CN101505558B - Light emission element driving circuit having compensation mechanism - Google Patents

Abstract

A luminous element drive circuit with a compensation mechanism is used for driving at least one luminous element and comprises a switching element, a comparator, a drive module and a timing circuit, wherein the switching element is used for controlling drive current flowing through the luminous element according to the conduction or unconduction of a control signal; the comparator generates a comparison result according to a reference voltage and a feedback voltage corresponding to the drive current; the drive module generates the control signal according to the comparison result; the timing circuit is used for controlling the drive module to conduct the switching element after the switching element is not conducted for a preset time; and a compensation module is used for detecting the conduction time of the switching element and delay time of corresponding change generated by the control signal when the feedback voltage reaches a reference voltage value, and adjusting the reference voltage according to the conduction time and the delay time.

Description

Light emitting element driving circuit with compensation mechanism

Technical field

The present invention relates to a kind of light emitting element driving circuit, particularly relate to a kind of light emitting element driving circuit with compensation mechanism.

Background technology

At more early stage light-emitting component (for example: light-emitting diode) in the drive circuit, all be to utilize pulse width modulation circuit to control a switch element, and utilize the size of current of this switch element control flows through light-emitting component.Utilize again a comparator more therewith a feedback voltage of the proportional relation of electric current decide and will increase or reduce electric current, this technology is current peak (peak-current) control technology of generally knowing.But such structure has many shortcomings.For instance, the current ripple under this structure (currentripple) can change along with the difference of input voltage, and the input voltage of light-emitting component is alternating voltage usually, therefore can cause the electric current accuracy not good, and then has influence on the durability of light-emitting component.And, because pulse width modulation circuit is the mode of operation of fixed frequency, therefore can make circuit have relatively poor electromagnetic protection ability.Also might close in the ideal of switch element in addition, (that is: not conducting) during time no show still, pulse width modulation circuit just makes the switch element conducting, thereby causes the phenomenon of vibration.

Fig. 1 shows the circuit diagram of the light emitting element driving circuit 100 of prior art, and it has improved above-mentioned light emitting element driving circuit.As shown in Figure 1, light emitting element driving circuit 100 comprises a comparator 101, a driver module 103 and a timing circuit 105.Comparator 101 is feedback voltage V relatively _Fb(it is to produce with drive current I according to resistance 108) and reference voltage V _Ref, and making driver module 103 outputs one control signal VG with control switch element 107, control flows is through the electric current I of light-emitting component 109 and inductance 111 by this.Different with above-mentioned light emitting element driving circuit is; Light emitting element driving circuit 100 also comprises a timing circuit 105; Its meeting control and driving module 103; Make switch element 107 after one scheduled time of not conducting, recover conducting, just in order to adjust the length of this scheduled time, this technology is fixing not ON time (constant off-time) control technology of generally knowing to resistance 106.

The benefit of doing like this is that because ON time is not fixed, current ripple can not change along with the difference of input voltage, therefore can not cause the not good situation of electric current accuracy.And the operating frequency of pulse width modulation circuit is unfixing, therefore can make circuit have electromagnetic protection ability preferably.In addition, because the discharge slope fixes, thus can avoid the desirable shut-in time no show still of above-mentioned switch element the time, just make the switch element conducting, thereby cause the problem of vibration.

Yet such structure but has other problem to exist.Fig. 2 shows the electric current-time relationship of the light emitting element driving circuit of prior art.As shown in Figure 2, the maximum of electric current I should be limited at I originally _SU, but, work as feedback voltage V because circuit itself has nonideal time of delay _FbReach reference voltage V _RefThe time, to control signal VG by the high potential transition be electronegative potential have one time of delay t _d, therefore actual electric current I can arrive I _Max, and shut-in time t _OffFor fixing, therefore can't offset the excessive effect of electric current, thereby cause the instability of electric current accuracy.If input voltage V _InBig more, then this situation is obvious more.

