CN104202869A - Constant-current control circuit, LED driving circuit and constant-current control method - Google Patents
Constant-current control circuit, LED driving circuit and constant-current control method Download PDFInfo
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- CN104202869A CN104202869A CN201410387249.2A CN201410387249A CN104202869A CN 104202869 A CN104202869 A CN 104202869A CN 201410387249 A CN201410387249 A CN 201410387249A CN 104202869 A CN104202869 A CN 104202869A
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Abstract
The application provides a constant-current control circuit, an LED driving circuit and a constant-current control method. In the constant-current control circuit, when a main switching tube is switched to a first state, a first charging circuit and a second charging circuit start charging; a first comparison circuit compares a sampling signal for representing inductive current with a standard voltage, and the comparison result controls charging time of the first charging circuit; a second comparison circuit compares charging voltages of the first and second charging circuits, and the comparison result controls charging time of the second charging circuit; when the second charging circuit stops charging, the main switching tube in the LED driving circuit is switched to a second state from the first state for controlling the LED driving circuit to output a constant-current signal. And therefore, when achieving constant-current control, the constant-current control circuit does not need an external sampling resistor for sampling LED current, integration of the LED driving circuit is improved, and application range is wide.
Description
Technical field
The present invention relates to a kind of power electronic technology, be specifically related to a kind of constant-current control circuit, LED drive circuit and constant current control method.
Background technology
Along with the constantly bringing forth new ideas and developing rapidly of illuminating industry, energy-conservation and environmental protection becomes more and more important in addition, and LED throws light on as a kind of revolutionary energy-saving illumination technology, just in develop rapidly.But due to brightness and the light output intensity parameter correlation of LED lamp, it is directly proportional to its electric current and forward voltage drop, and varies with temperature and change.Therefore, LED drive circuit need to produce a constant current LED lamp is driven, and also just needs the constant-current control circuit that can control LED drive circuit and realize constant current output.
Fig. 1 is a kind of LED drive circuit of existing techniques in realizing, and described LED drive circuit comprises constant-current control circuit 01 and power stage circuit 02.In described power stage circuit 02, be provided with main switch S
wand inductance L; Described constant-current control circuit is for controlling described main switch S according to the output current feedback signal of LED drive circuit
wswitch motion, thereby make described LED drive circuit export a constant current signal; The feedback signal of described output current is by a sampling resistor R who connects with LED load
senseobtain, and output current feedback signal is transferred to described control circuit 01, therefore also need to comprise can be by sampling resistor R for described LED drive circuit
sensethe output current sample circuit forming.
Constant-current control circuit in LED drive circuit as shown in Figure 1, in the time realizing constant current control, need to utilize the external sampling resistance LED electric current of sampling, and non-essential resistance can not be integrated in the chip at described constant-current control circuit place, do not utilize like this integrated level of LED drive circuit system, can not improve the efficiency of system.
Summary of the invention
In view of this, the invention provides a kind of constant-current control circuit, LED drive circuit and constant current control method, need to be by sample the not high problem of integrated level of the LED drive circuit system that LED load current causes of non-essential resistance to solve in prior art in the time realizing constant current control.
A kind of constant-current control circuit, for LED drive circuit, is provided with main switch and inductance in described LED drive circuit, described constant-current control circuit comprises:
Inductive current sample circuit, crosses the inductive current of described inductance for sample streams, and exports the sampled signal of a described inductive current;
The first comparison circuit, for more described sampled signal and a reference voltage signal, and exports the first comparison signal;
The first charging circuit, comprises the first electric capacity, the first current source, and in very first time section, described the first current source is to described the first capacitor charging;
The second charging circuit, comprises the second electric capacity, the second current source, and within the second time period, described the second current source is to described the second capacitor charging;
The second comparison circuit, for the voltage on voltage and the second electric capacity on more described the first electric capacity, and exports the second comparison signal;
Pwm signal generation circuit, for generating pwm signal according to described the second comparison signal and one first control signal, switches between the first state and the second state to control described main switch, makes described LED drive circuit export a constant current signal;
In the time that described the first control signal is effective status, described main switch switches to described the first state and described very first time section and described the second time period to start to occur simultaneously, in the time that described sampled signal equals described reference voltage signal, described very first time section finishes, in the time that the voltage on described the second electric capacity equals the voltage on described the one the first electric capacity of section finish time described very first time, described the second time period finishes and described main switch switches to described the second state;
Described very first time section finishes before described the second time period finishes.
