CN1553557A - Power factor correcting circuit and method with frequency control - Google Patents

Abstract

A PFC circuit comprises: a latch having an output end responding to a clock signal jump current along with start coil for generating PPC signal, a control signal received by input end; the current modulation circuit having a first input end used in receiving PFC signal to build the charging time for coil current, a second input end used in checking the coil current to build the duty cycle for coil current at one period of clock signal, and a output end providing a control signal as a function of the charging time and the duty cycle.

Description

Frequency controlled circuit of power factor correction and method

Technical field

Relate generally to integrated circuit of the present invention, and, more particularly, relate to integrated circuit of power factor correction.

Background technology

Integrated power factor correction (PFC) circuit is a kind of like this change-over circuit, its guarantee with homophase, be that the electric current of sine loads on interchange (AC) circuit basically.If there is not PFC to proofread and correct, many electrical systems can only extract electric current from the alternating current circuit voltage near the crest voltage level of alternating current circuit.Can make alternating current circuit voltage produce distortion with big electric current and other times with the building-up effect that zero current loads the alternating current circuit at the voltage peak place.In addition, there is not the system of PFC may in the three-phase distribution net, cause big neutral current to flow.For fear of these problems, so that make electric equipment carry out work well, the power distribution network of the electric company in zone must have nargin, and this just needs big fund input.Some government's instructions must be included PFC in the employed power supply of some or all electric equipment.

Pfc circuit is typically by inductor or coil, switches electric current from the alternating current circuit with the frequency that is much higher than the alternating current circuit frequency, so that make coil magnetizing or charging.For example, when the alternating current circuit frequency was 50Hz, system may use the inversion frequency of 100kHz at least.The energy that is stored in the coil is released among the capacitor, so that produce PFC direct current (DC) voltage of a centre, comes to electric equipment or system's power supply.For the alternating current that obtains being essentially sinusoidal, order follows the current voltage of alternating current circuit to be directly proportional by the electric current that coil is switched at the mean value of a change-over period.Consequently provide high effective power factor for the alternating current circuit.

Most of previous pfc circuits work in the self-excitation mode, wherein, in case stored coil current has been released to the capacitor there in the previous cycle, just have an electric current to be switched, so that coil is charged.Consequently, the switching frequency of previous various pfc circuits changes along with the load current of current alternating current circuit voltage and this system.Variable like this inversion frequency is difficult to filtering, with the electromagnetic interference that suppresses or removal is produced by the switching coil electric current.Such filtering needs the filter of various complexity, and they are loss power not only, and the manufacturing cost of a system is increased.

Therefore, need and a kind ofly run on fixed frequency or,, keep the low manufacturing cost of pfc circuit simultaneously so that reduce the electromagnetic interference of system near pfc circuit fixed frequency, that be used for correcting power factors and method.

Description of drawings

Fig. 1 is a schematic diagram of power factor correction (PFC) circuit;

Fig. 2 is a sequential chart, the various waveforms of expression pfc circuit;

Fig. 3 is a schematic diagram of the duty cycle transducer of pfc circuit;

Fig. 4 is a schematic diagram of the current modulator of pfc circuit; And

Fig. 5 is the schematic diagram of the current modulator in an alternative embodiment.

Embodiment

In all accompanying drawings, the parts with same reference number have similar function.

Fig. 1 is a schematic diagram of power factor correction (PFC) circuit 100 controlled by PFC control circuit 10, and this pfc circuit comprises diode bridge 20, resistor 22-24, inductor or coil 25, diode 26, output capacitor 27, time capacitor 28, and switching transistor 29.Pfc circuit 100 receives a sinusoidal voltage VAC from exchanging (AC) circuit, and produces a direct current (DC) PFC output signal V at a node or output 30 _OUTIn one embodiment, pfc circuit 100 plays the effect of a boost conversion pressurizer, and it receives, and numerical value is about 220V root-mean-square value (RMS) and frequency is about the VAC of 50Hz, and produces the PFC output voltage V that numerical value is about direct current 400V _OUTIn certain areas, VAC has the frequency that is about 110V (RMS) and 60Hz.VAC has typical excursion approximately ± 20%.