Summary of the invention

Embodiments of the invention have disclosed a kind of light emitting element driving circuit with compensation mechanism, and in order to drive at least one light-emitting component, light emitting element driving circuit comprises a switch element, a comparator, a driver module and a timing circuit.Switch element is controlled by a control signal, the flow through size of drive current of this light-emitting component of the duty ratio of this control signal decision.This comparator produces a comparative result according to a reference voltage and to a feedback voltage that should drive current.This driver module produces this control signal according to this comparative result.This timing circuit is controlled this driver module and is made this switch element conducting in order to after this one scheduled time of not conducting of switch element.When this compensating module reached this reference voltage level in order to the ON time that detects this switch element and this feedback voltage, this control signal produced the time of delay of corresponding change, and according to adjusting this ON time and this time of delay reference voltage.

By the above embodiments, because the not ON time of this switch element is fixed, current ripple can not change along with the difference of input voltage, therefore can not cause the not good situation of electric current accuracy.And the operating frequency of pulse width modulation circuit is unfixing, therefore can make circuit have electromagnetic protection ability preferably.In addition, because the discharge slope fixes, thus can avoid the desirable shut-in time no show still of above-mentioned switch element the time, just make the switch element conducting, thereby cause the problem of vibration.And, more can compensate because of unfavorable circuit delay time and cause the not good phenomenon of current accuracy.

Description of drawings

Fig. 1 shows the circuit diagram of the light emitting element driving circuit of prior art.

Fig. 2 shows the electric current-time relationship of the light emitting element driving circuit of prior art.

Fig. 3 (a) shows the circuit diagram according to the light emitting element driving circuit of preferred embodiment of the present invention.

Electric current-the time relationship of the light emitting element driving circuit of the present invention that Fig. 3 (b) shows.

Fig. 4 shows the detailed circuit diagram according to the light emitting element driving circuit of preferred embodiment of the present invention.

The example that Fig. 5 shows the ON time detector shown in Fig. 4 with and the action sketch map.

Fig. 6 show shown in Fig. 4 time of delay detector an example with and the action sketch map.

Fig. 7 shows the circuit diagram according to another light emitting element driving circuit of preferred embodiment of the present invention.

The reference numeral explanation

100,300 light emitting element driving circuits

301 switch elements

109,302 light-emitting components

101,303 sluggish formula comparators

111,304 inductance

103,305 driver modules

105,307 timing circuits

107 switch elements

The 305a trigger

The 305b driver

309 compensating modules

106,108,311,313 resistance

315,317 contacts

401 ON time detectors

403 time of delay detector

405 arithmetic units

501,601 current sources

503,603 switch modules

504,506,604,606 switches

505,605 electric capacity

507,607 peak holding circuits.

Embodiment

Fig. 3 (a) shows the sketch map according to the light emitting element driving circuit of preferred embodiment of the present invention.Shown in Fig. 3 (a); Light emitting element driving circuit 300 is in order to driven light-emitting element 302 (that is a drive current I being provided to light-emitting component 302), comprises a switch element 301, a comparator 303, a driver module 305, a timing circuit 307 and a compensating module 309.Switch element 301 is a power transistor (power transistor) at present embodiment.Driver module 305 output one control signal VG decides the conducting or the not conducting of switch element 301, with the drive current I of control flows through light-emitting component 302, so the duty ratio of control signal VG promptly determine the to flow through size of drive current of this light-emitting component.The electric current of resistance 311 of flowing through produces a feedback voltage V _FB, because of the electric current of the resistance 311 of flowing through is proportional to drive current I, so feedback voltage V _FBAlso be proportional to drive current I.

Comparator 303 is in order to according to a reference voltage V _RefAnd feedback voltage V _FBProduce a comparative result (output signal), driver module 305 is in order to produce control signal VG according to comparative result.In this embodiment; Driver module 305 comprises a trigger 305a and a driver 305b; But be not that the output signal of trigger 305a increases driving force is enough to pull switch element 301 with generation control signal VG via driver 305b in order to qualification the present invention.