Preferably, described constant-current control circuit, also comprises inductive current sample circuit, and described inductive current sample circuit is connected with one end of described inductance, for the described inductive current of sampling, and exports described sampled signal.
Preferably, described constant-current control circuit, also comprise pwm signal generation circuit, described pwm signal generation circuit is for generating pwm signal according to described the second comparison signal and one first control signal, switch between described the first state and described the second state to control described main switch, make described LED drive circuit export a constant current signal, in the time that described the first control signal is effective status, described main switch switches to described the first state.
Preferably, described the first charging circuit also comprises the first switch, and the two ends of described the first switch are connected with the two ends of described the first electric capacity respectively;
Described the second charging circuit also comprises second switch, and the two ends of described second switch are connected with the two ends of described the second electric capacity respectively;
Described the first switch and described second switch all turn-off during described main open pipe is described the first state, conducting during described main open pipe is described the second state.
Preferably, described the first charging circuit also comprises the 3rd switch, and described the 3rd pass is connected between described the first current source and described the first electric capacity, the conducting in the time that described the first comparison signal is effective status of described the 3rd switch.
Preferably, described the first comparison circuit comprises one first comparator, and described the second comparison circuit comprises one second comparator, and described pwm signal generation circuit comprises a rest-set flip-flop;
The input in the same way of described the second comparator receives the voltage on described the second electric capacity, and backward end receives the voltage on described the first electric capacity, and output is exported described the second comparison signal.
Preferably, described the first state is conducting state, and described the second state is off-state.
Preferably, described the first state is off-state, and described the second state is conducting state.
Preferably, the in-phase input end of described the first comparator receives described reference voltage signal, and reverse input end receives described sampled signal, and output is exported described the first comparison signal;
The RESET input of described rest-set flip-flop receives described the second comparison signal, and set income termination is received described the first control signal.
Preferably, the in-phase input end of described the first comparator receives described sampling, and reverse input end receives described reference voltage signal, and output is exported described the first comparison signal;
The RESET input of described rest-set flip-flop receives described the first control signal, and set income termination is received described the second comparison signal.
A kind of LED drive circuit, comprises a power stage circuit, is provided with main switch and inductance in described power stage circuit, also comprises the constant-current control circuit described in above-mentioned any,
Described constant-current control circuit is exported a pwm signal, to control the switch motion of described main switch, makes described LED drive circuit export a constant current signal.
A kind of constant current control method, for LED drive circuit, is provided with main switch and inductance in described LED drive circuit, described method comprises:
Obtain the sampled signal that characterizes the inductive current that flows through described inductance;
In the time that described main switch switches to the first state, start with the first electric current the first capacitor charging, the second electric current is to the second capacitor charging;
In the time that described sampled signal equals a reference voltage signal, stop described the first capacitor charging;
When voltage on described the first electric capacity in the time that the voltage on described the second electric capacity equals to stop described the first capacitor charging, stop described the second capacitor charging, and control described main switch and switch to the second state by described the first state;
To the time period of described the first capacitor charging be designated as to very first time section;
Time period when to described the second capacitor charging was designated as for the second time period;
Described very first time section finishes before described the second time period finishes.
Therefore, the constant-current control circuit that adopts the application to provide, only need to utilize the first charging circuit and the second charging circuit in the time that main open pipe switches to the first state, all to start charging, then utilize sampled signal and the reference voltage that one first comparison circuit flows through a sign inductive current of inductance to compare, result is relatively for controlling the charging interval of the first charging circuit, again in order to the voltage of more described the second charging circuit of one second comparison circuit and the first charging circuit, result is relatively for controlling the charging interval of the second charging circuit, so in the time that stopping charging, described the second charging circuit make the main switch in described LED drive circuit switch to the second state by the first state, thereby control LED drive circuit and export a constant current signal.Therefore, the constant-current control circuit that the application provides need not be by the external sampling resistance LED electric current of sampling in the time realizing constant current control, effectively raise the integrated efficiency of LED drive circuit, and can be applicable to, in various types of LED drive circuits, have wide range of applications.
