CN101848575B - Driving circuit for backlight system of light-emitting diode - Google Patents
Driving circuit for backlight system of light-emitting diode Download PDFInfo
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- CN101848575B CN101848575B CN2009101193532A CN200910119353A CN101848575B CN 101848575 B CN101848575 B CN 101848575B CN 2009101193532 A CN2009101193532 A CN 2009101193532A CN 200910119353 A CN200910119353 A CN 200910119353A CN 101848575 B CN101848575 B CN 101848575B
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- operational amplifier
- electrically connected
- transistor
- driving circuit
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Abstract
The invention discloses a driving circuit for a backlight system of a light-emitting diode, which comprises input voltage, input resistance, an operational amplifier, a first transistor and a current arithmetic unit, wherein the positive input end of the operational amplifier is electrically connected with the input voltage through the input resistance, and the output end of the operational amplifier is electrically connected with the negative input end of the operational amplifier through a feedback network; the first transistor is used for acquiring reference current according to the input voltage and the input resistance to control the output voltage of the operational amplifier; and the current arithmetic unit is used for generating a plurality of operating currents which are proportional to the reference current according to the output voltage of the operational amplifier to drive a plurality of light-emitting diode series groups.
Description
Technical field
The present invention is meant a kind of driving circuit that is used for backlight system of light-emitting diode, refers to a kind of driving circuit with constant current source mode driven for emitting lights diode backlight system especially
Background technology
Because liquid crystal panel itself can be not luminous, so LCD must rely on backlight module light source sufficient and that be evenly distributed is provided, with display image normally.Traditionally, (Code CathodeFluorescent Lamp CCFL) because of having advantages such as high brightness and low cost, and becomes the main lighting source of LCD to cold-cathode tube.Yet; New line and light emitting diode (Light EmittingDiode along with environmental consciousness; LED) development of technology; The cold-cathode tube of mercurous composition is high by color saturation gradually, volume is little, power saving and the fast light emitting diode of reaction velocity replace, to satisfy the user to the demand of LCD on characteristics such as color, volume, life-span.
Generally speaking, the type of drive of light emitting diode is broadly divided into voltage source driving and two kinds of driven with current sources.Please refer to Fig. 1, Fig. 1 has explained the synoptic diagram that drives a backlight system of light-emitting diode 10 with the voltage source mode.As shown in Figure 1, backlight system of light-emitting diode 10 is to be composed in parallel by light emitting diode D1～Dn, and sees through the size of current that current-limiting resistance S1～Sn controls each light emitting diode of flowing through, to reach the purpose of the brightness of controlling each light emitting diode.Yet this kind type of drive is easily because of current-limiting resistance and the light emitting diode error between forward voltage forward, makes the flow through electric current of each light emitting diode different, and causes back light system to produce the uneven phenomenon of Luminance Distribution.
In order to improve the uneven phenomenon of Luminance Distribution; Back light system can change light emitting diode into arranged in series by the mode of being arranged in parallel, and is as shown in Figure 2, so not only can make the electric current of every light emitting diode identical; And owing to reduce the use of current-limiting resistance, and improve the power supply service efficiency of back light system.Yet; Because can raising with temperature, the forward forward voltage of light emitting diode descends; Therefore following in same drive voltage, the electric current of the light emitting diode series of flowing through will raise and rise with temperature, cause the brightness meeting of light emitting diode to change with temperature variation.
Therefore; The known backlit system generally can so that the size of current of each light emitting diode of flowing through is equal, and avoid its size of current to change with temperature variation with current source mode driven for emitting lights diode series; Thereby control the brightness of light emitting diode effectively, as shown in Figure 3.Under this situation, how in back light system, to provide an efficient constant current source driving circuit to become an important problem.
Summary of the invention
Therefore, the object of the invention promptly is to provide a kind of driving circuit that is used for backlight system of light-emitting diode.
The present invention discloses a kind of driving circuit that is used for backlight system of light-emitting diode.This driving circuit includes an input voltage, an input resistance, an operational amplifier, a first transistor and a current operator unit.This operational amplifier has a positive input terminal, a negative input end and an output terminal, and this positive input terminal sees through this input resistance and is electrically connected at this input voltage, and this output terminal is electrically connected at this negative input end through a beta-network.This first transistor has this positive input terminal that one first end is electrically connected at this operational amplifier; One second end sees through a reference resistance and is electrically connected at a reference voltage; And one the 3rd end be electrically connected at this output terminal of this operational amplifier; Be used for drawing a reference current, to control an output voltage of this operational amplifier according to this input voltage and this input resistance.This current operator unit is electrically connected at this output terminal and this reference voltage of this operational amplifier; Be used for this output voltage according to this operational amplifier; Produce and the proportional a plurality of working currents of this reference current, to drive a plurality of light emitting diode series.
