of sampling Rsense; And be voltage sampling signal Vs with the voltage amplification on the Rsense through amplifying circuit; Sampling simultaneously and the threshold setting module 10 inner setting threshold signal Vt that produce, voltage sampling signal Vs and setting threshold signal Vt input comparison module 11 compare, and the Vin port of said sampling and threshold setting module 10 inserts external input voltage; The PWM1 port connects driver module 12, sampling and threshold setting module ground connection;

Said comparison module 11 produces comparison signal Vc, exports to and turn-offs control module 14;

Said shutoff control module 14 is accepted the feedback of driver module 12 simultaneously, and produces signal S3 input driver module 12;

Said driver module 12 produces signal PWM, signal PWM1 and signal S1; Signal PWM input switch module 13; Signal PWM1 feeds back to sampling and threshold setting module 10; Thereby change the voltage sampling signal Vs or the setting threshold signal Vt of sampling and threshold setting module, signal S1 feeds back to and turn-offs control module 14;

The output port SW of said switch module 13 controls the break-make of external led circuit, switch module ground connection.

Like Fig. 5, Fig. 6, shown in Figure 7, described external led circuit comprises sampling resistor Rsense, LED load, inductance L 1 and the Schottky diode D1 of serial connection.

Fig. 6 is the circuit diagram of led drive circuit shown in Figure 5:

Wherein, the amplifying circuit of said sampling and threshold setting module 10 comprises amplifier A1, metal-oxide-semiconductor M3, metal-oxide-semiconductor M2, resistance R 1, resistance R 2, resistance R 3, and described Vin port connects the negative input end of comparator A1 through resistance R 1; The CS port connects the positive input terminal of comparator A1; The output of comparator A1 connects the grid of M3, and the source electrode of M3 is connected the other end and the resistance R 2 of resistance R 1 respectively with draining, resistance R 2, R3 series connection; The other end ground connection of R3; The drain electrode of M2 connects between resistance R 2 and the R3, and the source electrode of M2 connects resistance R 3 earth terminals, and the grid of M2 connects driver module 12;

Wherein, That said comparison module 11 adopts is comparator A2; The positive input terminal of comparator A2 connects voltage sampling signal Vs, and the negative input end of comparator A2 connects the setting threshold signal Vt of sampling and 10 outputs of threshold setting module, and the output of comparator A2 produces comparison signal Vc;

Wherein, said switch module adopts switching tube M1, and the grid of M1 connects the driver DR1 of driver module, the source ground of M1, and the drain electrode of M1 is as the SW output of led drive circuit;

Wherein, be illustrated in figure 8 as a kind of concrete implementation of turn-offing control module 14, described shutoff control module 14 comprises that switching tube conduction detection delay circuit, switching tube close the detection delay circuit; Rest-set flip-flop and logic combination circuit, described switching tube conduction detection delay circuit comprises metal-oxide-semiconductor M4, capacitor C 1; Current source I1, inverter N1, inverter N2, inverter N3, said switching tube close the detection delay circuit and comprise metal-oxide-semiconductor M5; Capacitor C 2, current source I2, inverter N4, inverter N5; Signal S1 is through the grid of inverter N1 connection M4, and the drain electrode of said M4 is connected the two ends of capacitor C 1, the source ground of M4 with source electrode; The drain electrode of M4 connects current source I1, and the drain electrode of M4 simultaneously is through inverter N2, N3 reversed-phase output signal S2, and signal S2 connects the S end of rest-set flip-flop; The connection of said M5, capacitor C 2, inverter N4, N5 is identical with the connection of described M4, C1, N2, N3; The output of inverter N5 connects the R end of rest-set flip-flop, and the Qn end of rest-set flip-flop connects the grid of M5, and the Q end of signal S2, rest-set flip-flop and Vc acting in conjunction are in logic combination circuit; Output signal S3; Logic combination circuit shown in Figure 8 is that the Q end of N3 reversed-phase output signal S2, rest-set flip-flop connects NOR gate 150 and through an end of inverter anti-phase input NOR gate 151, and Vc is through the other end of inverter anti-phase input NOR gate 151, NOR gate 151 output signal S3;

The S3 signal of described shutoff control module 14 outputs strengthens through driver DR1; Produce signal PWM, signal PWM1 and signal S1; The grid of signal PWM input switch pipe M1; Signal PWM1 feeds back to the M2 grid of sampling and threshold setting module 10, changes the voltage sampling signal Vs of sampling and threshold setting module 10, and signal S1 feeds back to and turn-offs control module 14.

