CN104010421B - Constant current output control device for LED drive circuit - Google Patents

Abstract

The invention relates to an electronic circuit technology, in particular to a constant current output control device for an LED drive circuit. The constant current output control device comprises a drive circuit and a BUCK circuit and is characterized by further comprising a time balancing module, a time control module and an average current sampling module; the time balancing module is connected with the drive circuit, the time control module and the average current sampling module; the BUCK circuit is connected with the drive circuit and the average current sampling module; the time balancing module is used for outputting breakover signals through the drive circuit, and controlling time for making currents in the BUCK circuit change from the minimum value to a current average value to be equal to time for making currents change from the current average value to a peak value. The time control module is used for outputting turn-off signals through the drive circuit. The constant current output control device has the advantages that the problem that output currents in the drive circuit are affected by parameters of input voltages, output voltages and inductance is solved, and constant current output stability is greatly improved. The constant current output control device is especially suitable for the LED drive circuit.

Description

A kind of constant current output controller for led drive circuit

Technical field

The invention belongs to electronic circuit technology, (buck circuit is a kind of based on buck circuit to particularly relate to one kind The buck topology mode of dc-dc) led drive circuit constant current output numerical control device.

Background technology

Led with its long-life, brightness height, stable performance, pollution-free the features such as become the green lighting technique of today's society. For the drive circuit of led, if led adopts common source of stable pressure to drive, when voltage somewhat fluctuates, by LED lamp Current fluctuation is very big, be easy to occur brightness is unstable in addition over-current phenomenon avoidance and burn led, so current led generally uses perseverance Stream mode is driven.

As shown in figure 1, being a kind of schematic diagram of the output constant current circuit based on buck topology on traditional approach.This circuit master Including fly-wheel diode d, switching tube q, energy storage inductor l, load LED lamp, detection resistance r, switching tube control circuit.Substantially Operation principle is: when switching tube q opens, electric current flows through led, inductance l and resistance r and forms loop, and led lights, simultaneously inductance l and Electric capacity c energy storage, sampling resistor r detects the current waveform by inductance, and the current value on switching tube q switchs after reaching predetermined value Pipe turns off, and energy storage inductor l and electric capacity c continues to led load supplying by fly-wheel diode d and load composition loop, and led sends out Light.

As shown in Fig. 2 being the output current wave figure on traditional approach, il be energy storage inductor l on electric current, ilow be for By the minimum of a value of inductance l electric current, ipeak is the peak point current by inductance, and im is average current, that is to say the output of requirement Electric current, in its abscissa, ton represents the opening time of switching tube q, and toff represents the turn-off time of switching tube q.Work as control circuit When making switching tube q open ton, the electric current linear rise on energy storage inductor, until the voltage that sampling resistor r samples makes control electricity Comparator upset within road, control circuit meeting on-off switching tube q, the time is toff, electric current linear decline on energy storage inductor, such as This define output current wave repeatedly.

This basic current constant control structure is simple, but circuit has what output current was affected by peripheral circuit parameter Inherent defect.Definition current ripples amount is △ i=ipeak-ilow, under continuous current mode (ccm), then averagely Electric current isThat is to sayAccording to circuit analysis, electric current on inductance Linearly increasing or decline, in ccm (continuous current mode) MODE of operation, $\mathrm{\δi}={\&integral;}_0^{\mathrm{ton}}\frac{\mathrm{vin}-\mathrm{vo}}{l}\mathrm{dt}=\frac{\mathrm{vin}-\mathrm{vo}}{l}\mathrm{ton}=-\frac{\mathrm{vo}}{l}\mathrm{toff}.$ This just illustrates to determine peak value electricity using sampling resistor Stream ipeak, average output current also suffers from input voltage vin, output voltage vo, the isoparametric impact of inductance l, these factors Slightly deviation, the average current im of output is just no longer constant.

Content of the invention

The purpose of the present invention is it is simply that affected by peripheral circuit parameter for output current present in above-mentioned conventional art Problem, a kind of constant current output controller for led drive circuit is proposed so that output current and input voltage, output The parameters such as voltage, inductance are unrelated.

The present invention solves above-mentioned technical problem and be the technical scheme is that a kind of constant current for led drive circuit is defeated Go out control device, including drive circuit and buck circuit it is characterised in that also including time equalization module, time control module With average current sample module；Time equalization module respectively with drive circuit, time control module and average current sample module Connect；Buck circuit is connected with drive circuit and average current sample module respectively；Time equalization module is used for by driving electricity Road output conducting signal, control buck circuit in the time from minimum of a value to current average for the electric current be equal to current average to The time of peak point current；Time control module is used for the signal turning off by drive circuit output；Wherein,

Buck electric routing switch pipe q1, inductance l1, electric capacity c1 and diode d1 are constituted；Wherein, the drain electrode of switching tube q1 according to Secondary power supply vin is followed by by inductance l1, electric capacity c1, the drain electrode of switching tube q1 connects the positive pole of diode d1；The negative pole of diode d1 Meet power supply vin；

