CN1802057A - Current source circuit for driving parallel LED - Google Patents
Current source circuit for driving parallel LED Download PDFInfo
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- CN1802057A CN1802057A CN200610023333.1A CN200610023333A CN1802057A CN 1802057 A CN1802057 A CN 1802057A CN 200610023333 A CN200610023333 A CN 200610023333A CN 1802057 A CN1802057 A CN 1802057A
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- current source
- operational amplifier
- transistor
- source circuit
- parallel connection
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Abstract
A current source circuit for driving parallel connection LED includes NMOS ( m 1, m 2 ) constituting electric current specula, a reference current source ( i < sub > b < / sub > ) connected with NMOS ( m 1 ), an operational amplifier operational amplifier ( A1 ), It features leak terminal voltage of MOS ( m 1 ) sampled to positive input end of operational amplifier operational amplifier ( A1 ), leak terminal voltage of MOS ( m 2 ) sampled to operational amplifier ( A1 ) negative input end, outputting of operational amplifier ( A1 ) connected to gate end of NMOS ( m 1 ) and NMOS ( m 2 ). Said invention can ensure driver stage work efficiency and good electric current matched precision between each channel LED.
Description
Technical field
The present invention relates to a kind of current source circuit that is used to drive parallel connection LED (light-emitting diode).
Background technology
White light LEDs is widely used in handheld device (mobile phone, MP3, MP4 etc.) at present.
Led drive circuit generally can be divided into two kinds, and a kind of is tandem drive, adopts inductive type DC-DC boost conversion principle, and all LED are connected in series; Another kind is in parallel the driving, adopts capacitive based charge pump multiplication of voltage principle, and all LED are connected in parallel.
The mode of tandem drive can guarantee that the electric current that all LED flow through is in full accord, and each channel LED can guarantee the brightness matching degree like this.For a bigger display screen, it can need a plurality of white light LEDs to come as backlight, and the mode of tandem drive can provide goodish LED currents match precision, thereby reaches uniform display brightness.
But a very big problem of tandem drive is exactly EMI (electromagnetic interference) problem, because the switching tube of tandem type drive circuit is operated in the high frequency on off operating mode, the fast transient process of high frequency is an interference source, external inductance can make that the radiation phenomenon of disturbing is quite serious, especially at mobile communication terminal, can bring very big influence to the receiving sensitivity of mobile communication terminal.
And parallel driver circuit, owing to be to adopt the charge pump of the electric capacity principle of boosting, its EMI of externally forming disturbs and just is far smaller than the tandem drive circuit so.But in parallel driver circuit, the matching degree that how to guarantee each parallel connection LED electric current is the problem that merits attention.
In the current source circuit of existing driving LED, generally obtain the required big electric current of LED (mA level) by little electric current of mirror image (uA level).
As depicted in figs. 1 and 2, I
BBe the current reference that other circuit provided, V1 can be same or different voltage sources with V2.V
DROPBe current source output required voltage.
As shown in Figure 1, under the equal situation of the drain terminal voltage of NMOS pipe M2 that constitutes current mirror and M1, M2 with the ratio of M1 electric current is:
I
M2/I
M1＝(W2/L2)/(W1/L1) (1)
W2, L2 are channel length and the channel width of M2, and W1 and L1 are channel length and the channel width of M1.
Its design defect is: because LED forward conduction voltage drop difference, thereby the source-drain voltage V of metal-oxide-semiconductor M2
DS2And be not equal to the source-drain voltage V of M1
DS1, the electric current variation meeting of the M2 that is caused by " raceway groove mudulation effect " greatly like this.And at V
DS2Under the very little situation, the M2 pipe enters linear zone, and output current can descend a lot.Be difficult to reach the requirement of the currents match precision between the LED like this.In parallel connection LED drive circuit, usually, require currents match precision between LED between 0.5% to 3%.
As shown in Figure 2, do not have in operational amplifier A 1 under the situation of offset voltage, metal-oxide-semiconductor M1 electric current with the ratio of reference current is:
I
M1/I
B＝R1/R2 (2)
The defective of this current source circuit is:
1, R2 meeting supported differential pressure, so a part of power consumption consumption has reduced efficient on the resistance.And under big output current situation, power consumed can significantly increase on the resistance R 2.Efficient Eff for output stage may be calculated:
Eff＝(V2-V
DROP)/V2 (3)
Obviously, V
DROPIncrease, efficient can reduce.
