CN104470030B - The control circuit of light emitting diode - Google Patents
The control circuit of light emitting diode Download PDFInfo
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- CN104470030B CN104470030B CN201310420472.8A CN201310420472A CN104470030B CN 104470030 B CN104470030 B CN 104470030B CN 201310420472 A CN201310420472 A CN 201310420472A CN 104470030 B CN104470030 B CN 104470030B
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Abstract
Embodiments of the invention disclose a kind of control circuit to light emitting diode, may be used to control the light modulation of at least one LED strip.This adjusting control circuit includes a current driving circuit, a pulse-width modulation circuit, a feedback circuit and one from coupling circuit.This current driving circuit can optionally make one to drive a current through this LED strip according to a dim signal.This dim signal definable one light-emitting period and a non-luminous period.This pulse-width modulation circuit can produce a pulse-width signal, and it controls a power switch, sets up a driving voltage with the power end in this LED strip.This pulse-width signal produces according to a thermal compensation signal.This feedback circuit, according to a back voltage of this LED strip, can drive a compensating electric capacity, sets up this thermal compensation signal thereon.This feedback circuit should be made not drive this compensating electric capacity from coupling circuit after this light-emitting period starts the pressure period.
Description
Technical field
The present invention relates to the control circuit of light emitting diode.
Background technology
Good luminous efficiency, the component size simplified and permanent component life are so that light emitting diode is extensively shone
Bright or backlight industry is adopted.For example, the backlight in computer or telescreen, great majority are carried on the back from traditional CCFL
Optical module, is converted into LED light module.
Fig. 1 shows the existing LED driving circuit 10 that can be used in backlight module, in order to drive four to light
Diode string S1-S4.12 input power V of booster (booster)IN, rise and be pressed into driving power supply VOUT.Current control circuit
CD1-CD4 dominates driving current I1 flowing through light emitting diode string S1-S4 respectivelyLED-I4LED.LED controller 14 control electric current control
Circuit CD1-CD4 processed and the operation of booster 12.
Fig. 2 existing LED controller 14 of citing.Minimum voltage generator 20 is according to back voltage V1FB-V4FBIn minimum
Value is producing minimum back voltage VFBMIN.Back voltage V1FB-V4FBIn feedback end FB1-FB4 for light emitting diode string S1-S4
Voltage.Transducer 22 is according to minimum back voltage VFBMINWith reference voltage VREFDifference come to drive compensate end COM, to compensate electricity
Hold 23 discharge and recharges, produce offset voltage V on compensating end COMCOM.Pulse-width modulation circuit 24 is according to offset voltage VCOMTo produce control
The pulse-width signal S of power switch 28 processedDRV.Briefly, minimum voltage generator 20, transducer 22, pulse-width modulation circuit
24th, booster 12 and the such combination of light emitting diode string S1-S4, can be by minimum back voltage VFBMINAbout stablize in ginseng
Examine voltage VREF.
The current driving circuit CC1-CC4 corresponding current control circuit CD1-CD4 controlling in Fig. 1 respectively.Will be described below
The operation of current driving circuit CC1 and principle, can analogize as other current driving circuits and learn, be not repeated.Electric current
Drive circuit CC1 includes an operational amplifier 30, and its framework can make current detection voltage V1CSAbout it is stable at voltage VCSSET.
Voltage VCSSETIt is probably 0V or predeterminated voltage VCSON, by dim signal SDIMDetermine.Because current detection voltage V1CSCorresponding
Driving current I1LED, so current driving circuit CC1 can stabilized driving electric current I1LED.