Led drive circuit shown in Figure 6, the rated output voltage at the LED load two ends in input voltage vin and external led circuit differ hour, and its driving method is:

Led drive circuit and external led circuit initially power on, and the voltage generator VREF1 of the sampling of led drive circuit and threshold setting module 10 produces setting threshold signal Vt, the voltage on led drive circuit Vin port and the CS port sampling Rsense; Amplifier A1, M3 and the resistance R 1 of sampling and threshold setting module 10; R2, R3 forms voltage amplifier circuit, and the voltage on the Rsense is amplified; Produce sampled voltage Vs, the size of Vs voltage is:

$\mathrm{Vs}=\frac{\mathrm{Rsense}\&times;I_{L3}}{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="H2009100962180E00032.png"\; state="\{\{state\}\}">R</figure-callout>}1}\&times;(\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="H2009100962180E00042.png"\; state="\{\{state\}\}">R</figure-callout>}2+R3)$

Voltage sampling signal Vs and setting threshold signal Vt compare through comparator A2, and the voltage of comparator A2 output comparison signal Vc is low, and it is low turn-offing control module output signal S3; After signal S3 strengthened through driver DR1, the voltage of output signal PWM was high, switching tube M1 conducting; The SW port is output as low level; Synchronous signal PWM1 is high, the M2 conducting, and this moment, Vs voltage became:

$\mathrm{Vs}=\frac{\mathrm{Rsense}\&times;I_{L3}}{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="H2009100962180E00032.png"\; state="\{\{state\}\}">R</figure-callout>}1}\&times;\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="H2009100962180E00042.png"\; state="\{\{state\}\}">R</figure-callout>}2$

The Rsense of the external led circuit of Vin process, the LED load, L1, switching tube M1 is to the branch road conducting on ground, and this branch road has electric current I _L3Occur, because inductance L 1 is an energy-storage travelling wave tube, I _L3Be an electric current that increases gradually from small to large, because the output voltage pressure reduction at the LED load two ends in input voltage vin and the external led circuit is less, I _L3Maximum do not reach the size of maximum current Imax all the time, just Vs is less than Vt, switching tube M1 this moment conducting always,

Maximum current Imax is:

$I\max =\frac{\mathrm{Vt}\&times;R1}{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="H2009100962180E00042.png"\; state="\{\{state\}\}">R</figure-callout>}2\&times;\mathrm{Rsense}}$

Minimum current I min is:

$I\min =\frac{\mathrm{Vt}\&times;R1}{(\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="H2009100962180E00042.png"\; state="\{\{state\}\}">R</figure-callout>}2+R3)\&times;\mathrm{Rsense}}$

The time that the S1 input switching tube M1 of driver DR1 output opens, the course of work of switching tube conduction detection delay circuit is: when switching tube M1 conducting, the S1 signal is high, inverter N1 output low level; Not conducting of M4, current source I1 is to capacitor C 1 charging, and the A point current potential between current source I1 and the capacitor C 1 improves; Through the t1 time, when A point current potential is elevated to the turnover voltage V1 of inverter N2, inverter N2; The N3 upset, signal S2 becomes high level, and the Q end level of rest-set flip-flop is uprised by low; Qn end level is by high step-down, and S2 end level uprises and Q end level uprises control signal S3 end level step-down, pwm signal step-down; Switching tube M1 turn-offs, while S1 signal step-down, S2 signal step-down; Switching tube is closed the course of work that detects delay circuit: S2 is uprised by low, and Qn holds level by high step-down, not conducting of M5; I2 gives capacitor C 2 chargings, through the t2 time, when the B point voltage between current source I2 and the capacitor C 2 is elevated to the turnover voltage V2 of inverter N4; Inverter N4, N5 overturns, and the R end of rest-set flip-flop uprises; Q holds step-down, behind the wait Q end level step-down, and NAND gate 150 output high level; Because the Vc level is always low, makes the S3 signal uprise, pwm signal uprises; Switching tube M1 conducting, like this, pwm signal is for continuing t1 time high level; Duration is the low level fixed pulse width signal of t2, and after after a while, it is stable that output waveform reaches; Outputting current steadily; Said t1 is by I1, and the size of the turnover voltage V1 of C1 and inverter determines that t2 is by I2; The turnover voltage V2 size decision of C2 and inverter, computing formula is: can control the size of output current through control t1 and t2 time.Aforesaid signal waveform is as shown in Figure 9, and S1, S3 are respectively two signals among Fig. 8, and Q is the Q end output signal of rest-set flip-flop among Fig. 8, and Imax is the max-thresholds electric current of inductive current, and Imin is the minimum threshold electric current of inductive current, I _L3Be the inductive current waveform, Iout2 is not for adding the output average current that turn-offs control module, and Iout3 is the output average current after control module is turn-offed in increase.The rated output voltage at the LED load two ends of led drive circuit shown in Figure 6 in input voltage vin and external led circuit differs hour; The mean value of output current is much smaller than max-thresholds electric current I max value; Thereby reach the purpose of current limliting; Can see that by sequential chart Iout3 has had significantly than Iout2 and reduces.