2, resistance R 1 and R2 need high matching degree, can have any problem in the chip internal realization.
3, above-mentioned 1 and 2 two constituted contradiction, more increased the difficulty that circuit is realized.Because realize the resistance of high matching degree, under common process condition, resistance value can not be too little.
4, because operational amplifier A 1 offset voltage V
OSDirectly be added on the small resistor R2, reduced the precision of output current.See formula 4.
I
R2＝(R1/R2)×I
R+V
OS/R2 (4)
Summary of the invention
The object of the present invention is to provide a kind of current source circuit that is used to drive parallel connection LED, it both can guarantee the operating efficiency of driving stage, guaranteed to have good currents match precision between each channel LED again simultaneously.
A kind of current source circuit that is used to drive parallel connection LED provided by the present invention comprises transistor M1, the M2 and a reference current source I who links to each other with transistor M1 that constitute current mirror
BAn and operational amplifier A 1, it is characterized in that: the drain terminal voltage of described transistor M1 is sampled to the positive input terminal of operational amplifier A 1, the drain terminal voltage of described transistor M2 is sampled to the negative input end of operational amplifier A 1, and the output of operational amplifier A 1 is connected to the transistor M1 of formation current mirror and the grid end of transistor M2.
Drive the current source circuit of parallel connection LED in above-mentioned being used for, the transistor that constitutes current mirror is the NMOS pipe.
Drive the current source circuit of parallel connection LED in above-mentioned being used for, the transistor that constitutes current mirror is the PMOS pipe.
Drive the current source circuit of parallel connection LED in above-mentioned being used for, the transistor that constitutes current mirror is the NPN pipe.
Drive the current source circuit of parallel connection LED in above-mentioned being used for, the transistor that constitutes current mirror is the PNP pipe.
Drive the current source circuit of parallel connection LED in above-mentioned being used for, the dc open-loop gain of operational amplifier A 1 is arranged on more than the 40dB.
Drive the current source circuit of parallel connection LED in above-mentioned being used for, transistor M1 and transistor M2 corresponding end voltage equate.
Owing to adopted above-mentioned technical solution, the present invention improves the current mirror that existing (shown in Figure 1) is used for driving the current source circuit of parallel connection LED, introduce the control loop that operational amplifier constitutes, by feasible two the transistor M1 that constitute current mirror of the control of amplifier amplifier, M2, as: the NMOS pipe, its source is leaked pressure reduction and is equated, thereby eliminated the raceway groove mudulation effect, even if under different LED situations, current mirror can guarantee designed proportionate relationship, and under very low source-drain voltage situation, M1 and M2 enter into linear zone, still can obtain proportionate relationship preferably.Such design has guaranteed that the current mirror ratio changes with the LED characteristic hardly, allows lower current source output voltage V simultaneously again
DROPThereby, make circuit that the high conversion rate of ratio be arranged.Therefore the present invention is used to drive parallel connection LED, both can guarantee the operating efficiency of driving stage, guarantees to have good currents match precision between each channel LED again simultaneously.
Description of drawings
Fig. 1 is existing a kind of schematic diagram that is used to drive the current source circuit of parallel connection LED;
Fig. 2 is the schematic diagram that existing another kind is used to drive the current source circuit of parallel connection LED;
Fig. 3 is the schematic diagram of the embodiment of the present invention's current source circuit of being used to drive parallel connection LED;
Fig. 4 is the schematic diagram of current source circuit practical application of the present invention.
Embodiment
As shown in Figure 3, the present invention is used to drive the current source circuit of parallel connection LED, comprises NMOS pipe M1, the M2 and a reference current source I who links to each other with NMOS pipe M1 that constitute current mirror
B, and an operational amplifier A 1.
The drain terminal voltage of NMOS pipe M1 is sampled to the positive input terminal of operational amplifier A 1, the drain terminal voltage of output current NMOS pipe M2 is sampled to the negative input end of operational amplifier A 1, and the output of operational amplifier A 1 is connected to the grid end that the NMOS that constitutes current mirror manages M1 and M2.Because the dc open-loop gain of operational amplifier A 1 more than 40dB, equates so can guarantee the positive-negative input end voltage of A1.The grid end of NMOS pipe M1, drain terminal, source end, underlayer voltage equate with the corresponding end voltage of NMOS pipe M2, so current ratio each other equals the ratio of its breadth length ratio:
I
M2/I
M1＝(W2/L2)/(W1/L1) (5)
W2, L2 are channel length and the channel width of M2, and W1 and L1 are channel length and the channel width of M1.Therefore the current mirror proportionate relationship is not subjected to the influence of LED characteristic or other device property, even under the very low situation of the M2 pipe source-drain voltage VDS2 that causes owing to the LED conduction voltage drop is bigger, output current still can guarantee high consistency.