Compared with prior art, driving circuit of the present invention can produce and the irrelevant steady operation electric current of load, with driven for emitting lights diode series according to input voltage and input resistance.Thus, the present invention not only can effectively reduce the difference between current between each light emitting diode series, also can avoid its size of current to change with temperature variation, thereby controls the brightness of light emitting diode effectively.In addition, the present invention can realize having the back light system of dimming function in addition by simple circuit, to reduce circuit complexity and cost.
Description of drawings
Fig. 1 has explained the synoptic diagram that drives a backlight system of light-emitting diode with the voltage source mode;
Fig. 2 has explained the synoptic diagram that drives another backlight system of light-emitting diode with the voltage source mode;
Fig. 3 has explained the synoptic diagram that drives a backlight system of light-emitting diode with the current source mode;
Fig. 4 is used for the synoptic diagram of the one drive circuit of backlight system of light-emitting diode for the embodiment of the invention;
Fig. 5 is used for the embodiment synoptic diagram of another driving circuit of backlight system of light-emitting diode for the present invention;
Fig. 6 is used for the embodiment synoptic diagram of another true driving circuit of backlight system of light-emitting diode for the present invention;
Fig. 7 is the coherent signal oscillogram of Fig. 6 driving circuit.
[primary clustering symbol description]
10 backlight system of light-emitting diode D1～Dn light emitting diode
S1～Sn, R2～Rn current-limiting resistance Vdc voltage source
Is current source 40,50,60 driving circuits
Vin input voltage Rin input resistance
OP1 operational amplifier Q1～Qn transistor
41,51,61 beta-networks, 42,52,62 current operator unit
Vgg reference voltage I1 reference current
Vout output voltage I2～In working current
LED_2～LED_n light emitting diode series Cf feedbacks electric capacity
65 controller of pulse width modulation
Embodiment
In the middle of instructions and claims, used some vocabulary to censure specific assembly.Having common knowledge the knowledgeable in the affiliated field should understand, and same assembly may be called with different nouns by manufacturer.This instructions and claims are not used as distinguishing the mode of assembly with the difference of title, but the benchmark that is used as distinguishing with the difference of assembly on function.Be to be an open term mentioned " comprising " in the middle of instructions and the follow-up claim in the whole text, so should be construed to " comprise but be not limited to ".In addition, " electric connection " speech is to comprise any indirect means that are electrically connected that directly reach at this.Therefore, be electrically connected at one second device, then represent this first device can be directly connected in this second device, or be connected to this second device through other device or the intersegmental ground connection of connection hand if describe one first device in the literary composition.
Please refer to Fig. 4, Fig. 4 is used for a light emitting diode (Light EmittingDiode, LED) synoptic diagram of the one drive circuit 40 of back light system for the embodiment of the invention.Driving circuit 40 includes an input voltage vin, an input resistance Rin, an operational amplifier OP1, a first transistor Q1 and a current operator unit 42.The positive input terminal of operational amplifier OP1 sees through input resistance Rin and is electrically connected at input voltage vin, and its output terminal is electrically connected at negative input end through a beta-network 41.The first transistor Q1 preferably is a two-carrier junction transistor (Bipolar Junction Transistor; BJT), its collection utmost point is electrically connected at the positive input terminal of operational amplifier OP1, and emitter-base bandgap grading sees through a reference resistance R1 and is electrically connected at a reference voltage Vgg; And base stage is electrically connected at the output terminal of operational amplifier OP1; Be used for drawing a reference current I1, with the output voltage V out of control operational amplifier OP1 according to input voltage vin and input resistance Rin.Current operator unit 42 is electrically connected at output terminal and the reference voltage Vgg of operational amplifier OP1; Be used for output voltage V out according to operational amplifier; Produce and the proportional working current I2～In of reference current I1, with driven for emitting lights diode series LED_2～LED_n.
Preferably, beta-network 41 is to be made up of a back coupling capacitor C f and a feedback resistance Rf.The end of back coupling capacitor C f is electrically connected at the output terminal of operational amplifier OP1, and the other end then is electrically connected at the negative input end of operational amplifier OP1; The end of feedback resistance Rf is electrically connected at negative input end and the back coupling capacitor C f of operational amplifier OP1, and the other end then is electrically connected at a ground end, and is as shown in Figure 4.In addition, current operator unit 42 also includes transistor seconds Q2～Qn, and it is all the two-carrier junction transistor, and has the electrical specification that is same as the first transistor Q1.The collection utmost point of transistor seconds Q2～Qn is electrically connected at light emitting diode series LED_2～LED_n respectively; Emitter-base bandgap grading sees through current-limiting resistance R2～Rn respectively and is electrically connected at reference voltage Vgg; Base stage then is electrically connected at the output terminal of operational amplifier OP1 respectively; Be used for size according to the output voltage V out and the corresponding current-limiting resistance of operational amplifier, produce and the proportional working current I2～In of reference current I1.About the detailed operation principle of driving circuit 40, please continue with reference to following explanation.