Brief description of the drawings
In order to be illustrated more clearly in the embodiment of the present invention or technical scheme of the prior art, to the accompanying drawing of required use in embodiment or description of the Prior Art be briefly described below, apparently, accompanying drawing in the following describes is only embodiments of the invention, for those of ordinary skill in the art, do not paying under the prerequisite of creative work, other accompanying drawing can also be provided according to the accompanying drawing providing.
Fig. 1 is the structure chart of a kind of LED drive circuit of existing techniques in realizing;
Fig. 2 is the structure chart of the disclosed a kind of constant-current control circuit of the embodiment of the present application;
Fig. 3 is the structure chart of the disclosed another kind of constant-current control circuit of the embodiment of the present application;
Fig. 4 is the disclosed another kind of constant-current control circuit working waveform figure of the embodiment of the present application;
Fig. 5 is the structure chart of disclosed another constant-current control circuit of the embodiment of the present application;
Fig. 6 is disclosed another the constant-current control circuit working waveform figure of the embodiment of the present application;
Fig. 7 is the schematic flow sheet of the disclosed a kind of constant current control method of the embodiment of the present application.
Embodiment
Below in conjunction with the accompanying drawing in the embodiment of the present invention, the technical scheme in the embodiment of the present invention is clearly and completely described, obviously, described embodiment is only the present invention's part embodiment, instead of whole embodiment.Based on the embodiment in the present invention, those of ordinary skill in the art, not making the every other embodiment obtaining under creative work prerequisite, belong to the scope of protection of the invention.
Fig. 2 is the structure chart of the disclosed a kind of constant-current control circuit of the embodiment of the present application.
Referring to Fig. 1, the disclosed described constant-current control circuit of the embodiment of the present application is applied in LED drive circuit, be particularly useful in the LED drive circuit of continuous mode, described LED drive circuit comprises power stage circuit 02, in described power stage circuit 02, is provided with main switch S
wand inductance L, described constant-current control circuit 01 is for controlling described main switch S
wswitch motion, export a constant current signal to control described LED drive circuit, LED load is normally worked.Described constant-current control circuit 01 comprises inductive current sample circuit 011, the first comparison circuit 012, the first charging circuit 013, the second charging circuit 014, the second comparison circuit 015 and pwm signal generation circuit 016.
Wherein, described inductive current sample circuit 011 is crossed the inductive current I of described inductance L for sample streams
l, and export described inductive current I
lsampled signal V
sen;
Described the first comparison circuit 012 is for more described sampled signal V
senwith a reference voltage signal V
ref, and export the first comparison signal Q1;
Described the first charging circuit 013 comprises the first electric capacity and the first current source, and in very first time section, described the first current source is to described the first capacitor charging;
Described the second charging circuit 014 comprises the second electric capacity and the second current source, and within described the second time period, described the second current source is to described the second capacitor charging;
Described the second comparison circuit 015 is for the voltage V on more described the first electric capacity
c1with the voltage V on described the second electric capacity
c2, and export the second comparison signal Q
2;
Described pwm signal generation circuit is used for according to described the second comparison signal Q
2with one first control signal V
crgenerate pwm signal, to control described main switch S
wbetween the first state and the second state, switch, make described LED drive circuit export a constant current signal;
At described the first control signal V
crduring for effective status, described main switch S
wswitch to described the first state and described very first time section and described the second time period all start occur, as described sampled signal V
senvalue while equaling the value of described reference voltage signal, described very first time section finishes, as the voltage V on described the second electric capacity
c2voltage V on described the first electric capacity while equaling section finish time described very first time
c1time, described the second time period finishes and described main switch switches to described the second state;
Described very first time section finishes before described the second time period finishes.