Current source circuit of the present invention is made chip, is used to drive the multichannel white light LEDs, and each channel LED electric current of application requirements guarantees high matching degree.And in the practical application, the conduction voltage drop difference of different LED under the same current situation is bigger, may reach 200mV, even more.
Fig. 4 is actual circuit diagram.Wherein: V1 is an input voltage; V2 is the voltage of the chip internal circuit conversion driving LED of coming out, and it is according to the conduction voltage drop of LED and the needed operating voltage V of current source
DROPDetermined.I
B1And I
B2Be the reference current source that other module produced, its electric current equates.
The anode of all LED all is connected to same current potential V2, because the conduction voltage drop of D1, two LED of D2 and unequal has caused the drain terminal voltage of metal-oxide-semiconductor M1 and M2 unequal.The difference of LED characteristic can be compensated in this circuit like this.
The conduction voltage drop of D1 illustrates: if can cause V greater than the conduction voltage drop of D2
DROP2＜V
DROP1 'Because the control action of operational amplifier, the grid potential of metal-oxide-semiconductor M2 can be slightly higher than the grid electricity of M4, thus the electric current of M2 still can guarantee be:
I
M2/I
B1＝(W2/L2)/(W1/L1) (6)
The electric current of M4 is:
I
M4/I
B2＝(W4/L4)/(W3/L3) (7)
Because I
B2=I
B1, therefore as long as the breadth length ratio example is equal
I
M2＝I
M4 (8)
W and L are respectively the channel width and the channel length of corresponding metal-oxide-semiconductor.
Compare scheme illustrated in figures 1 and 2, under same application conditions (V1=3.6V drives white light LEDs, and electric current is output as 20mA, the output of two channel LEDs).If since the difference of LED pressure drop, V
DROP1=200mV, V
DROP1=400mV.The currents match degree of D1 and two LED of D2 is in ± 0.5% in this structure.The current precision of current source shown in Figure 1 is in ± 30%.The current precision of current source shown in Figure 2 is in ± 4%.
Based on above-mentioned same application conditions, if the LED conduction voltage drop is equal, for this current source circuit, loss pressure drop V on the current source
DROPOnly need 200mV, and method shown in Figure 2 needs 400mV.
Obviously current source circuit of the present invention has guaranteed high current precision and high conversion efficiency simultaneously.
Advantage of the present invention:
1, because the variation of LED characteristic causes the source and drain voltage VDS2 that exports NMOS pipe M2 to change, in the circuit that the present invention constructed, can carry out loop control by introducing operational amplifier, adjust the grid voltage of the NMOS pipe M1, the M2 that constitute current mirror, come the variation of compensation LED characteristic.The grid voltage of electric current source capsule can be lifted under the lower situation of the VDS2 voltage that is caused owing to the LED characteristic, and vice versa, played the effect of compensation LED characteristic variations like this.So can guarantee under various LED situations, output NMOS pipe M2 can be with constant current driven LED.
Even if 2 NMOS pipe M2 and M1 enter linear zone, as long as the reference current I that provides
B, the current ratio of M2 and M1 still can keep by the given proportionate relationship of formula 4, can reduce the dimensional requirement of big electric current output to M2 like this, promptly allows to use the M2 of relative reduced size to drive big electric current.
3, comprehensive above-mentioned 1,2 two points are not because this current mirror proportionate relationship relies on other device (as resistance etc.), so the voltage that loses on the current source is V
DROPVoltage ratio scheme illustrated in figures 1 and 2 is desired little.
Therefore, current source structure of the present invention has not only guaranteed the precision of output current, can also guarantee high conversion efficiency.
Above embodiment is only for the usefulness that the present invention is described, but not limitation of the present invention, person skilled in the relevant technique, under the situation that does not break away from the spirit and scope of the present invention, can also make various conversion or modification, therefore all technical schemes that are equal to also should belong within the category of the present invention, should be limited by each claim.And include within the scope of claim.