Dim signal SDIMCan be used to adjust the average luminescence brightness of light emitting diode string S1-S4.Dim signal SDIMCan
To be a pulse-width signal.As dim signal SDIMFor in logic 1 when, LED controller 14 makes minimum back voltage VFBMINGreatly
About stablize in reference voltage VREF, and driving current I1LED-I4LEDStablize in predeterminated voltage VCSON, therefore light emitting diode string S1-
S4 stabilized illumination.As dim signal SDIMFor in logic 0 when, the fixing power switch closed in booster 12 of LED controller 14
28, and driving current I1LED-I4LEDStable about 0A, light emitting diode string S1-S4 do not light.Dim signal S defined belowDIMFor
In logic 1 when, be light-emitting period (Dimming-ON time) TDIM-ON；Contrary, dim signal SDIMFor in logic 0 when,
For non-luminous period (Dimming-OFF time) TDIM-OFF.Dim signal SDIMWorking cycle (duty cycle), that is,
Light-emitting period TDIM-ONRatio shared by dimming cycle, about means the brightness of light emitting diode string S1-S4.Light modulation is linear
The relation of the working cycle to dim signal for the brightness of the light source that degree (dimming linearity) refers to.For example, perfectly
The light modulation linearity is it is meant that dim signal SDIMThe working cycle fairly linear brightness being proportional to light emitting diode string S1-S4.
How to reach the good light modulation linearity, be the target that industry is pursued.
In this specification, there is identical numbered elements or device, for having identical or similar functions, structure or spy
The element of property or device, those skilled in the art can learn according to the teaching of this specification or deduce, but not necessarily completely
Identical.For succinct reason, will not repeat specification.
Content of the invention
Embodiments of the invention disclose a kind of control circuit to light emitting diode, may be used to control at least one LED strip
Light modulation.This adjusting control circuit includes a current driving circuit, a pulse-width modulation circuit, a feedback circuit and from coupling
Circuit.This current driving circuit can optionally make one to drive a current through this LED strip according to a dim signal.This light modulation
Signal definable one light-emitting period and a non-luminous period.This pulse-width modulation circuit can produce a pulse-width signal, and it is controlled
Make a power switch, a driving voltage is set up with the power end in this LED strip.This pulse-width signal is according to a thermal compensation signal
And produce.This feedback circuit, according to a back voltage of this LED strip, can drive a compensating electric capacity, sets up this compensation letter thereon
Number.This feedback circuit should be made not drive this compensating electric capacity from coupling circuit after this light-emitting period starts the pressure period.
Brief description
Fig. 1 shows the existing LED driving circuit that can be used in backlight module.
Fig. 2 existing LED controller of citing.
Fig. 3 show Fig. 1 and Fig. 2 prior art in fact it could happen that signal waveform.
The LED controller that Fig. 4 citing is implemented according to the present invention.
When Fig. 5 shows the LED controller of LED controller 60 replacement Fig. 1, the signal waveform being likely to occur.
Fig. 6 shows a kind of embodiment of transducer.
Another LED controller that Fig. 7 citing is implemented according to the present invention.
When Fig. 8 shows the LED controller of LED controller 80 replacement Fig. 1, the signal waveform being likely to occur.
Reference numeral explanation
10 LED driving circuit
12 boosters
14 LED controllers
20 minimum voltage generators
22 transducers
23 compensating electric capacities
24 pulse-width modulation circuits
28 power switch
30 operational amplifiers
60 LED controllers
62 from coupling circuit
64 transducers
66 pulse generators
68 switches
70 transducers
80 LED controllers
82 from coupling circuit
84 MAXIMUM SELECTION devices
86 comparators
88 gates
CC1-CC4 current driving circuit
CD1-CD4 current control circuit
COM compensates end
DRV drive end
EN enable end
FB1-FB4 feedback end
GAT1-GAT4 control end
I1LED-I4LEDDriving current
S1-S4 light emitting diode string
SDIMDim signal
SDRVPulse-width signal
SENEnable signal
SPLSPulse
t0、t1、t2Time point
TDIM-OFFNon-luminous period
TDIM-ONLight-emitting period
TFORCEForce the period
V1CS-V4CSCurrent detection voltage
V1FB-V4FBBack voltage
V1GAT-V4GATControl voltage
VCOMOffset voltage
VCOMONSteady state voltage value
VCSONPredeterminated voltage
VCSSETVoltage
VCS-OKReference voltage
VFBMINMinimum back voltage
VINInput power
VOUTDriving power supply
VREFReference voltage
Specific embodiment
Fig. 3 show Fig. 1 and Fig. 2 prior art in fact it could happen that signal waveform.In figure 3, from top to bottom, it is sequentially
Dim signal SDIM, minimum back voltage VFBMIN, offset voltage VCOM, current driving circuit CC1 control end GAT1 control
Voltage V1GAT, current detection voltage V1CS, and pulse-width signal SDRV.