In the disclosed constant-current control circuit of the embodiment of the present application, described the first state is the one in conducting state and off state, and described the second state is the another kind in conducting state and off state.Taking described the first state as conducting state, described the second state is off state, and described the first current source is I
1, described the first electric capacity is C
1, described the second current source is I
2, described the second electric capacity is C
2, the topological structure of the power stage circuit 02 of described LED drive circuit is voltage-dropping type, mode of operation is that continuous current mode type is that example realizes the constant current control course of work to the disclosed constant-current control circuit of the embodiment of the present application and is:
As described the first control signal V
crduring for effective status, (effective status refers to that the first control signal triggers described main switch S
wresiding state while entering conducting state, for example, in the time of described the first control signal external timing signal, its effective status can refer to the rising edge of described the first control signal, when described the first control signal can be controlled described main switch S for other
wwhen the signal of conducting, its effective status can refer to other form, as high level etc.), main switch S described in the pwm signal control of described control circuit output
wswitch to conducting state, described very first time section T
1with described the second time period T
2(in all embodiment, all described very first time section is designated as to T in the present embodiment and below
1, described the second time period is designated as T
2) start to occur, now, described the first current source I
1start the first capacitor C
1charging, described the second current source I
2start the second capacitor C
2charging, and incite somebody to action now described inductive current I
lvalue be designated as I
l1, and make sampled signal V
sen=k
1× I
l, k
1for sampling coefficient, sampled signal V now
sen=k
1× I
l1;
Described main switch S
wenter after conducting state described inductive current I
lvalue by I
l1starting increases, i.e. described sampled signal V
sen=k
1× I
l1starting increases, as described inductive current I
lvalue by I
l1increase I
l2time, described sampled signal V
senequal described reference voltage signal V
ref, i.e. V
sen=k
1× I
l2=V
reftime, described the first comparison signal Q
1saltus step, makes described the first current source I
1stop described the first capacitor C
1charging, described very first time section T
1finish, and at described main switch S
wbefore switching to described the second state, keep the voltage V on described the first electric capacity
c1for described very first time section T
1the voltage of the finish time, i.e. V
c1=I
1× T
1/ C
1;
Described very first time section T
1after end, described the second time period T
2proceed described inductive current I
lvalue by I
l2continuing increases, described the second current source I
2continue the second capacitor C
2charging, when the second capacitor C
2on voltage V
c2the first capacitor C described in while equaling section finish time very first time
1on voltage V
c1time, i.e. V
c2=I
2× (T
1+ T
2)/C
2=V
c1=I
1× T
1/ C
1time, described the second time period T
2finish now described inductive current I
lvalue by I
l2be increased to I
l3, main switch S described in the pwm signal control of described control circuit output
wswitch to off state, described inductive current I
lvalue by I
l3start to decline, until the effective status of described the first control signal arrives again, described main switch switches to conducting state again, a new cycle, according to such working method, go round and begin again, and make described main switch S
wbetween conducting state and off state, switch, thereby can make described LED drive circuit export a constant current signal.
By the above-mentioned course of work, can draw,
Described the second time period T
2for described main switch S
win the time period of conducting state, i.e. its ON time, described very first time section T
1for S
wa time period in period time in conducting state, due to V
c2=I
2× (T
1+ T
2)/C
2=V
c1=I
1× T
1/ C
1, can draw as described the first current source I
1, the second current source I
2, the first capacitor C
1with the second capacitor C
2setting parameter good after, after described constant-current control circuit sets, described very first time section T
1with described the second time period T
2between proportionate relationship also just determined, i.e. T
1/ T
2=1/N, N has the parameter of above-mentioned current source and electric capacity to determine.In addition, can be drawn I by the above-mentioned course of work
l1and I
l3be respectively described main switch S
wa switch periods in minimum value and the maximum of inductive current, again due to inductive current I
lat main switch S
wadvancing the speed of conduction period is identical, and remembers that the desired output electric current of described LED drive circuit is I
o, described constant-current control circuit can make following equation set up in the course of the work:
Due in LED drive circuit, in each switch periods, the difference of the maximum IL3 of inductive current IL and minimum value IL1 is called the ripple value of inductive current, this value is generally a definite definite value after circuit design is good, and N, with k1 be also a definite definite value, can draw by above-mentioned formula, as long as the size of the output current Io expecting according to LED drive circuit is set the value of suitable reference voltage signal Vref, just can realize the constant current output of LED drive circuit, normally work with driving LED load.
In like manner, if in above-described embodiment, described the first state is off state, described the second state is conducting state, described the second time period T2 is that described main switch SW is in the turn-off time, as long as the value of described reference voltage signal Vref is set according to the desired output electric current of described LED drive circuit, just can in the turn-off time of described main switch SW section, control described LED drive circuit, described main switch SW is switched between conducting state and off state, thereby can make described LED drive circuit export a constant current signal.