Time equalization module is made up of the first phase inverter, forward-backward counter and OR gate；Wherein, the output end of forward-backward counter Connect the input of OR gate；The output of OR gate terminates the input of drive circuit and the first phase inverter；The output end of the first phase inverter Connect the input of forward-backward counter；

Time control module constituted by the second phase inverter, the 3rd phase inverter, up counter and with door；Wherein, second is anti- The input of phase device terminates the output end of OR gate, the additive signal end of its output termination up counter；The input of the 3rd phase inverter The output end of termination OR gate, the input of its output termination up counter；The output termination of up counter and the input of door End；Output with door terminates the input of OR gate；

Average current sampling module is made up of comparator and resistance r1；Wherein, the negative-phase input of comparator connects switching tube The source electrode of q1, its positive input meets reference voltage vr, and its output terminates the up-down signal end of forward-backward counter and the defeated of OR gate Enter end；The source electrode of switching tube q1 is grounded gnd after resistance r1.

Beneficial effects of the present invention are to solve output current in drive circuit and joined by input voltage, output voltage, inductance The problem of number impact, greatly improves the stability of constant current output, simultaneously because control section adopts digit chip, becomes well The nearly development trend with current integrated circuit, has the advantages that strong antijamming capability, saves chip area, is easy to precise control.

Brief description

Fig. 1 is traditional led constant current circuit structure schematic diagram based on buck topology；

Fig. 2 is the output current schematic diagram of circuit shown in Fig. 1；

Fig. 3 is the electrical block diagram of embodiment；

Fig. 4 is pulse sequence figure and the output current schematic diagram of embodiment.

Specific embodiment

With reference to the accompanying drawings and examples, describe technical scheme in detail

Constant current output controller for led drive circuit proposed by the present invention, using time equalization module and time Control module carries out Discrete control to the current rise time on inductance in buck circuit so that the output of average current and input Voltage, output voltage, energy storage inductor are all unrelated, have reached stability contorting output current.

Embodiment:

As shown in figure 3, this example include drive circuit, buck circuit, time equalization module, time control module and averagely electricity Stream sampling module；Time equalization module is connected with drive circuit, time control module and average current sample module respectively；buck Circuit is connected with drive circuit and average current sample module respectively；Time equalization module is used for exporting conducting by drive circuit Signal, control buck circuit in the time from minimum of a value to current average for the electric current arrive peak point current equal to current average Time；Time control module is used for the signal turning off by drive circuit output；Wherein,

Buck electric routing switch pipe q1, inductance l1, electric capacity c1 and diode d1 are constituted；Wherein, the drain electrode of switching tube q1 according to Secondary power supply vin is followed by by inductance l1, electric capacity c1, the drain electrode of switching tube q1 connects the positive pole of diode d1；The negative pole of diode d1 Meet power supply vin；

Time equalization module is made up of the first phase inverter n1, forward-backward counter b1 and OR gate u1；Wherein, what this example adopted adds The chip model of down counter b1 be 74s169, it includes input d0, d1, d2, d3, add-subtract control port u d, input enable End ent, enp, insert control end ldn, clock signal port clk, output port q0, q1, q2, q3, tcn.Forward-backward counter b1 Add-subtract control port u d be high level when, b1 execution plus count, when add-subtract control port u d be low level when, b1 execution subtract Count；Input Enable Pin ent, enp is Low level effective, orders about chip operation；Inserting control end ldn is Low level effective, opens The data of beginning receives input end q0, q1, q2, q3 input；Clock signal port clk receives external clock control signal；Carry is defeated Exit port tcn does not use in this example.Output port q0, q1, q2, q3 of forward-backward counter b1 connect the input of OR gate u1； The output of OR gate u1 terminates the input of drive circuit and the first phase inverter n1；The output termination plus-minus counting of the first phase inverter n1 Input port ent, enp, ldn of device b1；

Time control module constituted by the second phase inverter n2, the 3rd phase inverter n3, up counter b2 and with door u2；Its In, the chip model of the addition technology device that this example adopts is 74163, and it includes addition control port ldn, input port a, b, c, D, inputs Enable Pin ent, enp, counts clear terminal clrn, clock signal port clk, output port qa, qb, qc, qd, rco.Plus Addition control port ldn of counter b2 is Low level effective, and execution adds counting；Input Enable Pin ent, enp has for high level Effect, orders about chip operation；Counting clear terminal clrn is Low level effective；Clock signal port clk receives external clock control letter Number；Carry-out port rco does not use in this example.The input of the second phase inverter n2 terminates the output end of OR gate u1, and it is defeated Go out to terminate addition control port ldn of up counter；The input of the 3rd phase inverter n3 terminates the output end of OR gate u1, its output Ent, enp, clrn input of termination up counter；The output termination of up counter and the input of door u2；With door u2 Output terminate OR gate u1 input；

Average current sampling module is made up of comparator a1 and resistance r1；Wherein, the negative-phase input of comparator a1 connects out Close the source electrode of pipe q1, its positive input meets reference voltage vr, the add-subtract control end u d of its output termination forward-backward counter and/or The input of door；The source electrode of switching tube q1 is grounded gnd after resistance r1.