Diode bridge 20 is full wave bridge rectifiers of a standard, and it carries out rectification to line voltage distribution VAC, and the sine voltage V after rectification of node 32 outputs _IN, its frequency is that the twice of the frequency of VAC is about 100Hz, its peak value is about 310V.Can be on diode bridge 20 capacitor (not shown) of cross-over connection, to reduce the VAC noise peak.

Coil 25 has the inductance that representative value is L=100.0 μ H, and low equivalent series resistance, so that realize high efficiency operation.

Transistor 29 is big electric current n NMOS N-channel MOS N field-effect transistors, and it switches on and off the coil current I by coil 25 _COILIn one embodiment, transistor 29 is power transistors, and it can switch the coil current I greater than 2A _COILPeak value.These electric currents are less near the zero cross point of VAC the time, and bigger near the VAC voltage peak time.Transistor 29 typically has the bigger grid capacitance greater than 500pF.

Coil current I _COILA charging current component I is arranged _CHAnd discharging current component I _DSCHWhen transistor 29 conductings, charging current I _CHFlow through coil 25, magnetic energy is stored among the coil 25.When transistor 29 ends, along with discharging current I _DSCHFlow to capacitor 27 from coil 25 by diode 26 magnetic energy of being stored is discharged, on node 30, produce PFC voltage V _OUT

Coil current I _COILReturn path by resistor 22 arrival diode bridges 20 is arranged, and it produces a current sense voltage V on node 31 _IS, with monitoring I _COILWhen flow.In one embodiment, resistor 22 has the resistance of about 0.2 Ω, therefore, works as I _COILSize when being 1A, V _ISNumerical value be about-0.2V.Alternatively, working voltage sensing technology, rather than current sense technology shown in Figure 1, also energy measurement I _COILON time.For example, coil 25 can constitute the elementary winding of a transformer, and this Secondary winding of transformer has a terminal typically to be coupled to the input of duty cycle transducer 12, the other end ground connection of secondary winding by a resistor at node 31.Work as I _COILWhen charging, the current sense voltage V that secondary winding produces _ISBe positive voltage, work as I _COILWhen discharging, V _ISBe negative voltage, and work as I _COILBe 0 o'clock, V _ISBe essentially 0V.

I _COILSize be the PFC output voltage V _OUTA function, and the feedback of the voltage divider by constituting V by resistor 23 and 24 _OUT, control I _COILSize.This voltage divider is to V _OUTSample, and provide a sensing voltage V at node 36 _SENSE Resistor 23 and 24 has resistance R respectively ₂₃And R ₂₄

PFC control circuit 10 comprises 14, one triggers of 12, one current modulators of a duty cycle transducer or latch 16, and an output buffer 18.Current modulator 14 produces a regularly electric current I _TIMING, it charges to external capacitor 28, to set up a timing voltage V _TIMING, in order to control charging current I _CHCycle, and control its peak amplitude thus, this will be illustrated below.In one embodiment, in a block semiconductor substrate, form PFC control circuit 10, as integrated circuit.

Output buffer 18 is non-inverting amplifiers of a standard, and the big capacity load that is provided by transistor 29 can be provided for it.

Latch 16 is R-S triggers of a standard, and it has a Q output, and digital switching signal VSW is provided, and VSW is set at the place, hopping edge of a clock signal C LOCK, and is reset at the place, hopping edge of a digital termination signal TERM.In order to obtain high power factor, CLOCK preferably is operated in one and is far longer than V _INOn the frequency of frequency.In one embodiment, V _INFrequency with about 100Hz, perhaps the cycle of about 10ms, the frequency controlled or substantial constant according to about 100kHz in the cycle of perhaps about 10 μ s, produces the CLOCK pulse.When VSW is set, make transistor 29 conductings by output buffer 18, thus the actuating coil electric current I _COILCharging component I _CH, make coil 25 magnetization or stored energys.When VSW is reset, makes transistor 29 end by output buffer 18, thereby stop charging component I _CH, start I simultaneously _COILDischarge component I _DSCH, it flows through diode 26, and energy is transferred to capacitor 27 from coil 25.