After switch element 301 conductings, along with the increase gradually of drive current I, feedback voltage V _FBAlso increase gradually, work as feedback voltage V _FBReach reference voltage V _RefThe time; The output signal of comparator 303 is a logic high potential by the logic low potential transition; And the replacement input R of triggering trigger 305a; The output signal of trigger 305a is a logic low potential by the logic high potential transition, control signal VG thereby be logic low potential by the logic high potential transition, switch element 301 thereby not conducting; Work as feedback voltage V _FBReach reference voltage V _RefThe time; The output signalisation timing circuit 307 of the logic high potential of comparator 303 begins counting; After counting up to a scheduled time; Timing circuit 307 outputs | the set input S of the output signal triggering trigger 305a of logic high potential, control signal VG is a logic high potential by the logic low potential transition, switch element 301 thereby conducting again.Resistance 313 is in order to adjust the length of this scheduled time.

Driver module 305, comparator 303 and timing circuit 307 can be regarded a control circuit together, produce control signal, are positioned at conducting state or not on-state with control switch element 301.

And compensating module 309 is in order to the ON time t of sense switch element 301 _OnAnd t time of delay that is caused by comparator 303 and driver module 305 _d(that is work as feedback voltage V _FbReach reference voltage V _RefThe time, to control signal VG be the time of delay of electronegative potential by the high potential transition), and according to ON time t _OnWith t time of delay _dProportionate relationship calculate | the reference voltage V after the compensation _Csref, to upgrade reference voltage V _Ref, use and reduce t time of delay _dInfluence to current accuracy.

Please refer to Fig. 3 (b), drive current I expects that originally the value that reaches is I _SU, but because of t time of delay _dRelation, the value that can cause drive current I is excessive and reach I _MaxTherefore if the reference voltage level of comparator 303 is turned down, expect that then the current value that reaches can be lowered into I _SU', identical ground is because of t time of delay _dRelation, the value that also can cause drive current I is excessive and reach I _Max', make the value of ISU equal I by this _Max' value, to eliminate t time of delay _dInfluence.The computational process of reference voltage has been described in formula (1)-(3):

${\mathrm{\Δ\; I}}_{\mathrm{Ripple}}=I_{\mathrm{Max}}-I_{\mathrm{Min}}=\frac{V_{\mathrm{Leds}}}{L}{t}_{\mathrm{Off}}$ Formula 1

$\frac{V_{\mathrm{Csref}}}{R_{\mathrm{Sns}}}=\frac{V_{\mathrm{Ref}}}{R_{\mathrm{Sns}}}-t_d\×\frac{{\mathrm{CR}}_1{I}_{\mathrm{Mean}}}{t_{\mathrm{On}}}$ Formula 2

$V_{\mathrm{Csref}}=V_{\mathrm{Ref}}-\frac{V_{\mathrm{Ref}}}{{\mathrm{CR}}_2{I}_{\mathrm{Mean}}}\×t_d\×\frac{{\mathrm{CR}}_1{I}_{\mathrm{Mean}}}{t_{\mathrm{On}}}$ Formula 3

Wherein, formula (1) is represented current ripple, V _LedsBe the voltage on the light-emitting component 302 among Fig. 3, and L is the value of inductance 304, and t _OffIt is the not ON time of switch element 301.In formula (2), V _RefSystem is the preceding initial reference magnitude of voltage of compensation not, V _CsrefBe the reference voltage level of compensation back adjustment, R _SnsBe the value of resistance 311, I _MeanBe average current value (=(I _Max+ I _Min)/2).CR ₁Be with the first relevant reference value of current ripple, for instance, if current ripple estimated for+/-20%, CR then ₁Be 0.4, if current ripple estimated for+/-30%, CR then ₁Be 0.6, by that analogy, and by formula (2) can push away formula (3).In formula (3), CR ₂Be with the second relevant reference value of current ripple, for instance, if current ripple estimated for+/-20%, CR then ₂Be 1.2, if current ripple estimated for+/-30%, CR then ₂Be 1.3, by that analogy.