Light-emitting period TDIM-ONIf too short, may be because of the limited driving force of current driving circuit CC1 so that Fig. 1
The light modulation linearity be deteriorated, or light emitting diode string S1-S4 produce flicker phenomenon.
Refer to Fig. 3.In the prior art, non-luminous period light TDIM-OFFWhen, offset voltage VCOMCan maintain previously
Magnitude of voltage V at the end of light-emitting periodCOMON, and current detection voltage V1CSIt is about 0V, such as time point t in Fig. 30Before
Non-luminous period TDIM-OFFShown.Now, minimum back voltage VFBMINBig appointment is equal to driving power supply VOUT, its value may be up to
Some tens of volts.
In time point t0, dim signal SDIMChange into 1 by 0, light-emitting period TDIM-ONStart.Operational amplifier 30 starts to draw high
Control voltage V1GATIt is desirable to by current detection voltage V1CSQuickly move predeterminated voltage V toCSON.However, the electricity of control end GAT1
Capacitive load, because the presence of external power transistor, may be suitable big, so result in control voltage V1GATOn slow
Rise.When control voltage V1GATWhen to a certain extent, current detection voltage V1CSJust start lentamente toward predeterminated voltage VCSONApproach,
Namely driving current I1LEDGradually toward light-emitting period TDIM-ONSteady-state current value approach.In one embodiment, predeterminated voltage
VCSONIt is about 0.4V.
With driving current I1LEDIt is gradually increasing, minimum back voltage VFBMINGradually decline.But, in time point t0
When, as the transducer 22 of feedback circuit in Fig. 2, find minimum back voltage VFBMINExceed reference voltage VREF, so transducer
22 rapidly discharging compensation electric capacity 23, drag down offset voltage VCOM.Low offset voltage VCOMThe pulsewidth producing the little working cycle is adjusted
Signal S processedDRV, such as time point t0To time point t1Period shown in.
Time point t1Start, minimum back voltage VFBMINDrop to less than reference voltage VREF, so offset voltage VCOMIn
Rise toward steady state voltage value V during light-emitting periodCOMONApproach.
Time point t2, light-emitting period TDIM-ONTerminate, non-luminous period TDIM-OFFStart.From time point t1To time point t2's
Period is it is found that light-emitting period TDIM-ONIn, minimum back voltage VFBMINSteady-state value be reference voltage VREF, current detecting electricity
Pressure V1CSSteady-state value be predeterminated voltage VCSON.Predeterminated voltage VCSONCorresponding driving current I1LED-I4LEDA steady state operation value.
From time point t0To t1Start periods it is found that offset voltage VCOMFar below steady state voltage value VCOMON.So
In this start periods, the electrical power that booster 12 is transmitted, will be far below light-emitting period TDIM-ONIn value when stablizing.Not enough
Electrical power will lead to current detection voltage V1CSSuitable slow of the speed that rises is so that current detection voltage V1CSFrom the beginning of 0V
And it is stabilized to predeterminated voltage VCSONThe required rise time significantly increases.This means light-emitting period TDIM-ONWhen extremely short
Wait, the LED driving circuit 10 of Fig. 1 will have the very poor light modulation linearity.And, light-emitting period TDIM-ONWhen short,
The light emitting diode string S1-S4 of Fig. 1 is easy to have the phenomenon of flicker.
The LED controller 60 that Fig. 4 citing is implemented according to the present invention.Although to control four light-emitting diodes in this specification
Pipe string S1-S4 is as embodiment, but the invention is not restricted to this.Some only control single luminous two according to institute of the present invention embodiment
Pole pipe string, other embodiments can control the light emitting diode string more than more than four.Control with the LED in Fig. 2 in LED controller 60
Device 14 identical part processed, is that existing personage will appreciate that, for succinct reason, is not repeated.
LED controller 60 is different from the LED controller 14 in Fig. 2, has from coupling (decoupling) circuit 62, its control
The enable end EN of transducer 64 processed.From coupling circuit 62 according to dim signal SDIMTo produce enable signal SEN.As enable signal SEN
For in logic 1 when, transducer 64 is according to minimum back voltage VFBMINWith reference voltage VREFDifference driving compensating electric capacity 23；
As enable signal SENFor in logic 0 when, transducer 64 is output as high impedance, compensates offset voltage V on the COM of endCOMSubstantially
Enable signal S can be maintainedENSwitch to the value before 0.