12 couples of coil current I of duty cycle transducer _COILMonitor, and produce a digital line loop current transducing signal COILON, work as I at output 34 places _COILWhen being essentially nonzero value, it is in logic high, and works as I _COILBe 0 o'clock, it is in logic low.A comparator is with current sensing signal V _ISWith reference signal V _REF2Compare, to produce COILON.In one embodiment, duty cycle transducer 12 comprises a preamplifier, and it increases V _ISAmplitude, to improve noise immunity.Because VSW is set when each CLOCK pulse arrives, the beginning in a new cycle of expression is so at a CLOCK in the cycle, COILON is in the part of logic high and just represents I _COILDuty cycle.

Current modulator 14 has an input at node 36 places, and it is by transducing signal V _SENSEMonitor PFC signal V _OUT, so that be coil current I _COILLive part I _CHSet up a time T _CHAt node 34 places, an input detects I _COILWhen flow through, so that digital signal COILON to be provided, thereby set up I _COILIn the duty cycle of a CLOCK on the cycle.Current modulator 14 comprises an error amplifier, and it is between V _SENSEWith reference voltage V _REF1Between difference amplify so that produce correction signal V _ERR, in order to set I _COILSize and time T _CHDifference of having amplified and COILON carry out integration on the one-period of CLOCK, so that produce termination signal TERM on an output of node 38, to stop charging current I _CH, and start discharging current I _DSCHThereby TERM is as T _CHAnd a function of duty cycle is produced.In one embodiment, TERM is produced like this, makes T _CHAnd I _COILThe product of duty cycle keep a constant.

The change-over period of PFC control circuit 10 is started by clock signal C LOCK, above-mentioned clock signal preferably be operated in one constant or near on the constant frequency.Because the cycle of CLOCK is much smaller than V _INCycle, so when transistor 29 conductings, the voltage V of a substantial constant just occurs at coil 25 two ends _INCoil current I _COILApproximate V greatly according to one _INThe slope of/L increases linearly, and therefore, its peak value is I _PEAK=T _CH* V _IN/ L, in the formula, T _CHBe charging current I _CHDuration.Similarly, discharging current I _DSCHSlope be approximately equal to (V _OUT-V _IN)/L, and its duration T _DSCH=L*I _PEAK/ (V _OUT-V _IN).Therefore, I _COILFor whole cycle of nonzero value is provided by equation 1,

$T_{\mathrm{COIL}}=T_{\mathrm{CH}}+T_{\mathrm{DSCH}}=L\·I_{\mathrm{PEAK}}\·\frac{V_{\mathrm{OUT}}}{V_{\mathrm{IN}}\·(V_{\mathrm{OUT}}-V_{\mathrm{IN}})}.---1)$

As can be seen, at a clock cycle T _CLOCKOn average line loop current I _{COIL_CLOCK}Provide by equation 2,

$I_{\mathrm{COIL}\_\mathrm{CLOCK}}=\frac{V_{\mathrm{IN}}\·T_{\mathrm{CH}}}{2\·L}\·\frac{(T_{\mathrm{CH}}+T_{\mathrm{DSCH}})}{T_{\mathrm{CLOCK}}}=\frac{V_{\mathrm{IN}}}{2\·L}(T_{\mathrm{CH}}\·D_{\mathrm{CYCLE}})---2)$

In the formula, D _CYCLE=(T _CH+ T _DSCH)/T _CLOCKAs average line loop current I _{COIL_ CLOCK}Follow V _INRectification after sinusoidal waveform the time (if T _CH* D _CYCLEKeep constant and this situation will occur), just can obtain high power factor.

With reference to Fig. 2, can see the working condition of PFC control circuit 10, this is a sequential chart, some chosen waveforms of expression PFC control circuit 10.Beginning in time T 0, is supposed clock signal C LOCK, switching signal VSW, and termination signal TERM and current sensing coil signal COILON are in low level.Suppose coil current I further _COIL, current sense voltage V _IS, the timing electric current I _TIMINGAnd timing voltage V _TIMINGRespectively equal zero.