The circuit diagram of led drive circuit as shown in Figure 7 is a kind of variation of Fig. 6, and wherein, sampling described in Fig. 7 comprises that with the amplifying circuit of threshold setting module amplifier A1, metal-oxide-semiconductor M3, resistance R 1, resistance R 2, described Vin port are connected the negative input end of comparator A1 through resistance R 1; The CS port connects the positive input terminal of comparator A1, and the output of comparator A1 connects the grid of M3, and the source electrode of M3 is connected the other end and the resistance R 2 of resistance R 1 respectively with draining; The other end ground connection of resistance R 2, the SE1 among Fig. 7 is a selector, VREF2 is a voltage generator; Produce maximum voltage Vmax and two kinds of voltages of minimum voltage Vin; When PWM1 signal when being high, selector SE1 with Vmax output as Vt, when the signal of PWM1 when low; Selector exports Vmin as setting threshold signal Vt; With respect to PWM1 signal change sample voltage value Vs among Fig. 6, Fig. 7 is through PWM1 signal change setting threshold signal Vt, and both purposes are max-thresholds and the minimum threshold that produces inductive current; Be that concrete implementation is different, its operation principle is identical with Fig. 6.

The invention discloses led drive circuit and driving method thereof, and illustrate and describe embodiment of the present invention and effect.What should be understood that is; The foregoing description is just to explanation of the present invention; Rather than limitation of the present invention; Any innovation and creation that do not exceed in the connotation scope of the present invention, include but not limited to the composition mode of turn-offing control module modification, to the change of the local structure of circuit, like the time detection circuit that turn-offs control module among replacement the present invention, increase reduce logic control, to the replacement of the type or the model of components and parts; And the replacement of other unsubstantialities or modification etc., all fall within the protection range of the present invention.

Claims (11)

1.LED drive circuit is characterized in that comprising sampling and threshold setting module, comparison module, shutoff control module, driver module and switch module:

Said sampling and the Vin port of threshold setting module are connected the sampling resistor Rsense two ends of external led circuit with the CS port; The voltage of sampling Rsense; And be voltage sampling signal Vs with the amplifying circuit of threshold setting module with the voltage amplification on the Rsense through sampling; Sampling simultaneously produces setting threshold signal Vt with the threshold setting inside modules, and voltage sampling signal Vs and setting threshold signal Vt input comparison module compare, and the Vin port of said sampling and threshold setting module inserts external input voltage; The PWM1 port connects driver module, sampling and threshold setting module ground connection;

Said comparison module produces comparison signal Vc input and turn-offs control module;

Said shutoff control module is accepted the feedback of driver module simultaneously, produces signal S3 input driver module;

Said driver module produces signal PWM, signal PWM1 and signal S1, signal PWM input switch module,

Signal PWM1 feeds back to sampling and threshold setting module, changes the voltage sampling signal Vs or the setting threshold signal Vt of sampling and threshold setting module, and signal S1 feeds back to the shutoff control module;

The output port SW of said switch module controls the break-make of external led circuit, switch module ground connection;

When the LED of led drive circuit input voltage vin and external led circuit load two ends rated output voltage differs hour, the high level time of signal S1 that detects driver module output when the shutoff control module of led drive circuit is when turn-offing the setting-up time t1 of control module, and the output signal S3 that turn-offs control module is after driver module strengthens; The pwm signal step-down of control and driving module output, switch module turn-offs, and turn-offs control module signal S3 is delayed time t2 after the time; Signal S3 overturns once more, and signal S3 is after driver module drives enhancing, and the output signal PWM of control and driving module uprises; The switch module conducting; SW port output low level, pwm signal is for continuing t1 time high level, and the duration is the low level fixed pulse width signal of t2; After after a while, the led drive circuit output waveform reaches stable.