At this with V _Ref=0.25V, current ripple estimated for+/-20% for example, then above-mentioned formula (1), (2) and (3) then become:

${\mathrm{\Δ\; I}}_{\mathrm{Ripple}}=I_{\mathrm{Max}}-I_{\mathrm{Min}}=\frac{V_{\mathrm{Leds}}}{L}{t}_{\mathrm{Off}}$ Formula 1

$\frac{V_{\mathrm{Csref}}}{R_{\mathrm{Sns}}}=\frac{0.25}{R_{\mathrm{Sns}}}-t_d\×\frac{{0.4I}_{\mathrm{Mean}}}{t_{\mathrm{On}}}$ Formula 2

$V_{\mathrm{csref}}=0.25-\frac{0.25}{{1.2I}_{\mathrm{mean}}}\×t_d\×\frac{{0.4I}_{\mathrm{mean}}}{t_{\mathrm{on}}}$

$=0.25-0.0833\×t_d\×\frac{1}{t_{\mathrm{On}}}$ Formula 3

Can know V by formula (3) _CsrefBe and ON time t _OnWith t time of delay _dRatio relevant, therefore only must record ON time t _OnWith t time of delay _dRatio just can try to achieve V _Csref, must not consider other variable.

Fig. 4 shows the detailed circuit diagram of the light emitting element driving circuit of the preferred embodiment according to the present invention.As shown in Figure 4, compensating module 309 comprise an ON time detector 401, one time of delay detector 403 an and arithmetic unit 405.ON time detector 401 is in order to producing an ON time parameter, time of delay detector 403 in order to produce a delay time parameter, arithmetic unit 405 is in order to produce reference voltage V according to ON time parameter and delay time parameter _Ref

The example that Fig. 5 shows the ON time detector shown in Fig. 4 with and the action sketch map.In this example, ON time detector 401, it comprises a current source 501, a switch module 503, an electric capacity 505 and a peak holding circuit 507.Current source 501 is in order to provide a scheduled current I _OnSwitch module 503 makes electric capacity 505 according to scheduled current I according to control signal VG _OnCharge or discharge are to produce an ON time parameter signal S _TonParticularly, when switch element 301 conductings, control signal VG can make switch 504 conductings, and by this to electric capacity 505 charging, and during switch element 301 not conductings, control signal VG can make switch 506 conductings, by this to electric capacity 505 discharges.Peak holding circuit 507 sampling ON time parameter signal S _Ton(in this example for getting its peak value) is to produce the ON time parameter.ON time t _OnCan push away by following formula (4):

$C_{\mathrm{On}}\×V_{\mathrm{En}}=I_{\mathrm{On}}\×t_{\mathrm{On}}\→t_{\mathrm{On}}=\frac{C_{\mathrm{On}}\×V_{\mathrm{En}}}{I_{\mathrm{On}}}$ Formula 4

Wherein, C _OnBe the value of electric capacity 505, V _EnBe ON time parameter signal S _TonCrest voltage (that is ON time parameter), by this formula, just can try to achieve ON time t _On

Fig. 6 show shown in Fig. 4 time of delay detector an example with and the action sketch map.In this example, time of delay, detector 403, and it comprises a current source 601, a switch module 603, an electric capacity 605 and a peak holding circuit 607.Because manner of execution is identical with circuit shown in Figure 5, so repeat no more at this.Please again with reference to figure 3 (a), in this example, because the direct control switch module 603 of the time difference at contact 315 and 317 places, so time of delay, detector 403 must comprise a delay function signal generating circuit (not shown) in addition, according to t time of delay _dProduce a delay function signal f (t _d), in order to control switch module 603.Delay function signal f (t _d) can produce by following steps: compare feedback voltage V _FBWith reference voltage V _Ref, get a comparative result; And, comparative result and control signal VG are carried out mutual exclusion or (exclusive OR) computing, just can produce delay function signal f (t _d).

