CN105307310A - Low-dropout constant current LED driving method - Google Patents
Low-dropout constant current LED driving method Download PDFInfo
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- CN105307310A CN105307310A CN201410291266.6A CN201410291266A CN105307310A CN 105307310 A CN105307310 A CN 105307310A CN 201410291266 A CN201410291266 A CN 201410291266A CN 105307310 A CN105307310 A CN 105307310A
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Abstract
The invention relates to a low-dropout constant current LED driving method. A driving circuit comprises a single-chip microcomputer integrating AD sampling, a reference voltage source, Buck conversion circuits (C1, R1, Q1, D1, L1 and C2), operational amplifier input offset biasing circuits (R4 and R3), and LED current sampling and amplifying circuits (R2, U1, C3, R5, R6 and C4). The basic principle of the method is that the single-chip microcomputer outputs a PWM signal to control the outputs of the Buck circuits to reach the power of an LED, the current of the LED is detected by R2 and then is amplified by U1, the amplified current is fed back to the AD sampling input end of the single-chip microcomputer, and after being sampled, the current is compared by the program of the single-chip microcomputer to adjust output pulse width, thus forming a feedback loop to carry out constant current driving to the LED.
Description
Technical field
The present invention relates to field of liquid crystal display, in particular, relate to a kind of LED-backlit driving method.
Background technology
At present, in the LED illumination technology in powered battery situation, the technology of employing has: linear voltage decreasing constant current drives, use the constant current driving of the constant current driving of PWM voltage-dropping type chip, PWM booster type chip.The pluses and minuses that they exist are as following table:
Note: say in upper table whole efficiency refer to the overall power (comprise the consumption of single-chip microcomputer) of LED driving power than upper product.
As can be seen here, the present invention has very large advantage in every respect under low voltage condition, mean that we can use single-unit reason battery to power to LED and also can have good performance, and single-unit reason battery brings optimization can to other aspects of product, such as 1) the equilibrium treatment circuit of charging during multisection lithium battery series connection is simplified, do not need to carry out screening coupling to the lithium battery of series connection, between invisible, extend the life-span of lithium battery cycle charging yet.2) due to high efficiency, providing in identical lighting hours situation, the configuration of product in system can be reduced, save system cost.
Summary of the invention
For solving the problem, the invention provides a kind of method of low voltage difference constant-current driving LED, it adapts to low voltage difference situation, can constant-current driving LED and reference constant current is large, can have efficientibility and low cost.
Drive circuit sampled by integrated AD single-chip microcomputer, reference voltage source, Buck translation circuit (C1, R1, Q1, D1, L1, C2), amplifier input imbalance biasing circuit (R4, R3), LED current sampling and amplifying circuit (R2, U1, C3, R5, R6, C4) form.Its general principle is, the power outputting to LED of single-chip microcomputer output pwm signal control Buck circuit, R2 detects LED current, after U1 amplifies, feed back to Chip Microcomputer A/D sampling input, compared the pulsewidth of rear adjustment output after sampling by the program of single-chip microcomputer, so form a feedback circulation, constant current driving can be carried out to LED.
In Buck translation circuit, C1 is power filtering capacitor, and Q1 is pmos type switching tube, and R1 is Q1 grid pull-up resistor, and D1 is Schottky type diode, plays afterflow effect; L1 is energy storage inductor, and C2 is the filter capacitor that a capacity is larger.Buck structure is a disclosed current techique, no longer describes principle here.
It should be noted that, mode of operation and the commonsense method of Buck of the present invention are different.Buck generally can work in 3 kinds of patterns, continuous current mode, discontinuous current pattern and critical current pattern.Usual way is under allowing it be operated in continuous current mode, and the present invention is operated in discontinuous current mode.
The ripple of continuous current mode is less compared with other patterns, but the inductance value of the inductance L 1 needed is comparatively large, and (frequency of the pwm signal that usual single-chip microcomputer exports is not high, between tens KHz to tens KHz), so the volume of inductance or the DC internal resistance (DCR) of inductance also become greatly, are unfavorable for realizing efficient performance index.Present invention obviates traditional method, and under allowing Buck translation circuit operate mainly in discontinuous current pattern, make it possible to use small size inductance, the DCR of its inductance is very little, easily realizes efficient and low voltage difference characteristic.Under this mode, output ripple can be higher, and therefore we employ the larger filter capacitor C2 of a capacitance, to reduce ripple at output.
Current sample and amplifying circuit are made up of R2, U1, C3, R5, R6, C4, wherein R2 is sampling resistor, and the electric current of LED will produce voltage drop on R2, and U1, R5, R6, C4 form a direct current amplifier, be responsible for the voltage on R2 to amplify, deliver to single-chip microcomputer and carry out AD conversion.The multiplication factor of U1 is determined by R5, R6, and the effect of C4 reduces the higher ripple of frequency.