In one embodiment, pulse generator 66 and a gate of a rising edge triggering is included from coupling circuit 62.
Pulse generator 66 is in dim signal SDIMRising edge when occurring, produce a pulse SPLS, in order to define a pressure period TFORCE.
In the fig. 4 embodiment, the pressure period T being defined from coupling circuit 62FORCEThere is set time length.For example, this
Individual set time length can be 10 fixing microseconds, or two pulse-width signal SDRVSwitch periods (switch
cycle time).In non-luminous period TDIM-OFFAnd force period TFORCE, make enable signal S from coupling circuit 62ENFor in logic
0；And forcing period TFORCEOutside light-emitting period TDIM-ONIn, enable signal SENFor 1 in logic.
When Fig. 5 shows the LED controller 14 of LED controller 60 replacement Fig. 1, the signal waveform being likely to occur.By upper and
Under, it is sequentially dim signal SDIM, minimum back voltage VFBMIN, pulse SPLS, offset voltage VCOM, control voltage V1GAT, electric current inspection
Survey voltage V1CS, and pulse-width signal SDRV.
In Figure 5, light-emitting period TDIM-ONPressure period T after beginningFORCEInterior, transducer 64 does not drive compensating electric capacity 23,
So offset voltage VCOMAbout still maintain a front light-emitting period TDIM-ONAt the end of steady state voltage value VCOMON.This is with existing
Technology is had to have sizable difference.In Fig. 3 of prior art, time point t0To t1Start periods, offset voltage VCOMIt is fast
The minimizing of speed is so that be far below steady state voltage value VCOMON.Therefore, in the pressure period T of Fig. 5FORCEInterior, offset voltage VCOMWill
Make pulse-width signal SDRVThere is sizable working cycle, also make the electrical power that booster 12 is transmitted, when being exactly about luminous
Section TDIM-ONIn value required when stablizing.Because forcing period TFORCEIn, booster 12 provides for light emitting diode string
The electrical power of S1-S4 stabilized illumination, therefore it is desired that, current detection voltage V1CSAnd minimum back voltage VFBMINWill
Fastish approach its stationary value, be predeterminated voltage V respectivelyCSONWith reference voltage VREF, as shown in Figure 5.
Forcing period TFORCEAfter end, enable signal SENFor 1 in logic, so transducer 64 will be according to minimum time
Feedthrough voltage VFBMINWith reference voltage VREFDifference driving compensating electric capacity 23, until light-emitting period TDIM-ONTerminate, as shown in Figure 5.
With Fig. 3 in comparison, in light-emitting period TDIM-ONPredeterminated voltage V after beginning, in Fig. 5CSONAnd minimum feedback electricity
Pressure VFBMINIt has been respectively provided with the rate of climb and decrease speed faster.Therefore, with the LED controller of LED controller 60 replacement Fig. 1
The light modulation linearity of the LED driving circuit 10 of Fig. 1 when 14, can be improved, and mitigate light emitting diode string S1-S4 can
The scintillation that can occur.
Fig. 6 shows a kind of embodiment of transducer 64, and it has a switch 68 and a transducer 70.When switch 68 is to open
Lu Shi, the outfan of transducer 64 is high impedance.When switching 68 short circuit, transducer 70 is according to minimum back voltage VFBMINWith ginseng
Examine voltage VREFDifference, produced electric current just can reach the outfan of transducer 64.Fig. 6 simultaneously is not used to limit transducer 64
Enforcement.Circuit design industry simply can otherwise be designed other kind and turn according to the explanation of this specification and teaching
Lead device so as to have as transducer 64 or similar functional purpose.
The LED controller 80 that Fig. 7 citing is implemented according to the present invention.Different from coupling circuit 62 from Fig. 4, in Fig. 7
The pressure period T being defined from coupling circuit 82FORCEIt has been not necessarily set time length, its end time is by current detecting
Voltage V1CS-V4CSDetermined.