2. led drive circuit according to claim 1 is characterized in that the amplifying circuit of said sampling and threshold setting module comprises amplifier A1, metal-oxide-semiconductor M3, metal-oxide-semiconductor M2, resistance R 1, resistance R 2, resistance R 3, and described Vin port connects the negative input end of comparator A1 through resistance R 1; The CS port connects the positive input terminal of comparator A1; The output of comparator A1 connects the grid of M3, and the source electrode of M3 is connected the other end and the resistance R 2 of resistance R 1 respectively with draining, resistance R 2, R3 series connection; The other end ground connection of R3; The drain electrode of M2 connects between resistance R 2 and the R3, and the source electrode of M2 connects resistance R 3 earth terminals, and the grid of M2 connects driver module.

3. led drive circuit according to claim 1; It is characterized in that the said sampling and the amplifying circuit of threshold setting module comprise that amplifier A1, metal-oxide-semiconductor M3, resistance R 1, resistance R 2, described Vin port are connected the negative input end of comparator A1 through resistance R 1; The CS port connects the positive input terminal of comparator A1, and the output of comparator A1 connects the grid of M3, and the source electrode of M3 is connected the other end and the resistance R 2 of resistance R 1 respectively with draining; The other end ground connection of resistance R 2; Said sampling and threshold setting module also comprise voltage generator VREF2 and selector SE1, and maximum voltage Vmax, minimum voltage Vmin that voltage generator VREF2 produces offer selector SE1, driver module output signal PWM1 input selector SE1; Control selector output maximum voltage Vmax or minimum voltage Vmin are as setting threshold signal Vt.

4. led drive circuit according to claim 1; That it is characterized in that said comparison module employing is comparator A2; The positive input terminal of comparator A2 connects voltage sampling signal Vs; The negative input end of comparator A2 connects the setting threshold signal Vt of sampling and the output of threshold setting module, and the output of comparator A2 produces comparison signal Vc.

5. led drive circuit according to claim 1 is characterized in that said switch module adopts switching tube M1, and the grid of M1 connects the driver DR1 of driver module, the source ground of M1, and the drain electrode of M1 is as the SW output of led drive circuit.

6. led drive circuit according to claim 1; It is characterized in that said shutoff control module comprises that switching tube conduction detection delay circuit, switching tube are closed and detects delay circuit, rest-set flip-flop and logic combination circuit; Described switching tube conduction detection delay circuit is at the high level time of the S1 signal that detects driver module output during greater than switching tube conduction detection delay circuit setting-up time t1; With rest-set flip-flop and logic combination circuit effect, final stopcock module; Described switching tube is closed the detection delay circuit and is detected S3 signal low level time-delay t2 after the time, with rest-set flip-flop and logic combination circuit effect, and final actuating switch module.

7. like the said led drive circuit of claim 6, it is characterized in that described switching tube conduction detection delay circuit comprises metal-oxide-semiconductor M4, capacitor C 1; Current source I1, inverter N1, inverter N2, inverter N3, said switching tube close the detection delay circuit and comprise metal-oxide-semiconductor M5; Capacitor C 2, current source I2, inverter N4, inverter N5; Signal S1 is through the grid of inverter N1 connection M4, and the drain electrode of said M4 is connected the two ends of capacitor C 1, the source ground of M4 with source electrode; The drain electrode of M4 connects current source I1, and the drain electrode of M4 simultaneously is through inverter N2, N3 reversed-phase output signal S2, and signal S2 connects the S end of rest-set flip-flop; The connection of described M5, capacitor C 2, inverter N4, N5 is identical with the connection of described M4, C1, N2, N3; The output of inverter N5 connects the R end of rest-set flip-flop, and the Qn end of rest-set flip-flop connects the grid of M5, and the Q end of signal S2, rest-set flip-flop and Vc acting in conjunction are in logic combination circuit; Output signal S3; Described logic combination circuit is that the Q end of N3 reversed-phase output signal S2, rest-set flip-flop connects NOR gate 150 and through an end of inverter anti-phase input NOR gate 151, and Vc is through the other end of inverter anti-phase input NOR gate 151, NOR gate 151 output signal S3.

