CN102685984A - LED (Light Emitting Diode) constant-current driving circuit - Google Patents
LED (Light Emitting Diode) constant-current driving circuit Download PDFInfo
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Abstract
The invention discloses an LED (Light Emitting Diode) constant-current driving circuit. The LED constant-current driving circuit comprises a voltage reference unit which is used for generating the reference voltage, a peak current detection keeping unit, an error amplifier unit, a current comparator unit, a demagnetization detection unit and a self-adaptive unit. According to the LED constant-current driving circuit disclosed by the invention, the LED constant-current control can be realized, the service life of an LED can be prolonged, the problem of CTR (Current Transmission Rate) attenuation of an optical coupler is overcome as the circuit is free from an optical coupler device, the stability of the circuit is increased, the EMI (Electro Magnetic Interference) and the harmonic distortion can be greatly improved as the switching frequency of a power switching tube of the circuit is a variable frequency, an external circuit can be greatly simplified by adopting the circuit, and the using cost can be greatly reduced.
Description
Technical field
The present invention relates to integrated circuit fields, particularly a kind of constant-current circuit that is applicable to that light-emitting diode (LED) drives.
Background technology
At present, the use of light-emitting diode (LED) is more and more universal, and the user has proposed increasingly high requirement to it.Wherein therefore electrical isolation and constant current control technology more and more come into one's own because of relating to safety and LED useful life.
The method of traditional realization electrical isolation and constant current control is to be realized by conventional magnetic energy induction feedback or optocoupler feedback system.Conventional magnetic energy induction feedback system is made up of auxilliary group winding and sampling filter circuit usually.Voltage on the auxilliary group winding can raise with the rising of output voltage, through this voltage of sampling, behind filter circuit, becomes direct voltage again, and the input and the voltage reference that after dividing potential drop, are connected to error amplifier compare.This kind circuit structure is simple, but unavoidably receives the influence of the factors such as spurious impedance of leakage inductance, winding spurious impedance and secondary current rectifying and wave filtering circuit, causes that voltage changes with secondary current on the auxilliary group winding, and then causes that output voltage changes; Auxilliary simultaneously group winding increases volume of transformer, and cost raises.The optocoupler feedback system is got output end voltage, compares with voltage reference through dividing potential drop again, makes the voltage reference cathode potential change, thereby changes the electric current of the optocoupler of flowing through, the final error voltage of realizing the change error amplifier.This kind circuit voltage regulation result is good, but the current transfer ratio of optocoupler (CTR) can decay with high temperature in time, make circuit unstable, and peripheral component is more, use inconvenience, and cost is higher.
Summary of the invention
To the deficiency of above-mentioned prior art, the purpose of this invention is to provide a kind of simple in structure and can realize the LED constant-current drive circuit of constant-current driving.
For solving the problems of the technologies described above, the present invention adopts following technical scheme:
A kind of LED constant-current drive circuit; Comprise transformer, switching signal generation unit, driver element; Said transformer comprises former limit winding, secondary winding and auxiliary winding, and said former limit winding is connected with the sampling resistor of a ground connection through a power switch pipe, and said switching signal generation unit is controlled the break-make of said power switch pipe through said driver element; Said secondary winding is connected with LED through current rectifying and wave filtering circuit; Said auxiliary winding and said secondary winding homophase, this circuit also comprises: the voltage reference unit is used to produce reference voltage; The peak current detection holding unit is used for when the power switch pipe conducting, the voltage on the sampling resistor being sampled, and when power switch pipe turn-offs, exports the crest voltage of sampling gained; Error amplifier unit, two inputs of said error amplifier unit are connected with the output of said voltage reference unit, the output of peak current detection holding unit respectively; The current comparator unit; Its negative input end connects the output of said error amplifier; Positive input terminal connects sampling resistor; Output connects the input of said switching signal generation unit, and when the positive input terminal voltage of current comparator unit during greater than negative input end voltage, the output of current comparator unit produces signal and makes said switching signal generation unit drive said power switch pipe to turn-off; The degaussing detecting unit is used to detect degaussing time of secondary winding; Adaptive unit is used for the automatic following calculation secondary winding degaussing time, and in the ratio of the setting certain hour of postponing automatically; And then drive said switching signal generation unit and make the power switch pipe conducting, said adaptive unit is connected with said degaussing detecting unit, switching signal generation unit, current comparator unit output.