Include MAXIMUM SELECTION device 84, comparator 86 and gate 88 from coupling circuit 82.MAXIMUM SELECTION device 84 provides
Checking of great current voltage VCSMAX, corresponding current detection voltage V1CS-V4CSIn maximum.From from coupling circuit 82 it can be deduced that work as
Dim signal SDIMChange into 1 by 0, declare light-emitting period TDIM-ONDuring beginning, enable signal SENWill be because of current detection voltage V1CS-
V4CSAll also near 0V, so still stopping 0 logically.Until current detection voltage V1CS-V4CSWherein appoint
What sufficiently high, output transition for comparator 86, just can make enable signal SEN0 logically is changed into 1.Therefore, from coupling electricity
Road 82 is defined to force period TFORCE, it is initially by dim signal SDIMDetermine, and terminating is by current detection voltage
V1CS-V4CSIn maximum determine.
For example, in one embodiment, as current detection voltage V1CS-V4CSIn maximum be more than a preset reference
Voltage VCS-OKWhen, from coupling circuit 82, just period T is forced in declarationFORCETerminate；And reference voltage VCS-OKVery close to, but be less than and make LED
The predeterminated voltage V of string stabilized illuminationCSON.For example, predeterminated voltage VCSONThe reference voltage V for 0.4VCS-OKFor 0.3V.Reference
Voltage VCS-OKCorresponding driving current I1LED-I4LEDDefault driving current value ICS-OK.In other words, when driving current I1LED-
I4LEDExceed this default driving current value ICS-OK, during very close to its steady state operation value, from coupling circuit 82, just the period is forced in declaration
TFORCETerminate.
When Fig. 8 shows the LED controller 14 of LED controller 80 replacement Fig. 1, the signal waveform being likely to occur.By upper and
Under, it is sequentially dim signal SDIM, minimum back voltage VFBMIN, enable signal SEN, offset voltage VCOM, control voltage V1GAT, electricity
Stream detection voltage V1CS, and pulse-width signal SDRV.As shown in Figure 8, as current detection voltage V1CSExceed with reference to electricity
Pressure VCS-OKWhen, force period TFORCETerminate.Similar with Fig. 5, because there being pressure period TFORCEPresence, in Fig. 8 electric current inspection
Survey voltage V1CSAnd minimum back voltage VFBMINIt has been respectively provided with the rate of climb and decrease speed faster.Therefore, LED controls
During the LED controller 14 of device 80 replacement Fig. 1, it is possibility to have preferably dim the linearity, and mitigate light emitting diode string S1-S4 can
The scintillation that can occur.
Whether in the diagram force period T from coupling circuit 62 or Fig. 7 from coupling circuit 82 is definedFORCE, boosting
The feedback control of device 12 is all interrupted, so booster 12 is forced to transmit a fixing electrical power.If offset voltage VCOMCause
For some reason drifts and exceed steady state voltage value VCOM-ONOnce, define an oversize and fixing pressure from coupling circuit 62
Period TFORCE, that booster 12 is in pressure period TFORCEMiddle transmitted electrical power will have an opportunity to make driving power supply V very muchOUTOccur
Unnecessary too high voltages.In comparison, from coupling circuit 82 in driving current I1LED-I4LEDSet up similar when, that is,
In current detection voltage V1CS-V4CSMore than or equal to reference voltage VCS-OKWhen, just the feedback control recovery to booster 12, have
Chance avoids forcing period TFORCEThe too high voltages that may cause.
In embodiments of the invention, after this light-emitting period starts one forces the period, so that compensating electric capacity is held from coupling circuit
Observe offset voltage, force a booster to provide suitable electrical power and light to diode string.Therefore, in the enforcement of the present invention
Example can obtain the preferably light modulation linearity, or even eliminates possible scintillation.
The foregoing is only presently preferred embodiments of the present invention, the impartial change that all claim under this invention is done with repair
Decorations, all should belong to the covering scope of the present invention.