It should be noted that, the power stage circuit of the LED drive circuit in above-mentioned illustrating is voltage-dropping type, but the disclosed constant-current control circuit of the embodiment of the present application is equally also applicable in LED drive circuit that power circuit is booster type or other type.For example, if when described LED drive circuit is booster type, the mean value of the inductive current in described LED drive circuit equals the input current Is of described LED drive circuit, owing to closing between the input current Is of described LED drive circuit and output current Io be: Io=Is (1-D), D is the duty ratio of the pwm signal of described constant-current control circuit output, as long as in the time setting the value of described reference voltage signal Vref according to the desired output electric current I o of described LED drive circuit, introducing the feedback signal of a described pwm signal sets again, for example can in the time forming described reference voltage, make described reference voltage signal is a voltage relevant to the duty ratio of described pwm signal, such setting means is easy to just can be accomplished in several ways for a person skilled in the art, therefore concrete setting means does not limit in this application.
Therefore, the constant-current control circuit that adopts the application to provide, only need to utilize the first charging circuit and the second charging circuit in the time that main open pipe switches to the first state, all to start charging, then utilize inductive current described in an inductive current sample circuit to obtain a sampled signal, and described sampled signal and a reference voltage are compared with one first comparison circuit, result is relatively for controlling the charging interval of the first charging circuit, again in order to the voltage of more described the second charging circuit of one second comparison circuit and the first charging circuit, result is relatively for controlling the charging interval of the second charging circuit, so in the time that stopping charging, described the second charging circuit make the main switch in described LED drive circuit switch to the second state by the first state, thereby control LED drive circuit and export a constant current signal.Therefore, the constant-current control circuit that the application provides need not be by the external sampling resistance LED electric current of sampling in the time realizing constant current control, effectively raise the integrated efficiency of LED drive circuit, and can be applicable to, in various types of LED drive circuits, have wide range of applications.
Fig. 3 is the structure chart of the disclosed another kind of constant-current control circuit of the embodiment of the present application.
Referring to Fig. 3, in the present embodiment, described constant-current control circuit is applied in LED drive circuit, in described LED drive circuit, the power stage circuit 02 of described LED drive circuit is booster type topological structure, is provided with main switch SW and inductance L in described power stage circuit.In the present embodiment, provided the concrete form of inductive current sample circuit 011, the first comparison circuit 012, the first charging circuit 013, the second charging circuit 014, the second comparison circuit 015 and pwm signal generation circuit 016 in described constant-current control circuit.
Described inductive current sample circuit 011 comprises ratio circuit 0111 and a transfer resistance R
1, one end that described ratio circuit 0111 is connected with described SW with described inductance L is connected, and by described transfer resistance R1 ground connection, for obtain one with the inductive current I that flows through described inductance
lproportional sample rate current I
sen, I
sen=k
0× I
l, k
0for proportionality coefficient.Sample rate current I
senby transfer resistance R
1convert a sampled voltage signal V to
sen, i.e. V
sen=I
sen* R
1=k
0× I
l× R
1, by described sampled voltage signal V
senoutput is as described inductive current I
lsampled signal.
Described the first comparison circuit 012 comprises one first comparator C omp1, and the in-phase input end of the first comparator receives a reference voltage signal V
ref, reverse input end receives described sampled voltage signal V
sen, output is exported the first comparison signal Q
1.
Described the first charging circuit 013 comprises the first current source I
1, the first capacitor C
1, the first switch S
1with the 3rd switch S
3.The first current source I
1by the 3rd switch S
3with the first capacitor C
1one end be connected, the first capacitor C
1other end ground connection, described the first switch S
1two ends respectively with described the first capacitor C
1two ends be connected.Described the first switch S
1by switch controlling signal Q
3control switch controlling signal Q
3can be for the pwm signal of described constant-current control circuit output can be also a signal of synchronizeing with described pwm signal, the 3rd switch S
3by described the first comparison signal Q
1control.
Described the first charging circuit 014 comprises the second current source I
2, the second capacitor C
2with second switch S
2.The second current source I
2with the second capacitor C
2one end be connected, the second capacitor C
2other end ground connection, described second switch S
2two ends respectively with described the second capacitor C
2two ends be connected.Described second switch S
2with described the first switch S
1on off state identical, also can be by switch controlling signal Q
3control.
Described the second comparison circuit 015 comprises the second comparator C omp2, and the input in the same way of the second comparator C omp2 is connected with the ungrounded end of described the second capacitor C 2, to receive described the second capacitor C
2on voltage V
c2, reverse input end and described the first capacitor C
1ungrounded end be connected, to receive described the first capacitor C
1on voltage V
c1, output is exported the second comparison signal Q
2.