Preferably, said auxiliary winding one end is connected with first divider resistance, and the other end of said first divider resistance is connected with second divider resistance and degaussing detecting unit respectively, and the other end ground connection of said second divider resistance also is connected with the other end of auxiliary winding.
Preferably; Said adaptive unit comprises first current source, second current source, first switch, second switch, the 3rd switch, electric capacity, rest-set flip-flop, hysteresis comparator and monostable flipflop; Said first current source is connected with the 3rd switch through first switch; Said second current source is connected with the 3rd switch through second switch; The other end of said the 3rd switch is connected with the positive input terminal of electric capacity and hysteresis comparator, said capacity earth, and the negative input end of said hysteresis comparator is connected with a reference voltage source; The output of said hysteresis comparator is connected with the input of said monostable flipflop; The output of said monostable flipflop is connected with said switching signal generation unit, and two inputs of said rest-set flip-flop are connected with the output and the degaussing detecting unit output of current comparator unit respectively, and two inputs of said rest-set flip-flop are connected with first switch, second switch respectively; Said the 3rd switch turn-offs when said power switch pipe conducting, conducting when said power switch pipe turn-offs.
Preferably, said rest-set flip-flop comprises first NOR gate, second NOR gate, and an input of said first NOR gate connects the output of said current comparator, and another input of said first NOR gate connects the output of second NOR gate; One input of said second NOR gate connects the output of degaussing detecting unit; Another input of said second NOR gate connects the output of first NOR gate; The output of said first NOR gate is controlled said first switch, and the output of said second NOR gate is controlled said second switch.
Technique scheme has following beneficial effect: 1) adopt this circuit can realize LED constant current control, the useful life of improving LED; 2) this circuit does not use optocoupler, thereby has overcome the problem of optocoupler CTR decay, has improved the stability of circuit; 3) adopt this circuit, the switching frequency of power switch pipe is frequency conversion, can greatly improve the distortion of EMI harmonic.4) adopt this circuit to simplify peripheral circuit greatly, application cost is reduced greatly.
Above-mentioned explanation only is the general introduction of technical scheme of the present invention, understands technological means of the present invention in order can more to know, and can implement according to the content of specification, below with preferred embodiment of the present invention and conjunction with figs. this patent is elaborated.
Description of drawings
Fig. 1 is the theory diagram of the embodiment of the invention.
Fig. 2 is fixing adaptive unit principle schematic.
Fig. 3 is the working waveform figure of the embodiment of the invention.
Embodiment
Below in conjunction with accompanying drawing the preferred embodiments of the present invention are described in detail.
As shown in Figure 1; This LED constant-current drive circuit comprises: transformer, voltage reference unit 1, peak current detection holding unit 2, error amplifier unit 3, current comparator unit 4, switching signal generation unit 5, driver element 6, adaptive unit 7 and degaussing detecting unit 8, voltage reference unit 1 is used to produce reference voltage V REF.
Transformer comprises former limit winding Np, secondary winding Ns and auxiliary winding NA, auxiliary winding NA and secondary winding Ns homophase.Former limit winding Np is connected with the sampling resistor Rcs of a ground connection through a power switch pipe P, and switching signal generation unit 5 is through the break-make of driver element 6 power controlling switching tube P.Former limit winding Np is connected with power supply Vin; Secondary winding Ns is connected with LED through current rectifying and wave filtering circuit; Current rectifying and wave filtering circuit comprises a diode and a capacitor C 0, and the break-make through power controlling switching tube P can make the NE BY ENERGY TRANSFER of former limit winding Np give secondary winding Ns, and then driving LED work.
Peak current detection holding unit 2 is used for when power switch pipe P conducting, the voltage on the sampling resistor Rcs being sampled, and when power switch pipe P turn-offs, exports the crest voltage of sampling gained.When power switch pipe P conducting; Peak current detection holding unit 2 is output as low level; When power switch pipe P turn-offed, the voltage Vsh of peak current detection holding unit 2 outputs was the crest voltage on the sampling resistor Rcs, promptly passed through the maximum voltage value of sampling resistor Rcs in the sampling time.