Because operational amplifier OP1 operates in the negative feedback configuration; Therefore positive input terminal and the negative input end of operational amplifier OP1 have the characteristic of imaginary short (virtual ground); And make the positive input terminal current potential of operational amplifier OP1 equal the current potential of negative input end, it can be expressed as:
V
(+)＝V
(-)＝0 (1)
Under this situation, the big young pathbreaker of the reference current I1 that the first transistor Q1 is drawn equals:
Because the collected current of the first transistor Q1 is similar to emitter current, so the output voltage V out of operational amplifier can be expressed as:
Vout＝Vbe+I1×R1+Vgg (3)
Wherein, Vbe represents the voltage difference of transistor base to emitter-base bandgap grading.In addition; Because transistor seconds Q2～Qn also need satisfy (3) formula, therefore when the equal and opposite in direction of current-limiting resistance R2～Rn during in reference resistance R1, i.e. R1=R2=Λ=Rn; Working current I2～In that transistor seconds Q2～Qn is produced also is equal to reference current I1, and it can be expressed from the next:
In other words; When the first transistor Q1 draws reference current I1 through input resistance Rin; Also determined simultaneously the output voltage V out size of operational amplifier, produced equal and opposite in direction in working current I2～In of reference current I1 with control transistor seconds Q2～Qn.
Therefore, driving circuit 40 of the present invention can produce and the irrelevant steady operation electric current I 2～In of load, with driven for emitting lights diode series LED_2～LED_n according to input voltage vin and input resistance Rin.Thus, the present invention not only can effectively reduce the difference between current between each light emitting diode series, also can avoid its size of current to change with temperature variation, thereby controls the brightness of light emitting diode effectively.
It should be noted that; Above-mentioned embodiment is merely of the present invention one explanation for example; This area tool knows that usually the knowledgeable revises when making according to the actual requirements suitably; For example adjust the size of current-limiting resistance R2～Rn, the working current I2～In that is produced with control transistor seconds Q2～Qn and proportionate relationship of reference current I1 or the like, it also belongs to scope of the present invention.
In addition, driving circuit of the present invention also can realize having the back light system of dimming function, controls with the brightness to light emitting diode.For instance, please refer to Fig. 5, Fig. 5 is used for the embodiment synoptic diagram of the one drive circuit 50 of backlight system of light-emitting diode for the present invention.Driving circuit 50 roughly is similar to the driving circuit 40 of the 4th figure, and difference is that driving circuit 50 also includes a voltage-regulating circuit 55, is coupled to input voltage vin, is used for adjusting the size of input voltage vin.Thus, driving circuit 50 of the present invention can be by the adjustment input voltage vin, and the working current size that control is produced is with the brightness of adjustment light emitting diode series LED_2～LED_n.
On the other hand, please continue with reference to figure 6, Fig. 6 is used for the embodiment synoptic diagram of the one drive circuit 60 of backlight system of light-emitting diode for the present invention.Compared to Fig. 5; Driving circuit 60 includes a pulse wave width modulation (Pulse Width Modulation; PWM) controller 65, are coupled to input voltage vin, are used for input voltage vin is carried out modulation; With the deration of signal by the adjustment input voltage vin, LED_2～LED_n carries out light modulation to the light emitting diode series.The coherent signal oscillogram is as shown in Figure 7, and its mode of operation is that this area tool knows that usually the knowledgeable knows, and does not add to give unnecessary details in this.
In sum, driving circuit of the present invention can produce and the irrelevant steady operation electric current of load, with driven for emitting lights diode series according to input voltage and input resistance.Thus, the present invention not only can effectively reduce the difference between current between each light emitting diode series, also can avoid its size of current to change with temperature variation, thereby controls the brightness of light emitting diode effectively.In addition, the present invention is also realized having the back light system of dimming function by simple circuit, to reduce circuit complexity and cost.