Described pwm signal generative circuit 016 comprises a rest-set flip-flop, the set termination of described rest-set flip-flop is received one first control signal, described the first control signal can also can enter the signal of conducting state for other can trigger described main switch for external timing signal, be an external timing signal CLK in the present embodiment, in the time that the rising edge of external timing signal CLK arrives, show that external timing signal CLK is in effective status, start to trigger described main switch S
wenter conducting state; The reset terminal of described rest-set flip-flop receives described comparison signal Q
2, output output is used for controlling described main switch S
wthe pwm signal of switch motion.
In the present embodiment, described the first current source I
1electric current and the first capacitor C
1the ratio of capacitance be described the second current source I
2electric current and the second capacitor C
2the twice of ratio of capacitance, i.e. I
1/ C
1=2 × I
2/ C
2, in the present embodiment, T
1=T
2/ 2.
Fig. 4 is the working waveform figure of the disclosed constant-current control circuit of the present embodiment.
With reference to figure 4, at t
0in the moment: the rising edge of external timing signal CLK arrives, making the pwm signal saltus step of rest-set flip-flop output is high level, controls described main switch S
wenter conducting state, inductive current I
lvalue start by I
l1rise, sampled voltage signal V
senalso start to rise, and now, the first switch S
2with second switch S
2disconnect the 3rd switch S
3conducting, the first current source I
1with the second current source I
2start respectively the first capacitor C
1with the second capacitor C
2charging.Due to I
1/ C
1=2 × I
2/ C
2, the voltage V of the first capacitor C 1
c1(the solid line indicating section in Fig. 4) is than the voltage V of the second capacitor C 2
c2it is fast that (the dotted line indicating section in Fig. 4) increases.At t
1moment, inductive current I
lvalue rise to I
l2, now V
senequal V
ref, the first comparison signal Q
1when saltus step low level (in the present embodiment, the effective status of described the first comparison signal is high level, and disarmed state is low level, does not certainly limit to such definition), the 3rd switch S
3disconnect the first current source I
1stop the first capacitor C
1charging, V
c1at S
1before conducting, remain unchanged.From t
0to t
1time period be very first time section T
1, after this, the second current source I
2continue the second capacitor C
2charging, until t
2moment, V
c2=V
c1, the second comparison signal Q
2saltus step is high level, and the pwm signal saltus step of rest-set flip-flop output is low level, controls described main switch S
wenter off state, the second time period T
2finish now inductive current I
lvalue rise to I
l3, and start by I
l3decline, until the rising edge of external timing signal CLK arrives again, enter a new switch periods.
The principle that in the present embodiment, constant-current control circuit is realized constant-current control circuit is basically the same as those in the first embodiment, and no longer continues to set forth at this.This enforcement is only by setting the design parameter in the first charging circuit and the second charging circuit, by very first time section T
1with the second time period T
2ratio value be defined as 1:2, i.e. T
1/ T
2=1/2, can draw by the formula of inferring in the first embodiment, at the present embodiment, V
ref=I
s× k
0× R
1, I
sfor the input current of described LED drive circuit, the output current I of itself and LED drive circuit
obetween pass be: I
s(1-D)=I
o, the duty ratio that wherein D is described pwm signal, V
ref=I
o× k
0× R
1/ (1-D).Because circuit is after designing, k
0, R
1be definite fixed number, if according to expect output current I
osize set reference voltage signal V
refvalue time, then introduce the feedback signal of pwm signal, make reference voltage signal V
refalso relevant to the duty ratio of pwm signal, and the constant current signal that can make described LED drive circuit output meet loading demand is next, specific implementation is set reference voltage signal V
refthe circuit form of value can be various, no longer describes in detail at this.
Fig. 5 is the structure chart of disclosed another constant-current control circuit of the embodiment of the present application.
With reference to figure 5, in the constant-current control circuit application LED drive circuit in the present embodiment, described LED drive circuit is different from a upper embodiment, and its power stage circuit 02 is voltage-dropping type topological structure.Basic identical in described constant-current control circuit and a upper embodiment, different only, in the present embodiment, the receiver voltage of the input in the same way sampled signal V of the first comparator C omp1
sen, reverse input end receives reference voltage signal V
ref, and the reset terminal of rest-set flip-flop receives the first control signal, reset terminal receives the second comparison signal.