Two inputs of error amplifier unit 3 are connected with the output of voltage reference unit 1, the output of peak current detection holding unit 2 respectively; The output of error amplifier unit 3 is connected with the capacitor C 1 of ground connection and the negative input end of current comparator unit 4 respectively; Error amplifier Unit 3 keep the error amount of the output of peak current sample holding unit 2 and reference voltage V REF to amplify and as a reference data of current comparator 4,1 rectified action of capacitor C.Current comparator unit 4 positive input terminals are connected with adopting resistance R cs, and the output of current comparator unit 4 is connected with switching signal generation unit 5.As shown in Figure 3; When power switch pipe P conducting; Flow through and adopt the electric current I p of resistance R cs to increase gradually, adopt the voltage on the resistance R cs also to increase gradually, the voltage on adopting resistance R cs is during greater than the voltage of error amplifier 3 outputs; Current comparator unit 4 produces energizing signal and gives switching signal generation unit 5, and switching signal generation unit 5 is turn-offed through driver element 6 power controlling switching tube P.
Degaussing detecting unit 8 is used to detect the degaussing time of secondary winding.Since secondary winding Ns and auxiliary winding NA homophase, so the degaussing time of secondary winding Ns is identical with the degaussing time of auxiliary winding NA, and degaussing unit 8 just can be confirmed the degaussing time of secondary winding Ns through the degaussing time of detecting auxiliary winding NA.Auxiliary winding NA one end is connected with the first divider resistance R1, and the other end of the first divider resistance R1 is connected with the second divider resistance R2 and degaussing detecting unit 8 respectively, and the other end ground connection of the second divider resistance R2 also is connected with the other end of auxiliary winding NA.When secondary winding Ns degaussing; Its electric current I p descends gradually; When the electric current on the secondary winding Ns drops to zero; Voltage on the second divider resistance R2 also is converted into low level (be degaussing accomplish) from high level, and degaussing detecting unit 8 can be confirmed the degaussing time of secondary winding Ns through detecting voltage on the second divider resistance R2 like this.
Adaptive unit 7 is connected with the output of degaussing detecting unit 8, switching signal generation unit 5 and current comparator unit 4 respectively; Adaptive unit 7 is used for the automatic following calculation secondary winding Ns degaussing time; And in the ratio of the setting certain hour of postponing automatically, and then drive said switching signal generation unit 5 and make power switch pipe P conducting.
Adaptive unit 7 as shown in Figure 2,, comprise the first current source I1, the second current source I2, first switch SW 1, second switch SW2, the 3rd switch SW 3, capacitor C 2, rest-set flip-flop, hysteresis comparator 9 and monostable flipflop 10.The first current source I1 is connected with the 3rd switch SW 3 through first switch SW 1, and the second current source I2 is connected with the 3rd switch SW 3 through second switch SW2, and the other end of the 3rd switch SW 3 is connected with the positive input terminal of capacitor C 2 and hysteresis comparator 9, capacitor C 2 ground connection.The negative input end of hysteresis comparator 9 is connected with a reference voltage source VREF2, and the output of hysteresis comparator 9 is connected with the input of monostable flipflop 10, and the output of monostable flipflop 10 is connected 5 with the switching signal generation unit.
Rest-set flip-flop comprises the first NOR gate NOR1, the second NOR gate NOR2, and the input of the first NOR gate NOR1 connects the output CSOFF of current comparator, and another input of the first NOR gate NOR1 connects the output of the second NOR gate NOR2; The input of the second NOR gate NOR2 connects the output ZCD of degaussing detecting unit 8, and another input of the second NOR gate NOR2 connects the output of the first NOR gate NOR1.The output of the first NOR gate NOR1 is connected with first switch SW 1, controls the switch of first switch SW 1; The output of the second NOR gate NOR2 is connected with second switch SW2, the switch of control second switch SW1.
This adaptive unit 7 is when work; When current comparator unit 4 produced signals power switch pipe P is turn-offed, rest-set flip-flop was controlled 1 conducting of first switch SW, second switch SW2 breaks off, and this moment, the first current source I1 gave capacitor C 2 chargings through first switch SW 1, the 3rd switch SW 3; After degaussing detecting unit 8 detects secondary winding Ns degaussing completion; Degaussing detecting unit 8 sends signal and controls that first switch SW 1 is broken off, second switch SW2 conducting for rest-set flip-flop, rest-set flip-flop, and this moment, capacitor C 2 was through the 3rd switch SW 3, first switch SW 1, second current source I2 discharge; The time of capacitor C 2 chargings is the time of secondary winding Ns degaussing; According to the current ratio of the first current source I1 and the second current source I2, just can confirm the discharge time of capacitor C 2, just adaptive unit 7 time of postponing automatically.The time of postponing automatically is to control through the ratio of setting, rather than the fixing scheduled time control, so can not cause error because of the difference of concrete system.When the voltage after capacitor C 2 discharge during less than reference voltage source VREF2; The output output high level of hysteresis comparator 9; And then make monostable flipflop 10 send pulse signal to switching signal generation unit 5; Switching signal generation unit 5 is through driver element 6 power controlling switching tube P conductings, and the 3rd switch SW 3 is turn-offed simultaneously.