In time T 1, the hopping edge from low to high of CLOCK signal makes latch 16 impel the saltus step from low to high of VSW, makes transistor 29 conductings by buffer 18, with the actuating coil electric current I _COILBe noted that the I that begins to flow in time T 1 _COILComponent be charging current I _CHBecause the cycle of CLOCK is much smaller than V _INCycle, and the voltage drop on transistor 29 is very little typically, so the voltage V of a substantial constant _INBe applied to the two ends of coil 25, make I _COILIncrease linearly or according to shown in the figure with V _INThe slope of/L forms sawtooth waveforms.I _COILFlow through resistor 22, produce current sense voltage V _IS, it also increases linearly, but along the direction of negative voltage, as shown in the figure.VSW saltus step from low to high is changed to high level with COILON, to start regularly electric current I _TIMING, the latter charges to capacitor 28, so that set up timing voltage V according to the mode of linear saw-tooth wave _TIMING

At time T 2, V _TIMINGArrive a threshold voltage, make termination signal TERM generation saltus step from low to high, the latter resets latch 16.This threshold voltage can be a predetermined voltage or a variable voltage, and this will be described in detail below.The saltus step from high to low of VSW stops I _COILCharging current I _CHAnd startup discharging current I _DSCH, so that energy is transferred to capacitor 27 from coil 25.VSW also makes a switch closure, makes capacitor 28 discharges, and with I _TIMINGBe diverted to ground, so that with V _TIMINGBe reduced to 0, as shown in the figure.I _DSCHAccording to slope (V _OUT-V _IN)/L reduces with linear mode, up to being stored in till magnetic energy among the coil 25 discharged fully.

At time T 3, I _COILBe reduced to 0.Current sensing signal V _ISAlso be increased to 0 linearly, it makes current sensing coil signal COILON produce a saltus step from high to low.The remainder of clock cycle before time T 4 (at this moment beginning next cycle), I _COILBasically keep null value.

Fig. 3 represents to be connected to a schematic diagram of the duty cycle transducer 12 of resistor 42, comprises amplifier 44, comparator 45, latch 46 and resistor 42-43.Duty cycle transducer 12 receives transducing signal V at node 31 by resistor 42 _IS, with monitoring coil current I _COILFlow.An output is connected to node 34, to produce current sensing coil signal COILON, works as I _COILValue be essentially at 0 o'clock, the value of COILON is a logic low, works as I _COILBe at non-0 o'clock, the value of COILON is a logic high.

In time T 1, the saltus step switching signal VSW of clock signal C LOCK from the logic low to the high level is set to logic high numerical value, with the actuating coil electric current I _COILLatch 46 is provided with like this, makes COILON produce logic level saltus step from low to high at node 34 places, with expression I _COILFlow, that is, have non-0 value.Simultaneously, transducing signal V _ISBe reduced to a negative numerical value from 0 linearity.

Amplifier 44 and resistor 42-43 play the effect of gain stage, and it is to V _ISAmplify, to increase the noise immunity of system.In one embodiment, resistor 43 has the numerical value of about 10k Ω, and resistor 42 has the numerical value of about 1k Ω, and this makes that the numerical value of the signal that is exaggerated is about (10*V at node 41 places _IS).Therefore, before time T 2, the current potential of node 41 is increased to a positive potential linearly from 0, and in time T 2, along with coil 25 discharges, its numerical value begins to descend towards 0V.When being reduced to one, the current potential of node 41 is lower than V _REF2Numerical value the time, comparator 45 makes reset signal V _RProduce the saltus step from the logic low to the high level, it resets latch 46, and to make COILON generation saltus step from high to low, it represents I _COILDischarge into 0 basically.In fact, can be with V _REF2Be set to a little positive non-zero values, to avoid oscillatory regime occurring in comparator 45, the latter can be incorporated into V with noise effectively _RAmong.In one embodiment, V _REF2Be set to 0.1V, it is corresponding to I _COILThe numerical value of=0.05A.