Fig. 6 is the working waveform figure of the constant-current control circuit of the present embodiment, with reference to figure 6, can know in the present embodiment, and when the first control signal is effective status, main switch S
wswitch to off state, the output current of LED drive circuit for adjusting during the off state of main switch, and in upper and embodiment, when the first control signal is effective status, main switch S
wswitch to conducting state, the output current of LED drive circuit for adjusting during the conducting state of main switch.Therefore, all identical with a upper embodiment of the control procedure of the constant-current control circuit in the present embodiment and control principle, repeat no longer in detail at this.
T in above-mentioned each embodiment
1represent described very first time section T
1duration, T
2represent described the second time period T
2duration, I
1represent described the first current source I
1size of current, I
2represent described the second current source I
2size of current, C
1represent described the first capacitor C
1capacitance, C
2represent described the second capacitor C
2capacitance.
The constant-current control circuit proposing corresponding to above-mentioned each embodiment, the application has also proposed a kind of LED drive circuit, described LED drive circuit comprises any one constant-current control circuit in power stage circuit and above-mentioned each fact Example, in described power stage circuit, be provided with main switch and inductance, described constant-current control circuit is exported a pwm signal, to control the switch motion of described main switch, make described LED drive circuit export a constant current signal.
It should be noted that, the mode of operation of described LED drive circuit can but be not limited to continuous current mode formula pattern, and the topological structure of described power stage circuit can be the topological structure of booster type, voltage-dropping type or other any type.The LED drive circuit that the application provides, in the time realizing constant current output, has control circuit simple, the characteristic that integrated level is high and output current ripple is little.
Fig. 7 is the schematic flow sheet of the disclosed a kind of constant current control method of the embodiment of the present application.
With reference to figure 7, the constant current control method that the present embodiment provides, is applied in LED drive circuit, is provided with main switch and inductance in described LED drive circuit, said method comprising the steps of:
Step 701: obtain the sampled signal that characterizes the inductive current that flows through described inductance.
Step 702: in the time that described main switch switches to the first state, start with the first electric current the first capacitor charging, the second electric current is to the second capacitor charging.
Step 703: in the time that described sampled signal equals a reference voltage signal, stop described the first capacitor charging.
Step 704: in the time that the voltage on described the second electric capacity equals the voltage on described the first electric capacity, stop described the second capacitor charging.
Step 705: control described main switch and switch to the second state by described the first state.
Wherein, will the time period of described the first capacitor charging be designated as to very first time section, the time period when to described the second capacitor charging was designated as for the second time period, and described very first time section is finished before described the second time period finishes.
Described the first state is conducting state, and described the second state is off state, and also can make described the first state is off state, and described the second state is conducting state.
The constant current control method that the present embodiment provides is applied in LED drive circuit, the output current that can make LED drive circuit output expect, normally work with driving LED load, and adopt constant-current control circuit that the constant current control method that provides of the application realizes in the time realizing constant current control without adopting the non-essential resistance inductive current of sampling, greatly improved the integrated level of LED drive circuit.
In this specification, each embodiment adopts the mode of going forward one by one to describe, and what each embodiment stressed is and the difference of other embodiment, between each embodiment same or similar part mutually referring to.
To the above-mentioned explanation of the disclosed embodiments, make professional and technical personnel in the field can realize or use the present invention.To be apparent for those skilled in the art to the multiple amendment of these embodiment, General Principle as defined herein can, in the situation that not departing from the spirit or scope of the present invention, realize in other embodiments.Therefore, the present invention will can not be restricted to these embodiment shown in this article, but will meet the widest scope consistent with principle disclosed herein and features of novelty.
Claims (12)
1. a constant-current control circuit, for LED drive circuit, is provided with main switch and inductance in described LED drive circuit, described constant-current control circuit comprises:
The first comparison circuit, for relatively one characterizing sampled signal and a reference voltage signal of the inductive current that flows through described inductance, and exports the first comparison signal;
The first charging circuit, comprises the first electric capacity, the first current source, and in very first time section, described the first current source is to described the first capacitor charging;
The second charging circuit, comprises the second electric capacity, the second current source, and within the second time period, described the second current source is to described the second capacitor charging;
The second comparison circuit, for the voltage on voltage and the second electric capacity on more described the first electric capacity, and exports the second comparison signal;
In the time that described main switch switches to the first state, described very first time section and described the second time period start to occur simultaneously, in the time that described sampled signal equals described reference voltage signal, described very first time section finishes, in the time that the voltage on described the second electric capacity equals the voltage on described the first electric capacity of section finish time described very first time, described the second time period finishes and described main switch switches to described the second state;
Described very first time section finishes before described the second time period finishes.