The operation principle of this example is:

During original state, the electric current on inductance l1 is less than average current im, and sampling resistor r1 detects negative for comparator a1 Terminal voltage be less than reference voltage vr, now comparator a1 output high level, be delivered to OR gate u1 be output as high level so that Obtain the work of drive circuit module driving switch pipe, be the t1 stage of ON time ton.Now counter b2 Enable Pin ent, Enp is low level, and counter b2 does not work, and is output as 0 state.High level controls the add-subtract control of forward-backward counter b1 simultaneously Port u d end start execution plus count.When on inductance electric current linear rise to during more than average current im, comparator a1 overturns, Output low level, now the add-subtract control port u of low level control forward-backward counter b1 d end start execution and subtract counting, but by Must there is 1 presence in a certain state q0, q1 that the is t1 time plus counting down to, q2, q3, so now OR gate output is still High level driving power pipe q1 works, and is the t2 stage of ON time ton, until forward-backward counter b1 subtracts counting stage in execution So that output q0, q1, q2, q3 all 0, t2 time terminates, OR gate u1 output is changed into low level, and switching tube q1 closes end, during ton Between terminate, final t1=t2.

Then due to forward-backward counter b1 Enable Pin ent, enp does not work for high level, counter b2 Enable Pin ent, Enp starts working for high level, so off time control module starts the time toff of controlling switch pipe q1 shutoff.Electric discharge rank Section starts counting up, and sets a gate time length, such as clock signal period is t μ s, count down to 17 clocks of 1111 counting In the cycle, count discharge length 17t μ s, this section of counter b2 exports low level, so OR gate u1 output low level, switching tube pass Disconnected.When counting down to 1111, order about switching tube work with door u2 output high level.So switching tube turn-off time toff rank Section terminates.

This two stages go round and begin again, thus defining the pulse sequence figure of circuit as of the present invention in Fig. 4 and output current is shown It is intended to, in its abscissa, ton represents the opening time of switching tube q, toff represents the turn-off time of switching tube q so that switching tube In the conducting ton time, inductive current rises to time t1 used by average current im from minimum of a value ilow and is equal to inductive current from flat All electric current im rise to time t2 used by peak point current ipeak, can verify from figure, the electric current on inductance is in different risings Average current im under slope is unrelated with the slope of output ripple, that is to say unrelated with output voltage, input voltage, inductance value.

In summary it can be seen, compare the output constant current circuit of basic buck topology in Fig. 1, present invention improves over it is intrinsic Some shortcomings, using switching tube conducting during time slice control so that from minimum output current to average value current Time, and the time from average value current to peak point current is equal, so that the slope of output current and ripple is unrelated, output The stability characteristic (quality) of electric current has obtained larger lifting.Simultaneously because control section adopts digit chip, level off to well at present The development trend of integrated circuit, has the advantages that strong antijamming capability, saves chip area, is easy to precise control.

Claims (1)

1. a kind of constant current output controller for led drive circuit, including drive circuit and buck circuit, its feature exists In also including time equalization module, time control module and average current sample module；Time equalization module is electric with driving respectively Road, time control module and average current sample module connect；Buck circuit respectively with drive circuit and average current sample mould Block connects；Time equalization module is used for the signal by drive circuit output conducting, and in control buck circuit, electric current is from minimum of a value Time to current average is equal to current average to the time of peak point current；Time control module is used for by drive circuit The signal that output turns off；Wherein,

Buck electric routing switch pipe q1, inductance l1, electric capacity c1 and diode d1 are constituted；Wherein, the drain electrode of switching tube q1 is led to successively Cross inductance l1, electric capacity c1 is followed by power supply vin, the drain electrode of switching tube q1 connects the positive pole of diode d1；The negative pole of diode d1 connects electricity Source vin；

Time equalization module is made up of the first phase inverter, forward-backward counter and OR gate；Wherein, forward-backward counter output termination or The input of door；The output of OR gate terminates the input of drive circuit and the first phase inverter；The output termination of the first phase inverter adds The input of down counter；

Time control module constituted by the second phase inverter, the 3rd phase inverter, up counter and with door；Wherein, the second phase inverter Input terminate OR gate output end, its output termination up counter additive signal end；The input termination of the 3rd phase inverter The output end of OR gate, the input of its output termination up counter；The output termination of up counter and the input of door；With The output of door terminates the input of OR gate；

Average current sampling module is made up of comparator and resistance r1；Wherein, the negative-phase input of comparator connects switching tube q1's Source electrode, its positive input meets reference voltage vr, and its output terminates up-down signal end of forward-backward counter and the input of OR gate； The source electrode of switching tube q1 is grounded gnd after resistance r1.