Time of delay t _dCan push away by following formula (5):

$C_d\×V_{\mathrm{End}}=I_d\×t_d\→t_d=\frac{C_d\×V_{\mathrm{End}}}{I_d}$ Formula 5

Wherein, C _dBe the value of electric capacity 605, V _EndBe delay time parameter signal S _TdCrest voltage (that is delay time parameter), by formula (3) (4) (5), just can try to achieve the reference voltage level V after the compensation _Csref, shown in formula (6).

$V_{\mathrm{Csref}}=0.25-0.0833\×\frac{V_{\mathrm{End}}}{V_{\mathrm{En}}}\×\frac{C_d}{C_{\mathrm{On}}}\frac{I_{\mathrm{On}}}{I_d}$ Formula 6

Arithmetic unit 405 produces the reference voltage level after compensating according to the relevant parameter of formula (6).

Compensating module 309 can directly detect feedback voltage V among Fig. 3 (a) _FB, the substitute is the comparative result of direct detection comparator 303, as shown in Figure 7.Possibly only cover the signal delay time of driver module 305 signal delay time that Fig. 7 measures, and lacked the signal delay time of comparator 303.If less than the signal delay time of driver module 305, then can directly ignore the signal delay time of comparator 303 very much, with just directly treating as t time of delay the signal delay time of driver module 305 _dIf can not ignore the signal delay time of comparator 303, then can be added a deviant (offset) signal delay time of driver module 305, treat as t time of delay that is wanted _d

It is noted that Fig. 5 and structure shown in Figure 6 be only in order to for example, is not in order to limiting the present invention, and other structure that can reach identical effect also should be within scope of the present invention.In addition, according to the above embodiments, can obtain corresponding light emitting element driving method, its step can be summarized as follows: the feedback voltage according to a drive current of a reference voltage and corresponding this light-emitting component of flowing through produces a comparative result; Produce a control signal according to comparative result; Come conducting or not conducting one switch element with the drive current of control flows according to control signal through light-emitting component; If after one scheduled time of not conducting of switch element, make the switch element conducting; And the ON time of sense switch element and feedback voltage be when reaching reference voltage level, and control signal produces the time of delay of corresponding change, and according to ON time with adjust this reference voltage time of delay.The detailed features of the method details in the foregoing description, so repeat no more at this.

By the above embodiments, can have following advantage: ON time is not fixed, and current ripple can not change along with the difference of input voltage, therefore can not cause the not good situation of electric current accuracy; The operating frequency of pulse width modulation circuit is unfixing, therefore can make circuit have electromagnetic protection ability preferably; The discharge slope is fixed, thus can avoid the desirable shut-in time no show still of above-mentioned switch element the time, just make the switch element conducting, thereby cause the problem of vibration; Can compensate because of unfavorable circuit delay time and cause the not good phenomenon of current accuracy; The reference voltage that is provided is the proportionate relationship of electric capacity and electric current, does not therefore have other variables; Compensation mechanism must extra increase pin, can simplify component number and design.

The above is merely preferred embodiment of the present invention, and all equalizations of doing according to claim of the present invention change and modify, and all should belong to covering scope of the present invention.

Claims (12)

1. light emitting element driving circuit with compensation mechanism in order to drive at least one light-emitting component, comprises:

One switch element is controlled by a control signal, in order to the drive current of control flows through this light-emitting component;

One comparator is in order to produce a comparative result according to a reference voltage and to a feedback voltage that should drive current;

One driver module is in order to produce this control signal according to this comparative result;

One timing circuit in order to after this one scheduled time of not conducting of switch element, is controlled this driver module and is made this switch element conducting; And

One compensating module, when reaching this reference voltage level in order to the ON time that detects this switch element and this feedback voltage, this control signal produces the time of delay of corresponding change, and according to adjusting this ON time and this time of delay this reference voltage.