2. constant-current control circuit according to claim 1, is characterized in that, also comprises inductive current sample circuit, and described inductive current sample circuit is connected with one end of described inductance, for the described inductive current of sampling, and exports described sampled signal.
3. constant-current control circuit according to claim 2, it is characterized in that, also comprise pwm signal generation circuit, described pwm signal generation circuit is for generating pwm signal according to described the second comparison signal and one first control signal, switch between described the first state and described the second state to control described main switch, make described LED drive circuit export a constant current signal, in the time that described the first control signal is effective status, described main switch switches to described the first state.
4. constant-current control circuit according to claim 3, is characterized in that, described the first charging circuit also comprises the first switch, and the two ends of described the first switch are connected with the two ends of described the first electric capacity respectively;
Described the second charging circuit also comprises second switch, and the two ends of described second switch are connected with the two ends of described the second electric capacity respectively;
Described the first switch and described second switch all turn-off during described main open pipe is described the first state, conducting during described main open pipe is described the second state.
5. constant-current control circuit according to claim 4, it is characterized in that, described the first charging circuit also comprises the 3rd switch, and described the 3rd pass is connected between described the first current source and described the first electric capacity, the conducting in the time that described the first comparison signal is effective status of described the 3rd switch.
6. constant-current control circuit according to claim 5, is characterized in that, described the first comparison circuit comprises one first comparator, and described the second comparison circuit comprises one second comparator, and described pwm signal generation circuit comprises a rest-set flip-flop;
The input in the same way of described the second comparator receives the voltage on described the second electric capacity, and backward end receives the voltage on described the first electric capacity, and output is exported described the second comparison signal.
7. constant-current control circuit according to claim 6, is characterized in that, described the first state is conducting state, and described the second state is off-state.
8. constant-current control circuit according to claim 6, is characterized in that, described the first state is off-state, and described the second state is conducting state.
9. constant-current control circuit according to claim 5, is characterized in that, the in-phase input end of described the first comparator receives described reference voltage signal, and reverse input end receives described sampled signal, and output is exported described the first comparison signal;
The RESET input of described rest-set flip-flop receives described the second comparison signal, and set income termination is received described the first control signal.
10. constant-current control circuit according to claim 8, is characterized in that, the in-phase input end of described the first comparator receives described sampling, and reverse input end receives described reference voltage signal, and output is exported described the first comparison signal;
The RESET input of described rest-set flip-flop receives described the first control signal, and set income termination is received described the second comparison signal.
11. 1 kinds of LED drive circuits, comprise a power stage circuit, are provided with main switch and inductance in described power stage circuit, it is characterized in that, also comprise as the constant-current control circuit as described in any in claim 1-10,
Described constant-current control circuit is exported a pwm signal, to control the switch motion of described main switch, makes described LED drive circuit export a constant current signal.
12. 1 kinds of constant current control methods, for LED drive circuit, are provided with main switch and inductance in described LED drive circuit, described method comprises:
Obtain the sampled signal that characterizes the inductive current that flows through described inductance;
In the time that described main switch switches to the first state, start with the first electric current the first capacitor charging, the second electric current is to the second capacitor charging;
In the time that described sampled signal equals a reference voltage signal, stop described the first capacitor charging;
When voltage on described the first electric capacity in the time that the voltage on described the second electric capacity equals to stop described the first capacitor charging, stop described the second capacitor charging, and control described main switch and switch to the second state by described the first state;
To the time period of described the first capacitor charging be designated as to very first time section;
Time period when to described the second capacitor charging was designated as for the second time period;
Described very first time section finishes before described the second time period finishes.
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| CN105657899A (en) * | 2016-02-22 | 2016-06-08 | 南京矽力杰半导体技术有限公司 | Multi-circuit LED constant current driving circuit and control method thereof |
| CN107306466A (en) * | 2016-04-22 | 2017-10-31 | 美芯晟科技（北京）有限公司 | Adjusting control circuit for LED driver |
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