Fig. 4 is an a schematic diagram of representing current modulator 14 in more detail, comprises amplifier 47-48, comparator 49, switch 50-51, resistor 52-53, capacitor 54-55 and current source 56.Resistor 52 and 53 has resistance R respectively ₅₂And R ₅₃, capacitor 54 and 55 has capacitance C respectively ₅₄And C ₅₅

Amplifier 47 plays the effect of error amplifier, and it is with transducing signal V _SENSEWith reference voltage V _REF1Compare, and their difference is amplified, thereby produce correction signal V at node 72 places _ERRIn fact, 47 pairs in amplifier is between desired value V _OUT=V _REF1* (1+R ₂₃/ R ₂₄) and V _OUTActual current numerical value between difference amplify.PFC control circuit 10 is by making V _SENSEKeep being substantially equal to V _REF1, regulate V effectively _OUT Capacitor 54 and resistor 23-24 play the effect of integrator or low pass filter, and its filtering may appear at PFC signal V _OUTAmong, at V _SENSEIn 100Hz or the ripple of 120Hz, the frequency of ripple depends on the frequency of the VAC local or zone.Capacitor 54 and resistor 23-24 produce an integration time constant R ₂₃* R ₂₄* C ₅₄/ (R ₂₃+ R ₂₄), it can be decayed and have the V of short duration _SENSEFluctuation.In one embodiment, this time constant is V at least _IN5 times of cycle for example, are worked as V _INCycle when being 10ms, this time constant is set to 50ms at least.Therefore, at a V _INIn cycle, V _ERRIt is constant to be considered to substantial constant.

In gain stage 70, correction signal V _ERRBy effectively divided by I _COILDuty cycle, this gain stage 70 contains amplifier 48, resistor 52-53, capacitor 55 and switch 50.Gain stage 70 plays the effect of integrator, and its time constant is set by resistor 52-53 and capacitor 55, in order to the conversion transient signal of filtering appearance when switch 50 turns on and off according to the frequency of clock signal C LOCK.The numerical value of above-mentioned time constant preferably is equal to or greater than 5 times of cycle of CLOCK.For example, if the cycle of CLOCK is 10 μ s, then the time constant of resistor 52-53 and capacitor 55 preferably should be 50 μ s at least.Control or threshold signal V are provided at node 74 places _TON

The running of gain stage 70 is as follows.When COILON is in high level, for example from time T 1 to time T3 (I _COILBe nonzero value), switch 50 is in open-circuit condition.V _ERRPlay the effect of reference voltage, it is connected to the non-inverting input of amplifier 48.And V _TONThen be connected to inverting input, both difference (V by resistor 52 and 53 _ERR-V _TON) usefulness time constant T _SW0=C ₅₅* (R ₅₂+ R ₅₃) carry out integration.When COILON is in low level, for example from time T 3 to time T4 (I _COILBe null value), switch 50 is in closure state, and is approximately 0 across the voltage at switch 50 two ends.The voltage that is essentially 0V this moment is applied to the inverting input of amplifier 48 by resistor 52.V _ERRStill act on the non-inverting input of amplifier 48, difference (V as reference voltage _ERR-0.0V) use integration time constant T _SW1=C ₅₅* R ₅₂Carry out integration.Because selected resistor 53 is more much smaller than resistor 52,, can think T approx so, can both produce the time constant that equates basically no matter which kind of position switch 50 is in _SW0=T _SW1Time constant T _SW0And T _SW1Preferably be selected as bigger than cycle of CLOCK so that a time-weighted average voltage V occurs at the inverting input of amplifier 48 _TON* (T3-T1)/(T4-T1)=V _TON* D _CYCLE, D here _CYCLE=(T3-T1)/(T4-T1), be I _COILIn the duty cycle of a CLOCK in the cycle.100 couples of V of pfc circuit _OUTEach input V of having guaranteed at amplifier 48 of adjusting _ERR=V _TON* D _CYCLEPerhaps V _TON=V _ERR/ D _CYCLEBecause V _ERRAt a CLOCK is invariable basically in the cycle, so product V _TON* D _CYCLEAlso be invariable, thereby make I _COILHave sinusoidal waveform, make pfc circuit 100 have high power factor simultaneously.