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 (9)
1. a driving circuit that is used for backlight system of light-emitting diode is characterized in that, includes:
One input voltage;
One input resistance;
One operational amplifier has a positive input terminal, a negative input end and an output terminal, and this positive input terminal sees through this input resistance and is electrically connected at this input voltage, and this output terminal sees through a beta-network and is electrically connected at this negative input end;
One the first transistor; Have one first end and be electrically connected at this positive input terminal of this operational amplifier; One second end sees through a reference resistance and is electrically connected at a reference voltage, and one the 3rd end is electrically connected at this output terminal of this operational amplifier, is used for according to this input voltage and this input resistance; Draw a reference current, to control an output voltage of this operational amplifier; And
One current operator unit; Be electrically connected at this output terminal and this reference voltage of this operational amplifier; Be used for this output voltage according to this operational amplifier, produce and the proportional a plurality of working currents of this reference current, to drive a plurality of light emitting diode series; This current operator unit pack contains a plurality of transistor secondses; Each transistor seconds of these a plurality of transistor secondses has the light emitting diode series that one first end is electrically connected at these a plurality of light emitting diode series; One second end sees through a current-limiting resistance and is electrically connected at this reference voltage; And one the 3rd end be electrically connected at this output terminal of this operational amplifier; Be used for this output voltage and this current-limiting resistance according to this operational amplifier, produce and the proportional working current of this reference current.
2. driving circuit as claimed in claim 1 is characterized in that, this beta-network includes:
One back coupling electric capacity have this output terminal that one first end is electrically connected at this operational amplifier, and one second end is electrically connected at this negative input end of this operational amplifier; And
One feedback resistance has one first end and be electrically connected at this negative input end of this operational amplifier and this second end of this back coupling electric capacity, and one second end is electrically connected at a ground end.
3. driving circuit as claimed in claim 1 is characterized in that, this first transistor is a two-carrier junction transistor, and this of this first transistor first end is a collection utmost point, and this second end is an emitter-base bandgap grading, and the 3rd end is a base stage.
4. driving circuit as claimed in claim 1; It is characterized in that each transistor seconds of these a plurality of transistor secondses is a two-carrier junction transistor, this of each transistor seconds first end is a collection utmost point; This second end is an emitter-base bandgap grading, and the 3rd end is a base stage.
5. driving circuit as claimed in claim 1 is characterized in that, when this current-limiting resistance and this reference resistance big or small identical, this working current that each transistor seconds produced of these a plurality of transistor secondses is equal to this reference current.
6. driving circuit as claimed in claim 1 is characterized in that the electrical specification of these a plurality of transistor secondses is same as this first transistor.
7. driving circuit as claimed in claim 1 is characterized in that, also comprises a voltage-regulating circuit, is coupled to this input voltage, is used for adjusting the size of this input voltage, so that these a plurality of light emitting diode series are carried out light modulation.
8. driving circuit as claimed in claim 1 is characterized in that, also comprises a controller of pulse width modulation, is coupled to this input voltage, is used for this input voltage is carried out modulation, so that these a plurality of light emitting diode series are carried out light modulation.
9. driving circuit as claimed in claim 1 is characterized in that, this driving circuit is to be used for a LCD.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN2009101193532A CN101848575B (en) | 2009-03-25 | 2009-03-25 | Driving circuit for backlight system of light-emitting diode |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN2009101193532A CN101848575B (en) | 2009-03-25 | 2009-03-25 | Driving circuit for backlight system of light-emitting diode |
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| Publication Number | Publication Date |
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| CN101848575A CN101848575A (en) | 2010-09-29 |
| CN101848575B true CN101848575B (en) | 2012-11-28 |
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| CN2009101193532A Expired - Fee Related CN101848575B (en) | 2009-03-25 | 2009-03-25 | Driving circuit for backlight system of light-emitting diode |
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Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN104252847B (en) * | 2013-06-25 | 2016-12-07 | 施耐德电器工业公司 | Light emitting module and control method thereof |
| TWI547210B (en) * | 2013-12-16 | 2016-08-21 | 立錡科技股份有限公司 | Light emitting device control circuit with dimming function and control method thereof |
| CN117475938A (en) * | 2020-11-13 | 2024-01-30 | 昂宝电子（上海）有限公司 | Multi-channel LED backlight system and constant current control circuit and method thereof |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101237728A (en) * | 2007-01-31 | 2008-08-06 | 中华映管股份有限公司 | LED backlight system and driving method of backlight source |
| CN101252800A (en) * | 2007-08-30 | 2008-08-27 | 崇贸科技股份有限公司 | LED drive circuit |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6734639B2 (en) * | 2001-08-15 | 2004-05-11 | Koninklijke Philips Electronics N.V. | Sample and hold method to achieve square-wave PWM current source for light emitting diode arrays |
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Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101237728A (en) * | 2007-01-31 | 2008-08-06 | 中华映管股份有限公司 | LED backlight system and driving method of backlight source |
| CN101252800A (en) * | 2007-08-30 | 2008-08-27 | 崇贸科技股份有限公司 | LED drive circuit |
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Granted publication date: 20121128 |