One kind is used for high power factor LED drive power switching frequency limiting circuitTechnical field
Driven the present invention relates to a kind of switching power circuit, more particularly to a kind of high power factor type switching power LED that is used forSwitching frequency limiting circuit during dynamic power supply light modulation.
Background technology
With the development of LED illumination, the demand of intelligent lighting is increasing, so application scenarios also day of LED light modulationsCrescent is different, but occurring LED current to drop to after a certain size in the application process of many light modulations can not just continue downwardsThe problem of regulation, so as to result in, dimming scope is narrow, and Consumer's Experience effect is poor.
Fig. 1 is traditional High Power Factor Boost topology constant current driver circuit for LED, is generally included：Rectifier bridge D1~D4, it is defeatedEnter high-frequency filter capacitor C1, demagnetization detection resistance R3, output capacitance C2, control chip U1, peak point current sampling resistor R1, powerSwitching tube Q1, inductance L1, sustained diode 5, output current sampling resistor R2 and LED load LEDs.In control chip U1Portion, is generally included：Demagnetization detection unit, benchmark ＆ builtin voltage units, constant-current control unit simulates dimming unit, current sampleUnit, error amplifier, peak point current sampling unit and logic ＆ driver elements.
The principle and limitation of tradition application, the low-power LED driving power source system for using Boost topology, in order toObtain high power factor, it will usually constant current output is realized using the averagecurrent mode control of critical conduction control, works as needsAdjust output current ratio if desired for electric current to reduce, then the benchmark of error amplifier will reduce, and cause the peak for flowing through inductance L1Be worth electric current to decline, power tube Q1 grid opening time Ton reduces, erasing time of inductance also can equal proportion decline, systemSwitching frequency increase, after the power tube that is equal to switching power source chip inner setting when the Ton times minimum ON time, Ton is by nothingMethod continues to lower, so electric current can not also decline, and due to the increase of switching frequency, the switching loss of system can also increase,Reduce efficiency.
The content of the invention
For the limitation of the conventional high power factor Switching Power Supply LED output current control technologies dimmed, the present invention is publicA kind of switching frequency limiting circuit for high power factor LED drive power is opened, the switching frequency limiting circuit includes：OneBenchmark and builtin voltage unit, for producing required output current reference voltage；One demagnetization detection unit, for detecting inductanceErasing time, inductive current zero passage is detected；One constant-current control unit, for allowing output current to keep constant；One peak valueCurrent detecting unit, for the magnitude of voltage on peak point current sampling resistor to be compared with chip internal reference voltage, to limitMaximum current peak processed, a dimming unit, the size for regulating system output current；One dimming unit, for light modulation to be believedNumber change into the voltage signal of simulation；One current sampling unit, the ohmically voltage of output electric current measure is flowed through for detecting, andThe voltage that the voltage and dimming unit are produced is superimposed, and then the sampled signal is exported to error amplifier；One error is putBig device unit, the signal for current sampling unit to be exported follows reference signal, while the error signal of amplification is fed back toOpen time delay and constant-current control unit；One open time delay unit, for allowing what the output of error amplifier block dynamic regulation was openedTime；One logic ＆ driver elements, the switch drive for realizing system power pipe.
Further, the present invention discloses a kind of constant current driver circuit for LED, the constant current driver circuit for LED includes：One rectifier bridge, an input filter capacitor, a demagnetization detection resistance, a peak point current sampling resistor, a power tube, an inductance, oneFly-wheel diode, an output capacitance, a current sense resistor, a LED load.
Further, the fault in enlargement signal that the input put-into error amplifier output of open time delay unit is produced,And the switch controlling signal Ton of power tube, power output pipe open instruction signal TURN_ON.