8. led drive circuit according to claim 1 is characterized in that the amplifying circuit of said sampling and threshold setting module comprises amplifier A1, metal-oxide-semiconductor M3, metal-oxide-semiconductor M2, resistance R 1, resistance R 2, resistance R 3, and described Vin port connects the negative input end of comparator A1 through resistance R 1; The CS port connects the positive input terminal of comparator A1; The output of comparator A1 connects the grid of M3, and the source electrode of M3 is connected the other end and the resistance R 2 of resistance R 1 respectively with draining, resistance R 2, R3 series connection; The other end ground connection of R3; The drain electrode of M2 connects between resistance R 2 and the R3, and the source electrode of M2 connects resistance R 3 earth terminals, and the grid of M2 connects driver module; Said switch module adopts switching tube M1, and the grid of M1 connects the driver DR1 of driver module, the source ground of M1, and the drain electrode of M1 is as the SW output of led drive circuit.

9. like the said led drive circuit of claim 8; The S3 signal that it is characterized in that said shutoff control module output strengthens through driver DR1; Produce signal PWM, signal PWM1 and signal S1, signal PWM output connects the grid of switching tube M1, and signal PWM1 feeds back to the grid of sampling and threshold setting module M2; Change the voltage sampling signal Vs or the setting threshold signal Vt of sampling and threshold setting module, signal S1 feeds back to the shutoff control module.

10.LED the driving method of drive circuit is characterized in that:

When the LED of led drive circuit input voltage vin and external led circuit load two ends rated output voltage differs hour, led drive circuit and external led circuit initially power on, and the voltage sampling signal Vs that the sampling of led drive circuit and threshold setting module are exported is less than setting threshold signal Vt; The switch module SW port output low level of led drive circuit, the high level time of S1 signal that detects driver module output when the shutoff control module of led drive circuit is when turn-offing the setting-up time t1 of control module, and the output signal S3 that turn-offs control module is after driver module strengthens; The pwm signal step-down of control and driving module output, switch module turn-offs, and turn-offs control module with S3 signal lag t2 after the time; Signal S3 overturns once more; S3 is after driver module drives enhancing, and the output pwm signal of control and driving module uprises, the switch module conducting; SW port output low level; Pwm signal is for continuing t1 time high level, and the duration is the low level fixed pulse width signal of t2, after after a while; The led drive circuit output waveform reaches stable; LED load outputting current steadily, led drive circuit Automatic Cycle said process realizes that led drive circuit drives the stagnant ring of external led circuit.

11. the driving method like the said led drive circuit of claim 10 is characterized in that:

When the LED of led drive circuit input voltage vin and external led circuit load two ends rated output voltage differed big, led drive circuit and external led circuit initially powered on, and the voltage sampling signal Vs of the sampling of led drive circuit and the output of threshold setting module is less than setting threshold signal Vt; The SW port output low level of the switch module of led drive circuit; The service time of switch module, the S1 signal of driver module output can not cause the upset of the S3 signal that turn-offs control module output less than the time t1 of the setting of turn-offing control module, and the S3 signal is only determined by the output voltage V c of comparison module; When voltage sampling signal Vs increases to setting threshold signal Vt; The output voltage V c of comparison module overturns, and turn-offs the output signal S3 upset of control module then, thereby causes the output signal PWM upset of driver module; Switch module turn-offs; Simultaneously the output signal PWM1 of driver module increases sampled voltage Vs moment perhaps the Vt signal is reduced to minimum value by maximum moment, and when voltage sampling signal Vs was reduced to setting threshold signal Vt subsequently, comparison module overturn once more; Driver module output signal PWM overturns once more; The switch module conducting, simultaneously the PWM1 signal reduces voltage sampling signal Vs moment or setting threshold signal Vt is increased to maximum by minimum value moment, after after a while; The output waveform of led drive circuit reaches stable; LED load outputting current steadily, led drive circuit Automatic Cycle said process realizes that led drive circuit drives the stagnant ring of external led circuit.

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