V _TIMINGBe by using constant current I _TIMINGCapacitor C28 charged to be produced, so it has jagged waveform, just I _TIMINGA linear function.V _TONBe connected to the input of comparator 49, in order to the control trip point, at that point, timing voltage V _TIMINGTermination signal TERM is set to logic high, to stop charging current I _CH

It should be noted, by COILON to correction voltage V _ERRAdjust to produce threshold voltage V _TONThe time, I _TIMINGBasically keep constant, thereby make product T _CH* D _CYCLEBasically keep constant.As mentioned above, as product T _CH* D _CYCLEWhen keeping constant, I _COILMean value be SIN function, and with alternating current circuit voltage VAC homophase, thereby obtain high power factor.When going the switching coil electric current I according to constant frequency with clock signal CLOCK _COILThe time, just can obtain high power factor, so that the level of reduction electromagnetic interference or help to make its decay by filtering.

Fig. 5 is a schematic diagram, is illustrated in a current modulator 14 among alternative embodiment.In this embodiment, correction voltage V _ERRDirectly be connected to the inverting input of comparator 49, with control V _TIMINGSwitching threshold, pass through I simultaneously _COILDuty cycle DC to I _TIMINGRegulate, so that make product T _CH* D _CYCLEKeep constant.

Amplifier 60 plays the effect of integrator, its integration time constant T _SW=C ₆₁* R ₆₈, here, C ₆₁Be the capacitance of capacitor 61, R ₆₈It is the resistance value of resistor 68.Preferably select capacitor 61 and resistor 68 like this, make T _SWNumerical value be far longer than cycle of CLOCK.

From T1 to T3, work as I _COILDuring for nonzero value, COILON is in high level, and switch 50 is in open-circuit condition, reference current I _REF1Flow through resistor 66, thereby form voltage V at node 77 places ₆₆=I _REF1* R ₆₆, here, R ₆₆It is the resistance value of resistor 66.From T3 to T4, work as I _COILDuring for null value, COILON is in low level, and switch 50 is in closure state, the voltage V on node 77 ₆₆=0.0V.When CLOCK carries out integration in the cycle, voltage V ₆₆Time weighted average be I _REF1* R ₆₆* D _CYCLE=V ₆₆* D _CYCLE

The base current of the transistor 65 that is connected with resistor 69 is being controlled in the output of amplifier 60.Such configuration produces collector current I ₆₅, from reference current I _REF2In deduct collector current I ₆₅, to produce electric current I _OUT, it produces voltage V on resistor R 67 ₆₇Collector current I ₆₅One feedback paths is provided, and it makes V ₆₆And V ₆₇Keep identical effective average potential, therefore, I _OUT=I _REF1* D _CYCLE* R ₆₆/ R ₆₇Set up regularly electric current I by current mirror 63 _TIMINGMirror image I _OUT, and multiply by factor K, make I _TIMING=K*I _OUT=K*I _REF1* D _CYCLE* R ₆₆/ R ₆₇Therefore, I _TIMINGWith duty cycle D _CYCLEBe directly proportional.

As mentioned above, I _TIMING Capacitor 28 is charged, to produce jagged timing voltage V _TIMING, in comparator 49, this sawtooth voltage is followed V _ERRCompare, to produce control signal TERM.Because at V _INOne-period in, I _TIMINGBasically keep constant, and V _TIMING=I _TIMING* T _CH=K*I _REF1* D _CYCLE* T _CH* R ₆₆/ R ₆₇So, product T _CH* D _CYCLEAlso keep constant basically.Therefore, I _COILThe average current that a sinusoidal shape is arranged, pfc circuit 100 has a high power factor simultaneously.