The work wave of this LED constant-current drive circuit is as shown in Figure 3:
GD is said among power switch pipe grid voltage waveform such as Fig. 3; When the power switch pipe conducting; Primary current converts voltage into through sampling resistor; This voltage is sampled through sample holding unit, and when power switch pipe turn-offed, the peak current detection holding unit kept this voltage (shown in Vsh among Fig. 3).Turn-off T1 constantly at power switch pipe; Adaptive unit begins to calculate the degaussing time; At T2 constantly, degaussing finishes, and adaptive unit will be postponed a period of time automatically to the T3 moment; Hysteresis comparator 9 output switching activities trigger monostable flipflop 10 and produce positive pulse signal (shown in SHOT among Fig. 3), and control switch signal generation unit 5 produces the power switch pipe Continuity signal.The primary current waveform at T1 constantly, reaches maximum Ipk shown in Ip among Fig. 3; Secondary current waveform is shown in Is among Fig. 3.At T1 to T2 is secondary degaussing time T DEMAG in the time, is the degaussing time T DELAY of postponing in the time at T2 to T3, and the total turn-off time TOFF of power switch pipe is degaussing time and the degaussing time sum that postpones:
TOFF＝TDEAMG+TDELAY
Wherein: K*TDELAY=TDEMAG, K are the ratio of the second current source I2 and the first current source I1.
Provide the mathematical derivation formula that the control of former limit realizes constant current below:
The average current of LED of flowing through is:
Again
So
Wherein: VREF is a voltage reference
K is a current ratio coefficient in the adaptive unit
N is primary coil and secondary coil turn ratio
Rcs is a sampling resistor
Can be known that by above-mentioned formula when VREF, N, K and Rcs were given steady state value, Io also was a steady state value, the electric current of the LED that promptly flows through is a steady state value.
This circuit has the following advantages: 1) can realize LED constant current control, the useful life of improving LED; 2) do not use optocoupler, can overcome the problem of optocoupler CTR decay, improved the stability of circuit; 3) the power switch pipe switching frequency is frequency conversion, can greatly improve the distortion of EMI harmonic.4) adopt this circuit to simplify peripheral circuit greatly, application cost is reduced greatly.
More than a kind of LED constant-current drive circuit that the embodiment of the invention provided has been carried out detailed introduction; For one of ordinary skill in the art; According to the thought of the embodiment of the invention, the part that on embodiment and range of application, all can change, in sum; This description should not be construed as limitation of the present invention, and all any changes of making according to design philosophy of the present invention are all within protection scope of the present invention.
Claims (4)
1. LED constant-current drive circuit; Comprise transformer, switching signal generation unit, driver element; Said transformer comprises former limit winding, secondary winding and auxiliary winding, and said former limit winding is connected with the sampling resistor of a ground connection through a power switch pipe, and said switching signal generation unit is controlled the break-make of said power switch pipe through said driver element; Said secondary winding is connected with LED through current rectifying and wave filtering circuit; Said auxiliary winding and said secondary winding homophase is characterized in that this circuit also comprises:
The voltage reference unit is used to produce reference voltage;
The peak current detection holding unit is used for when the power switch pipe conducting, the voltage on the sampling resistor being sampled, and when power switch pipe turn-offs, exports the crest voltage of sampling gained;
Error amplifier unit, two inputs of said error amplifier unit are connected with the output of said voltage reference unit, the output of peak current detection holding unit respectively;
The current comparator unit; Its negative input end connects the output of said error amplifier; Positive input terminal connects sampling resistor; Output connects the input of said switching signal generation unit, and when the positive input terminal voltage of current comparator unit during greater than negative input end voltage, the output of current comparator unit produces signal and makes said switching signal generation unit drive said power switch pipe to turn-off;
The degaussing detecting unit is used to detect degaussing time of secondary winding;
Adaptive unit; Be used for the automatic following calculation secondary winding degaussing time; And in the ratio of the setting certain hour of postponing automatically; And then drive said switching signal generation unit and make the power switch pipe conducting, said adaptive unit is connected with said degaussing detecting unit, switching signal generation unit, current comparator unit output.