Because the resistance of R2 is very little, when using small current driving LED, very little (the such as R2=0.05 Europe of pressure drop of R2, LED current=20mA, so pressure drop=1mV of R2), for direct current amplifies, the input offset voltage of amplifier all may be greater than 1mV, therefore will cause cisco unity malfunction.Therefore the present invention has superposed a bias voltage (being made up of a reference source, R3, R4) at the positive input terminal of amplifier, and its biased amplitude, a little more than the input offset voltage of amplifier, allows it be in positive bias, ensures like this:
Positive bias voltage-input offset voltage >0
The maximum output voltage swing of (maximum pressure drop on positive bias voltage+R2) × multiplication factor < amplifier
So all the time, the output services of amplifier can be made in linear condition, owing to solving the problem of amplifier input imbalance, greatly extend the possibility at small area analysis current constant control.
The power supply of amplifier is by Single-chip Controlling, and to reduce the power consumption do not used, C3 is the decoupling capacitance of amplifier power end.
When not driving LED electric current, single-chip microcomputer is opened amplifier power supply and is learnt, record the output voltage after being biased, its value is deposited in the eeprom of single-chip microcomputer, when normally using, Single Chip Microcomputer (SCM) program deducts this truth of a matter, just obtains actual value, so complete correct sampling, eliminate amplifier input offset error.According to the actual conditions of product, can power on or in use learn.
The invention has the beneficial effects as follows: 1) adapt to low voltage difference situation, 2) can constant-current driving LED and reference constant current is large, 3) efficientibility and low cost can be had.
Accompanying drawing explanation
Fig. 1 is the circuit theory diagrams of low voltage difference constant-current driving LED of the present invention;
Fig. 2 is the learning process schematic diagram that powers on of single-chip microcomputer of the present invention.
Embodiment
Drive circuit sampled by integrated AD single-chip microcomputer, reference voltage source, Buck translation circuit (C1, R1, Q1, D1, L1, C2), amplifier input imbalance biasing circuit (R4, R3), LED current sampling and amplifying circuit (R2, U1, C3, R5, R6, C4) form.Its general principle is, the power outputting to LED of single-chip microcomputer output pwm signal control Buck circuit, R2 detects LED current, after U1 amplifies, feed back to Chip Microcomputer A/D sampling input, compared the pulsewidth of rear adjustment output after sampling by the program of single-chip microcomputer, so form a feedback circulation, constant current driving can be carried out to LED.
In Buck translation circuit, C1 is power filtering capacitor, and Q1 is pmos type switching tube, and R1 is Q1 grid pull-up resistor, and D1 is Schottky type diode, plays afterflow effect; L1 is energy storage inductor, and C2 is the filter capacitor that a capacity is larger.Buck structure is a disclosed current techique, no longer describes principle here.
It should be noted that, mode of operation and the commonsense method of Buck of the present invention are different.Buck generally can work in 3 kinds of patterns, continuous current mode, discontinuous current pattern and critical current pattern.Usual way is under allowing it be operated in continuous current mode, and the present invention is operated in discontinuous current mode.
The ripple of continuous current mode is less compared with other patterns, but the inductance value of the inductance L 1 needed is comparatively large, and (frequency of the pwm signal that usual single-chip microcomputer exports is not high, between tens KHz to tens KHz), so the volume of inductance or the DC internal resistance (DCR) of inductance also become greatly, are unfavorable for realizing efficient performance index.Present invention obviates traditional method, and under allowing Buck translation circuit operate mainly in discontinuous current pattern, make it possible to use small size inductance, the DCR of its inductance is very little, easily realizes efficient and low voltage difference characteristic.Under this mode, output ripple can be higher, and therefore we employ the larger filter capacitor C2 of a capacitance, to reduce ripple at output.
Current sample and amplifying circuit are made up of R2, U1, C3, R5, R6, C4, wherein R2 is sampling resistor, and the electric current of LED will produce voltage drop on R2, and U1, R5, R6, C4 form a direct current amplifier, be responsible for the voltage on R2 to amplify, deliver to single-chip microcomputer and carry out AD conversion.The multiplication factor of U1 is determined by R5, R6, and the effect of C4 reduces the higher ripple of frequency.
Because the resistance of R2 is very little, when using small current driving LED, very little (the such as R2=0.05 Europe of pressure drop of R2, LED current=20mA, so pressure drop=1mV of R2), for direct current amplifies, the input offset voltage of amplifier all may be greater than 1mV, therefore will cause cisco unity malfunction.Therefore the present invention has superposed a bias voltage (being made up of a reference source, R3, R4) at the positive input terminal of amplifier, and its biased amplitude, a little more than the input offset voltage of amplifier, allows it be in positive bias, ensures like this:
Positive bias voltage-input offset voltage >0
The maximum output voltage swing of (maximum pressure drop on positive bias voltage+R2) × multiplication factor < amplifier
So all the time, the output services of amplifier can be made in linear condition, owing to solving the problem of amplifier input imbalance, greatly extend the possibility at small area analysis current constant control.