Generally speaking, the invention provides a kind of pfc circuit, this circuit can move under constant or approaching constant frequency, thus, helps to reduce electromagnetic interference by filtering.Latch has an output, and in response to a hopping edge of clock signal, the actuating coil electric current is to produce the PFC signal.Current-modulation electric circuit inspection PFC signal, setting up the charging interval of coil current, and the magnetic test coil electric current, so that set up the duty cycle of coil current on the one-period of clock signal.The output of current-modulation circuit is applied to the input of latch, and so that a control signal to be provided, the latter is a function of charging interval and duty cycle.

Claims (10)

1. a power factor correction (PFC) circuit comprises:

First latch, it has an output, is used in response to a hopping edge actuating coil electric current of clock signal producing the PFC signal, and an input, be used to receive control signal; And

The current-modulation circuit, it has: a first input end is used to receive the PFC signal, to set up the charging interval of coil current; One second input, it is connected for the magnetic test coil electric current, so that set up the duty cycle of coil current on the one-period of clock signal; And an output, be used to provide control signal as a function of charging interval and duty cycle.

2. pfc circuit according to claim 1, wherein, the current-modulation circuit also comprises one first switch, it is in response to the transducing signal of second input that is applied to the current-modulation circuit, be used for second input of second amplifier is switched to a reference node from the output of second amplifier, to set up duty cycle.

3. pfc circuit according to claim 1 also comprises a current sensor, and it has an input, is connected for the magnetic test coil electric current, and an output, is used to provide transducing signal.

4. pfc circuit according to claim 3, wherein, current sensor comprises:

First amplifier, it has a first input end, is connected to the input of current sensor, and one second input, is used to set up the threshold level of coil current; And

Second latch, it has: a first input end is connected to the output of first latch; One second input is connected to an output of first amplifier; And an output (34), be connected to second input of current-modulation circuit, be used to produce transducing signal, be first logic state corresponding to the hopping edge of clock signal, be second logic state when coil current is reduced to threshold level when following.

5. pfc circuit according to claim 4, wherein, the current-modulation circuit comprises:

A comparator, it has a first input end, is connected for receiving a serrated signal, and an output, is used to provide control signal;

One second amplifier, it has a first input end, is used to receive the PFC signal, and one second input is used to receive reference signal, and an output, is connected to second input of comparator; And

An average circuit, it has an input, is connected to the output of second latch, in order in the cycle of clock signal, first reference current is averaged, to produce the average current of an expression duty cycle.

6. pfc circuit according to claim 5, wherein, average circuit comprises:

A switch is used for switching between first reference signal and transducing signal, to produce a duty cycle signal; And

An integrator, it has a first input end, is used to receive second reference signal, and one second input is used to receive the duty cycle signal, and an output, is used to provide average current.

7. method that is used for correcting power factors comprises following each step:

In the beginning of a clock cycle, the actuating coil electric current is to produce a power factor correction (PFC) signal;

The magnetic test coil electric current is to determine the duty cycle of coil current on this clock cycle; And

Come the live part of terminated line loop current with a control signal, described control signal is a function of PFC signal and duty cycle.

8. according to the described method of claim 7, wherein, stop step and comprise following each step:

Difference between the PFC signal and first reference signal is amplified, to produce a correction signal; And

With correction signal divided by duty cycle, to produce control signal.

9. described according to Claim 8 method, wherein, the multiplication step comprises following each step:

Correction signal is sent to the first input end of an amplifier;

When coil current flows, second input of amplifier is switched to an output of this amplifier; And

When coil current stops, second input of amplifier is switched to a reference node.

10. an integrated power factor correction (PFC) circuit comprises:

A drive circuit, it has a first input end, is used for the receive clock pulse, so that the actuating coil electric current, one second input is used to receive the live part of control signal with the terminated line loop current, and an output, be used for producing a PFC signal with coil current; And

A modulation circuit, it has a first input end, be connected for detecting the PFC signal to set the amplitude of coil current, one second input, be used to monitor coil current in the one-period of clock pulse to produce a duty cycle signal, and an output, being used to provide control signal, it is a function of described amplitude and duty cycle signal.

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