2. LED constant-current drive circuit according to claim 1; It is characterized in that: said auxiliary winding one end is connected with first divider resistance; The other end of said first divider resistance is connected with second divider resistance and degaussing detecting unit respectively, and the other end ground connection of said second divider resistance also is connected with the other end of auxiliary winding.
3. LED constant-current drive circuit according to claim 1; It is characterized in that: said adaptive unit comprises first current source, second current source, first switch, second switch, the 3rd switch, electric capacity, rest-set flip-flop, hysteresis comparator and monostable flipflop; Said first current source is connected with the 3rd switch through first switch; Said second current source is connected with the 3rd switch through second switch; The other end of said the 3rd switch is connected with the positive input terminal of electric capacity and hysteresis comparator, said capacity earth, and the negative input end of said hysteresis comparator is connected with a reference voltage source; The output of said hysteresis comparator is connected with the input of said monostable flipflop; The output of said monostable flipflop is connected with said switching signal generation unit, and two inputs of said rest-set flip-flop are connected with the output and the degaussing detecting unit output of current comparator unit respectively, and two inputs of said rest-set flip-flop are connected with first switch, second switch respectively; Said the 3rd switch turn-offs when said power switch pipe conducting, conducting when said power switch pipe turn-offs.
4. LED constant-current drive circuit according to claim 3; It is characterized in that: said rest-set flip-flop comprises first NOR gate; Second NOR gate; One input of said first NOR gate connects the output of said current comparator, and another input of said first NOR gate connects the output of second NOR gate; One input of said second NOR gate connects the output of degaussing detecting unit; Another input of said second NOR gate connects the output of first NOR gate; The output of said first NOR gate is controlled said first switch, and the output of said second NOR gate is controlled said second switch.
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| CN103472288A (en) * | 2013-08-30 | 2013-12-25 | 西北工业大学 | Peak voltage detection circuit |
| CN103781234A (en) * | 2012-10-19 | 2014-05-07 | 瑞鼎科技股份有限公司 | Light emitting diode driving device with holding current circuit and operation method thereof |
| CN104135790A (en) * | 2014-06-11 | 2014-11-05 | 普诚科技（深圳）有限公司 | LED (Light-emitting Diode) dimming control circuit |
| CN105007658A (en) * | 2015-07-23 | 2015-10-28 | 宁波拓扑思科电子科技有限公司 | Peak current detection circuit of three-pin critical mode LED driver chip and application thereof |
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| CN103781234A (en) * | 2012-10-19 | 2014-05-07 | 瑞鼎科技股份有限公司 | Light emitting diode driving device with holding current circuit and operation method thereof |
| CN103781234B (en) * | 2012-10-19 | 2016-06-01 | 瑞鼎科技股份有限公司 | Light emitting diode driving device with holding current circuit and operation method thereof |
| CN103472288A (en) * | 2013-08-30 | 2013-12-25 | 西北工业大学 | Peak voltage detection circuit |
| CN104135790A (en) * | 2014-06-11 | 2014-11-05 | 普诚科技（深圳）有限公司 | LED (Light-emitting Diode) dimming control circuit |
| CN105142260A (en) * | 2014-08-12 | 2015-12-09 | 杭州士兰微电子股份有限公司 | LED driving circuit applicable to silicon controlled rectifier light modulator, and control circuit thereof |
| CN105142260B (en) * | 2014-08-12 | 2017-10-13 | 杭州士兰微电子股份有限公司 | LED drive circuit and its control circuit suitable for controllable silicon dimmer |
| CN105007658A (en) * | 2015-07-23 | 2015-10-28 | 宁波拓扑思科电子科技有限公司 | Peak current detection circuit of three-pin critical mode LED driver chip and application thereof |
| CN105007658B (en) * | 2015-07-23 | 2017-11-28 | 宁波拓扑思科电子科技有限公司 | The peak current detection circuit of three pin critical conduction mode LED drive chips and its application |
| CN105792433A (en) * | 2016-04-19 | 2016-07-20 | 深圳市明微电子股份有限公司 | Switch power driving chip and silicon controlled rectifier dimmer LED drive circuit |
| CN105792433B (en) * | 2016-04-19 | 2017-08-25 | 深圳市明微电子股份有限公司 | Switching Power Supply driving chip and controllable silicon light modulation LED drive circuit |
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Application publication date: 20120919 |