Claims (11)
1. a kind of control circuit to light emitting diode, may be used to control the light modulation of at least one LED strip, this adjusting control circuit bag
Contain：
One current driving circuit, can optionally make one to drive a current through this LED strip, this light modulation according to a dim signal
Signal definable one light-emitting period and a non-luminous period；
One pulse-width modulation circuit, can produce a pulse-width signal, its controllable power switch, with the electricity in this LED strip
Source sets up a driving voltage, and this pulse-width signal produces according to a thermal compensation signal；
One feedback circuit, according to a back voltage of this LED strip, can drive a compensating electric capacity, set up this thermal compensation signal thereon；
And
One from coupling circuit, produces an enable signal, it controls an enable end of this feedback circuit, makes this feedback circuit luminous at this
Period start after one pressure the period in do not drive this compensating electric capacity.
2. control circuit as claimed in claim 1, wherein, this pressure period is a set time length.
3. control circuit as claimed in claim 1, wherein, when this driving current is higher than a preset value, this pressure period ties
Bundle.
4. control circuit as claimed in claim 3, wherein, when this dim signal makes this LED strip light, this driving current is big
It is about a steady state operation value, and this preset value is less than this steady state operation value.
5. control circuit as claimed in claim 1, wherein, this control circuit may be used to control the light modulation of several LED strip, this control
Circuit processed includes：
This pulse-width modulation circuit, can produce this pulse-width signal, and it can control this power switch, to share in these LED strip
A power end set up this driving voltage；And
This feedback circuit, according to a minimum back voltage, to drive this compensating electric capacity, wherein, these LED strip provide multiple respectively
Back voltage, the minima in this minimum back voltage these back voltage corresponding.
6. control circuit as claimed in claim 5, wherein, this current driving circuit, can be according to a dim signal, selectivity
Several driving currents that make respectively respectively flow through these LED strip.
7. control circuit as claimed in claim 6, wherein, when these driving currents therein are higher than a preset value, should
The period is forced to terminate.
8. control circuit as claimed in claim 5, wherein, this pressure period is a set time length.
9. control circuit as claimed in claim 1, wherein, should include from coupling circuit：
One, from coupling switch, is coupled between this feedback circuit and this compensating electric capacity；And
One pulse generator, when this dim signal turns forbidden energy by enable, in order to produce a pulse, to define this pressure period.
10. control circuit as claimed in claim 1, wherein, should include from coupling circuit：
One comparator, in order to compare this driving current and a preset value, when this driving current is higher than this preset value, this comparator
Terminate this pressure period.
11. control circuits as claimed in claim 1, wherein, this feedback circuit includes a transducer, and, in this pressure
Period and this non-luminous period, the one of this transducer is output as high impedance.
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|---|---|---|---|
| CN201310420472.8A CN104470030B (en) | 2013-09-16 | 2013-09-16 | The control circuit of light emitting diode |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201310420472.8A CN104470030B (en) | 2013-09-16 | 2013-09-16 | The control circuit of light emitting diode |
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| CN104470030A CN104470030A (en) | 2015-03-25 |
| CN104470030B true CN104470030B (en) | 2017-03-01 |
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| CN201310420472.8A Active CN104470030B (en) | 2013-09-16 | 2013-09-16 | The control circuit of light emitting diode |
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Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| US20150366011A1 (en) * | 2014-06-13 | 2015-12-17 | O2Micro, Inc. | Light source controllers |
| CN105282907B (en) * | 2014-07-07 | 2017-08-25 | 盛群半导体股份有限公司 | LED backlight drive device |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| TW201117505A (en) * | 2009-11-11 | 2011-05-16 | Top Victory Invest Ltd | Driver for light-emitting diode (LED) light source |
| CN101588664B (en) * | 2008-05-21 | 2012-12-05 | 原景科技股份有限公司 | Light emitting diode drive circuit and circuit for controlling power switch |
| CN202617429U (en) * | 2012-05-14 | 2012-12-19 | 浩阳半导体股份有限公司 | Constant current driving device |
-
2013
- 2013-09-16 CN CN201310420472.8A patent/CN104470030B/en active Active
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101588664B (en) * | 2008-05-21 | 2012-12-05 | 原景科技股份有限公司 | Light emitting diode drive circuit and circuit for controlling power switch |
| TW201117505A (en) * | 2009-11-11 | 2011-05-16 | Top Victory Invest Ltd | Driver for light-emitting diode (LED) light source |
| CN202617429U (en) * | 2012-05-14 | 2012-12-19 | 浩阳半导体股份有限公司 | Constant current driving device |
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