Claims (7)
1. a current source circuit that is used to drive parallel connection LED comprises two transistors (M1, M2) and a reference current source (I who links to each other with transistor (M1) that constitute current mirror
B), an and operational amplifier (A1), it is characterized in that: the drain terminal voltage of described transistor (M1) is sampled to the positive input terminal of operational amplifier (A1), the drain terminal voltage of described transistor (M2) is sampled to the negative input end of operational amplifier A 1, and the output of operational amplifier (A1) is connected to the transistor (M1) of formation current mirror and the grid end of transistor (M2).
2. the current source circuit that is used to drive parallel connection LED according to claim 1 is characterized in that: the transistor of described formation current mirror is the NMOS pipe.
3. the current source circuit that is used to drive parallel connection LED according to claim 1 is characterized in that: the transistor of described formation current mirror is the PMOS pipe.
4. the current source circuit that is used to drive parallel connection LED according to claim 1 is characterized in that: the transistor of described formation current mirror is the NPN pipe.
5. the current source circuit that is used to drive parallel connection LED according to claim 1 is characterized in that: the transistor of described formation current mirror is the PNP pipe.
6. the current source circuit that is used to drive parallel connection LED according to claim 1 is characterized in that: the dc open-loop gain of described operational amplifier (A1) is arranged on more than the 40dB.
7. the current source circuit that is used to drive parallel connection LED according to claim 1 is characterized in that: described transistor (M1) and transistor (M2) corresponding end voltage equate.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN200610023333.1A CN1802057A (en) | 2006-01-16 | 2006-01-16 | Current source circuit for driving parallel LED |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN200610023333.1A CN1802057A (en) | 2006-01-16 | 2006-01-16 | Current source circuit for driving parallel LED |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN1802057A true CN1802057A (en) | 2006-07-12 |
Family
ID=36811734
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN200610023333.1A Pending CN1802057A (en) | 2006-01-16 | 2006-01-16 | Current source circuit for driving parallel LED |
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Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102014544A (en) * | 2010-07-13 | 2011-04-13 | 深圳市航嘉驰源电气股份有限公司 | LED (Light-Emitting Diode) lamp driving circuit |
| CN102098852A (en) * | 2011-02-01 | 2011-06-15 | 北京大学 | Small-area power tube-based low-mismatching multi-channel light-emitting diode (LED) constant current source driving circuit |
| CN102612217A (en) * | 2012-02-27 | 2012-07-25 | 开源集成电路(苏州)有限公司 | LED driver circuit and chip |
| CN102625547A (en) * | 2012-04-23 | 2012-08-01 | 英飞特电子（杭州）有限公司 | Dimming signal interface circuit |
| CN101652004B (en) * | 2009-04-10 | 2013-01-23 | 成都芯源***有限公司 | White light LED circuit and method for controlling average current of white light LED |
| CN102067059B (en) * | 2008-04-28 | 2014-11-26 | 爱特梅尔公司 | Methods and circuits for triode region detection |
-
2006
- 2006-01-16 CN CN200610023333.1A patent/CN1802057A/en active Pending
Cited By (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102067059B (en) * | 2008-04-28 | 2014-11-26 | 爱特梅尔公司 | Methods and circuits for triode region detection |
| CN101652004B (en) * | 2009-04-10 | 2013-01-23 | 成都芯源***有限公司 | White light LED circuit and method for controlling average current of white light LED |
| CN102014544A (en) * | 2010-07-13 | 2011-04-13 | 深圳市航嘉驰源电气股份有限公司 | LED (Light-Emitting Diode) lamp driving circuit |
| CN102098852A (en) * | 2011-02-01 | 2011-06-15 | 北京大学 | Small-area power tube-based low-mismatching multi-channel light-emitting diode (LED) constant current source driving circuit |
| CN102098852B (en) * | 2011-02-01 | 2013-07-10 | 北京大学 | Small-area power tube-based low-mismatching multi-channel light-emitting diode (LED) constant current source driving circuit |
| CN102612217A (en) * | 2012-02-27 | 2012-07-25 | 开源集成电路(苏州)有限公司 | LED driver circuit and chip |
| CN102612217B (en) * | 2012-02-27 | 2014-08-06 | 开源集成电路(苏州)有限公司 | LED driver circuit and chip |
| CN102625547A (en) * | 2012-04-23 | 2012-08-01 | 英飞特电子（杭州）有限公司 | Dimming signal interface circuit |
| CN102625547B (en) * | 2012-04-23 | 2014-12-10 | 英飞特电子（杭州）股份有限公司 | Dimming signal interface circuit |
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