2. the light emitting element driving circuit with compensation mechanism as claimed in claim 1, wherein, this compensating module is according to this ON time and this reference voltage of the proportionate relationship of this time of delay adjustment.

3. the light emitting element driving circuit with compensation mechanism as claimed in claim 1, wherein, this compensating module comprises:

One ON time detector is in order to produce an ON time parameter;

One time of delay detector, in order to produce a delay time parameter; And

One arithmetic unit is in order to adjust this reference voltage according to this ON time parameter and this delay time parameter.

4. the light emitting element driving circuit with compensation mechanism as claimed in claim 3, wherein, this ON time detector comprises:

One current source is in order to provide a scheduled current;

One switch module is coupled to this current source;

One electric capacity is coupled to this switch module; And

One peak holding circuit;

Wherein, this switch module makes this electric capacity charge or discharge according to this control signal, and producing an ON time parameter signal, and this this ON time parameter signal of peak holding circuit sampling is to produce this ON time parameter.

5. the light emitting element driving circuit with compensation mechanism as claimed in claim 3, wherein, this, detector comprised time of delay:

One delay function signal generating circuit is in order to according to producing a delay function signal this time of delay;

One current source is in order to provide a scheduled current;

One switch module is coupled to this current source;

One electric capacity is coupled to this switch module; And

One peak holding circuit;

Wherein, this switch module makes this electric capacity charge or discharge according to this delay function signal, and producing a delay time parameter signal, and this this delay time parameter signal of peak holding circuit sampling is to produce this delay time parameter.

6. the light emitting element driving circuit with compensation mechanism as claimed in claim 1, wherein, this switch element is a power transistor.

7. the light emitting element driving circuit with compensation mechanism as claimed in claim 1, wherein, this light-emitting component includes at least one light-emitting diode.

8. the light emitting element driving circuit with compensation mechanism as claimed in claim 1, wherein, this driver module comprises:

One trigger, when this feedback voltage reached this reference voltage level, this comparative result made the logic current potential transition of this trigger output signal, makes this not conducting of switch element; After this one scheduled time of not conducting of switch element, this timing circuit makes the logic current potential transition of this trigger output signal, with this switch element of conducting; And

One driver produces this control signal in order to the output signal according to this trigger.

9. light emitting element driving method with compensation mechanism in order to drive at least one light-emitting component, comprises:

A feedback voltage that compares a drive current of a reference voltage and corresponding this light-emitting component of flowing through is to produce a comparative result;

Produce a control signal according to this comparative result;

Come conducting or not conducting one switch element according to this control signal, to control this drive current;

After this one scheduled time of not conducting of switch element, make this switch element conducting; And

When ON time and this feedback voltage that detects this switch element reached this reference voltage level, this control signal produced the time of delay of corresponding change, and according to adjusting this ON time and this time of delay this reference voltage.

10. the light emitting element driving method with compensation mechanism as claimed in claim 9, wherein, the step system of this this reference voltage of adjustment is according to this ON time and this reference voltage of the proportionate relationship of this time of delay adjustment.

11. the light emitting element driving method with compensation mechanism as claimed in claim 9, wherein, the step system of this this reference voltage of adjustment is according to an ON time parameter and this reference voltage of delay time parameter adjustment.

12. the light emitting element driving circuit with compensation mechanism in order to drive at least one light-emitting component, comprises:

One switch element is controlled by a control signal, can be positioned at a conducting state and a not on-state, in order to the drive current of control flows through this light-emitting component;

One control circuit in order to according to a reference voltage and to a feedback voltage that should drive current, produces this control signal; And

One compensating module; In order to detect the ON time that this switch element is positioned at this conducting state; And this feedback voltage is when reaching this reference voltage level, and this control signal produces the time of delay of corresponding change, and according to adjusting this ON time and this time of delay this reference voltage.

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