Further, the open time delay unit includes：One rising edge trigger pulse generation circuit unit, for wheneverOutput logic signal by it is low turn high when produce a positive impulse level；One amplifier unit；One NMOS tube；FirstPMOS；Second PMOS；3rd PMOS；4th PMOS；One resistance；First switch；Second switch；3rd switch；First electric capacity；Second electric capacity；One fixed constant-current source；One comparator unit；First nor gate；Second nor gate；3rd orNOT gate.EA_CTRL signals connect the normal phase input end of amplifier unit, the source and resistance of the negative input termination NMOS tube of amplifier unitOne end is connected, the grid of the output termination NMOS tube of amplifier；The drain terminal of NMOS tube connects the drain terminal of the first PMOS, the grid of NMOS tubePole connects the output end of amplifier, and the source of NMOS tube is connected with one end of the reversed-phase output of amplifier and resistance；One end of resistanceIt is connected with the source of NMOS tube and the end of oppisite phase of amplifier, the other end of resistance is connected with microarray biochip；First PMOS sourceEnd is connected with chip internal supply voltage VDD, the drain electrode and second that the first PMOS grid and drain electrode are connected simultaneously with NMOSPMOS grid is connected；2nd PMOS source is connected with chip internal supply voltage VDD, the 2nd PMOS grid and firstPMOS grid is connected with drain electrode to be connected with NMOS drain electrode simultaneously, the 2nd PMOS drain electrode and one end of first switch and theOne end of one electric capacity is connected with the inverting input of comparator unit；One end of first switch and the 2nd PMOS drain electrode and theOne end of one electric capacity is connected with the inverting input of comparator unit, and the other end of first switch is connected with chip；First electricityOne end of appearance is connected with one end of first switch and the 2nd PMOS drain electrode and the inverting input of comparator unit, the first electricityThe other end of appearance is connected with chip；3rd PMOS source is connected with chip internal supply voltage VDD, the 3rd PMOS gridIt is connected with drain electrode and is connected simultaneously with one end of fixed constant-current source and the 4th PMOS grid；One end and the 3rd of fixed constant-current sourcePMOS grid is connected with the grid of drain electrode and the 4th PMOS, and the other end of fixed constant-current source is connected with chip；4thPMOS source is connected with chip internal supply voltage VDD, and the 4th PMOS grid and the first PMOS grid are connected with drain electrodeOne end with fixed constant-current source is connected simultaneously, and the 4th PMOS drain electrode is connected with one end of second switch；One end of second switchIt is connected with the 4th PMOS drain terminal, the other end of second switch and one end of the second electric capacity and the 3rd one end switched and is comparedThe positive input of device unit is connected；One end and one end of second switch and one end of the second electric capacity of 3rd switch and comparedThe positive input of device unit is connected, and the other end of the 3rd switch is connected with chip；One end of 3rd electric capacity and the 3rd switchOne end and second one end of switch is connected with the positive output end of comparator unit, the other end and chip of the 3rd electric capacityGround is connected；One end of the drain terminal and first switch of the inverting input of comparator unit and the second PMOS and the first electric capacityOne end is connected, one end of the drain terminal and second switch of the positive input of comparator unit and the 4th PMOS and the second electric capacityOne end be connected, the output end of comparator unit is connected with an input of the first nor gate；One input of the first nor gateIt is connected with the output end of comparator, another input of the first nor gate is connected with input signal end Tdem, the first nor gateOutput end is connected with an input of the second nor gate；One input of the second nor gate and the output end phase of the first nor gateEven, another input of the second nor gate is connected with the output end of the 3rd nor gate, the output end of the second nor gate and the 3rd orOne input of NOT gate is connected, the output end output signal TURN_ON of the second nor gate；One input of the 3rd nor gate andThe output end of two nor gates is connected, another input of the 3rd nor gate and the output of rising edge trigger pulse generation circuit unitEnd signal Tp is connected, and the output end of the 3rd nor gate is connected with an input of the second nor gate；Rising edge trigger pulse is producedThe input of circuit unit is connected with Ton signals, the output end signal Tp of rising edge trigger pulse generation circuit unit control theOne switch is connected with an input of the 3rd nor gate simultaneously with the opening and closing of second switch.
Compared with traditional high power factor LED light modulations drive control circuit, use the system of circuit of the present invention can be withThe light modulation of wider range is realized in the case where not sacrificing power factor (PF), while tune when ensure that output current very littleActinic degree, Consumer's Experience is more preferable, and system is more safe and reliable, and efficiency when low current is exported is with height.
Brief description of the drawings
It can be obtained further by following detailed description of the invention and institute's accompanying drawings on the advantages and spirit of the present inventionSolution.
Fig. 1 is traditional booster type constant current driver circuit for LED with dimming function；
Fig. 2 is the booster type constant current driver circuit for LED with dimming function for having used circuit of the present invention；
Fig. 3 implements for circuit of the present invention；
Fig. 4 is traditional control signal key point waveform；
Fig. 5 is the control signal key point waveform of circuit of the present invention；
Embodiment
The specific embodiment of the present invention is described in further detail below in conjunction with the accompanying drawings.
The present invention solves the control chip work for the output current control technology for being traditionally used for LED drive power light modulationThere is provided the control circuit for solving the problem the problem of proportional increase with the reduction of output current reference voltage for frequency.Pass throughThe method that reduction output current reference voltage is combined with the opening time of control system, the work frequency of LED drive powerRate control in a suitable scope, effectively solve traditional output current control technology dim when working frequency intoThe problem of ratio increases, and work(power factor (PF) is not influenceed.
With reference to Fig. 1 analyses, Fig. 1 gives traditional booster type LED constant current light adjusting system, current sample module collection electric currentThe voltage of detection resistance, the peak point current of inductance is flowed through with regulation by the negative feedback control of error amplifier, in order thatSystem possesses high power factor, and system is usually operated at the pattern that critical conduction and power tube Q1 ON times are fixed, inputElectric current is expressed as follows：
Wherein IIN is system input current, and VINsinwt is input voltage, usually sinusoidal signal, and Ton is power tubeON time, L is the sensibility reciprocal of inductance pair.It can see from above formula and given condition, if the Ton times are constant, then defeatedEntering electric current will keep and the same phase of input voltage, and be sinusoidal signal, and generally system can possess very high power in such casesFactor.