The power supply of amplifier is by Single-chip Controlling, and to reduce the power consumption do not used, C3 is the decoupling capacitance of amplifier power end.
When not driving LED electric current, single-chip microcomputer is opened amplifier power supply and is learnt, record the output voltage after being biased, its value is deposited in the eeprom of single-chip microcomputer, when normally using, Single Chip Microcomputer (SCM) program deducts this truth of a matter, just obtains actual value, so complete correct sampling, eliminate amplifier input offset error.According to the actual conditions of product, can power on or in use learn.
Claims (5)
1. the method for a low voltage difference constant-current driving LED, it is characterized in that: drive circuit comprises the single-chip microcomputer that integrated AD samples, reference voltage source, Buck translation circuit (C1, R1, Q1, D1, L1, C2), amplifier input imbalance biasing circuit (R4, R3), LED current sampling and amplifying circuit (R2, U1, C3, R5, R6, C4), wherein, the power outputting to LED of single-chip microcomputer output pwm signal control Buck circuit, R2 detects LED current, after U1 amplifies, feed back to Chip Microcomputer A/D sampling input, compared the pulsewidth of rear adjustment output by the program of single-chip microcomputer after sampling, the circulation of formation like this one feedback, constant current driving can be carried out to LED.
2. the method for a kind of low voltage difference constant-current driving LED according to claim 1, is characterized in that: described Buck translation circuit is at discontinuous current MODE of operation, and use small size inductance, the DC internal resistance of its inductance is very little, realizes efficient and low voltage difference characteristic.
3. the method for a kind of low voltage difference constant-current driving LED according to claim 2, is characterized in that: the filter capacitor C2 in described Buck translation circuit adopts the filter capacitor of larger capacitance, to lower ripple.
4. the method for a kind of low voltage difference constant-current driving LED according to claim 1, it is characterized in that: the electric current of the LED sampling resistor R2 in described LED current sampling and amplifying circuit produces voltage drop, and voltage is delivered to single-chip microcomputer after being exaggerated on sampling resistor R2 and carried out AD conversion.
5. the method for a kind of low voltage difference constant-current driving LED according to claim 1, it is characterized in that: when not driving LED electric current, single-chip microcomputer is opened amplifier power supply and is learnt, record the output voltage after being biased, its value is deposited in the eeprom of single-chip microcomputer, when normally using, Single Chip Microcomputer (SCM) program deducts this truth of a matter, just obtain actual value, so complete correct sampling, eliminate amplifier input offset error.
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| Application Number | Priority Date | Filing Date | Title |
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| CN201410291266.6A CN105307310A (en) | 2014-06-25 | 2014-06-25 | Low-dropout constant current LED driving method |
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| CN201410291266.6A CN105307310A (en) | 2014-06-25 | 2014-06-25 | Low-dropout constant current LED driving method |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107635322A (en) * | 2017-10-27 | 2018-01-26 | 国网山东省电力公司商河县供电公司 | A kind of Dimmable LED constant-current drive circuit |
| CN109856445A (en) * | 2019-03-21 | 2019-06-07 | 黄河科技学院 | A kind of current sampling circuit that DC error can be eliminated for BUCK converter |
| CN112399676A (en) * | 2020-12-04 | 2021-02-23 | 欧普照明股份有限公司 | Constant current driving circuit, calibration method thereof and lighting device |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN203225910U (en) * | 2013-03-06 | 2013-10-02 | 陈小莉 | LED drive circuit |
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2014
- 2014-06-25 CN CN201410291266.6A patent/CN105307310A/en active Pending
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN203225910U (en) * | 2013-03-06 | 2013-10-02 | 陈小莉 | LED drive circuit |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107635322A (en) * | 2017-10-27 | 2018-01-26 | 国网山东省电力公司商河县供电公司 | A kind of Dimmable LED constant-current drive circuit |
| CN109856445A (en) * | 2019-03-21 | 2019-06-07 | 黄河科技学院 | A kind of current sampling circuit that DC error can be eliminated for BUCK converter |
| CN109856445B (en) * | 2019-03-21 | 2020-11-24 | 黄河科技学院 | Current sampling circuit for BUCK converter capable of eliminating direct current error |
| CN112399676A (en) * | 2020-12-04 | 2021-02-23 | 欧普照明股份有限公司 | Constant current driving circuit, calibration method thereof and lighting device |
| CN112399676B (en) * | 2020-12-04 | 2023-08-29 | 欧普照明股份有限公司 | Constant current driving circuit, calibration method thereof and lighting device |
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Application publication date: 20160203 |