Wherein ILED is output current, and f is system switching frequency meter, and ILP is inductance peak point current, from above formula, ILPSmaller, frequency is higher, and when the opening time of system power pipe the minimum opening time of system specialization is less than, frequency is by nothingMethod increase, dimming scope is limited.
Can be while limiting system when output current very little so going for that preferable dimming effect just has toSwitching frequency, can just widen dimming scope, but also require that system possesses high power factor (PF) simultaneously, then require systemIt is the sinusoidal waveform with input voltage with phase that input current is met when light modulation.
Further, the system switching cycle must with electric discharge erasing time of the ON time of power tube and inductance itWith it is proportional：
Wherein fnew is to have used the power tube switching frequency after circuit of the present invention, and Tdem is inductive current demagnetization in systemTime, K is open time delay proportionality coefficient, is the parameter that error amplifier is controlled in system, and power tube ON timeAnd the electric discharge erasing time sum of inductance is related.
The input current of system is：
Wherein IINnew is the input current for having used system after circuit of the present invention, and its input waveform is similarly and inputted electricityPress the sine wave of same-phase, it is ensured that the power factor (PF) of system.
Fig. 2 is application of the circuit of the present invention in boosting Dimmable LED driving power supply, and wherein systematic difference circuit includesThe electric capacity 201 of input rate high-frequency noise, system inductance 202, inductance erasing time detection resistance 203, switching power tube 204, electricityFeel peak point current sampling resistor 205, fly-wheel diode 206, output filter capacitor 207, demagnetization detection unit 208, current constant controlUnit 209, dimming unit 210, logic ＆ driver elements 211, open time delay unit 212, peak current detection unit 213, errorAmplifier unit 214, current sampling unit 215, benchmark ＆ builtin voltages unit 216 and current sense resistor 217.
Wherein 212 be circuit of the present invention, and the principle of the circuit is to receive control signal by 214 output and produce to prolong all the wayWhen the time control the unlatching of power tube 204, open time delay Proportional coefficient K reduces when LED current increase is exported, when defeatedWhen going out electric current reduction, open time delay proportionality coefficient increase so that in the case of output current very little, used the present inventionThe switching frequency of system of the system of circuit than circuit of the present invention is not used is low.
Fig. 3 implements for an open time delay circuit in the present invention, and its purpose is to realize the process of light modulationThe switching frequency of middle reduction system so that switch periods and power tube 204 ON time and the erasing time of inductance 202Equal proportion changes, and includes an amplifier unit 314, a NMOS tube 305, a current sampling resistor 316, a pair in circuitConstitute the PMOS301 and 302 of current mirror, a switch 308, an electric capacity 309, a pair PMOS303 of current mirror and 304, one each otherRoad fixed current source, two perfect switches 306 and 307, an electric capacity 310, a comparator unit 311, the one or two input He of nor gate 312One inputs the rest-set flip-flop 313 that nor gates are constituted, a rising edge trigger pulse generation circuit 317 by two.
The positive input terminal that control signal EA_CTRL control signals control amplifier 314 is produced in error amplifier block 214,The conversion of voltage verses current is realized by the LDO circuit of 314,305 and 316 compositions, is made up of current mirror 301 and 302Circuit to 309 charge, the charge cycle run through whole switch periods, every time 204 open moments can by 317 produce all the wayShorter pulse times to reset to 309, and when LED current is big, EA_CTRL is raised, and the charging current I1 on 309 is increased, and 309The upper voltage rate of rise is big.Otherwise charging current reduces, raised voltage slope is small on 309.In power tube opening time and inductanceIn the demagnetization Ton+Tdem times, the constant current I2 that the current mirror being made up of 315 and 303 and 304 is produced can charge to 310,The voltage is maintained in 310 within the Ton+Tdem times to opening time next time, has Tp controlling switches 308 to reset, 312One end access Ton+Tdem signals avoid open signal from being stored in rest-set flip-flop too early.Every time power is produced when Vcn ＞ VcpThe open signal of pipe 204, now open time delay proportionality coefficient：
From above formula, when EA_CTRL is higher, I1 is bigger, and K is smaller, otherwise K bigger, can be very good by the circuitThe dimming effect of improvement system, system switching frequency when reduction low current, while not influenceing the power factor (PF) of system.
Described in this specification is only the preferably embodiment of the present invention, the technical side for illustrating the present inventionCase, rather than limitation of the present invention, all those skilled in the art according to the present invention design by logic analysis, reasoning orLimited experiment is come technical scheme obtained from some adjustment are made that to the present invention and are changed, such as by the output electricity of the present inventionThe technology of flow control circuit is applied in switch-segment light modulation, PWM light modulations, in the LED drive power of simulation light modulation etc..Still it is this hair, all should be within the scope of the present invention where bright main idea.