Embodiment
Fig. 1 is the schematic diagram of discontinuous mode power factor correction according to the preferred embodiment of the invention (PFC) transducer.Power factor correction converter comprises electric bridge 10, inductor 20, rectifier 30 and capacitor 40.For feedback operation, power factor correction converter more comprises controller 100; Capacitor 41 and 43; Resistor 50,51 and 53; The voltage divider that comprises resistor 55 and resistor 56; Transistor 60 and 62 and diode 75.Via power factor correction converter, exchange the input of (AC) line and be converted to direct current (DC) output VO, wherein switch current 91 switchings come control energy via the AC of input inductor 20, rectifier 30 and capacitor 40.The purpose of power factor correction converter is that the electric current I AC Waveform Control with AC line input is a sinusoidal waveform, and it is identical with AC line input voltage VAC to keep the phase place of IAC.Via the rectification of electric bridge 10, VIN with respect to the ground connection of power factor correction converter always for just.
V
IN(t)=V
Psin(ωt)
Wherein
(in root mean square " RMS " value) input current can be expressed as similarly:
I
IN(t)=I
Psin(ωt);
Wherein
Then the input power of power factor correction converter can be given as:
P
IN=V
P×I
P/2
(η) introduces described equation with efficient, and power output is given as:
P
O=P
IN×η
P
O=V
P×I
P×η/2----------------------------------(1)
Equation 1 can be expressed as relevant with input current
I
P=(2×P
O)/(V
P×η)---------------------------------(2)
When the conduction mode of border, the peak value switch current (IL-P) of inductor 20 just in time is the twice of average inductor current.
I
L-P=2×I
P
I
L-P=(4×P
O)/(V
P×η)------------------------------(3)
Switch current 91 deformation type is at that time showed.
I
L(t)=(4×P
O)sin(ωt)/(V
P×η)----------------------------(4)
Switch current 91 also can solve inductor L is charged to peak current required turn-on time, for example I=L (di/dt).
T
ON=I
L-P×L/V
P
T
ON=(4×P
O×L)/(V
P 2×η)?----------------------------------(5)
T
OFF=(I
L-P×L)/(V
O-V
P)
T
OFF=(4×P
O×L)/[(η×V
P)×(V
O-V
P)]?-------------------(6)
T=T
ON+T
OFF
Equation 5 can be expressed as relevant with power output.
P
O=[V
P 2×η/(4×L)]×T
ON -------------------(7)
According to the equation 7 of front, it should be noted that power output is by TON control turn-on time.By limiting maximum turn-on time, peak power output will be restricted, especially for low-voltage variation, and the situation of brownout (brownout) for example.
When AC power was applied to power factor correction converter, the dc voltage on the output voltage VO produced via electric bridge 10, inductor 20, rectifier 30 and capacitor 40.By the parasitic diode 32 of feedback resistor 55 and controller 100, output voltage VO is charged to capacitor 41.Voltage VCC among the power supply terminal VCC of controller 100 (hereinafter being expressed as " VCC ") is the voltage level of capacitor 41.In case the voltage VCC in the capacitor 41 is higher than the actuation threshold threshold voltage of controller 100, controller 100 will be activated.In the moment that controller 100 starts, can connect transistor 62 at for example 2 volts the voltage that the reference terminal RT of controller 100 (hereinafter being expressed as " RT ") locates to set up.Simultaneously, resistor 56 ground connection.Resistor 55 and 56 forms the voltage divider of feedback loop.Therefore, resistance 55 and 56 combined resistance are connected to the back coupling terminal FB (hereinafter being expressed as " FB ") of controller 100.
FB and compensation terminal COM (hereinafter being expressed as " COM ") serve as the input terminal and the lead-out terminal of error amplifier 205, as shown in Figure 3 and as will be described in more detail below.Be connected capacitor 43 between FB and the COM in order to frequency compensation as the low frequency bandwidth below the line incoming frequency.The OUT lead-out terminal of controller 100 (hereinafter being expressed as " OUT ") output switching signal is with driving transistors 60.After controller 100 started, the additional winding of inductor 20 charged via the 75 pairs of capacitors 41 of diode that are arranged between power supply terminal VCC and the detecting terminal DET, and was controller 100 power supplies.Voltage in the capacitor 41 remains on and is higher than outage threshold voltage to keep operation and to prevent that voltage VCC is in low level in controller 100.
When the signal of the OUT of transistor 60 origin self-controllers 100 drives when connecting, inductor 20 is recharged via transistor 60.Resistor 53 sensing switch currents 91 and be connected to the input terminal VS (hereinafter being expressed as " VS ") of controller 100.As long as the voltage level at VS place is higher than deboost VR3, will cut off from the signal of OUT, this has realized that Cycle by Cycle (cycle-by-cycle) electric current that is used to switch limits.When transistor 60 was disconnected by the signal from OUT, the energy that is stored in the inductor 20 was discharged into output voltage VO by discharging current 92 via rectifier 30.Illustrate waveform among Fig. 2.In a single day discharging current 92 drops to zero, will detect no-voltage in the additional winding of inductor 20.The detecting terminal DET (hereinafter being expressed as " DET ") of controller 100 is connected to additional winding via resistor 51, is used to detect zero current condition.In case detect zero current condition, the shut-in time postpones td and just begins.After the shut-in time postponed td, controller 100 just can begin next switching cycle.The reference terminal RT of slave controller 1070 is connected to the maximum turn-on time of the resistor 50 decision switching signals signal of lead-out terminal (for example from) on ground (GND).
Referring to Fig. 3,4 and 5, it is the schematic diagram of preferred embodiment that is used for the control circuit 100 of the discontinuous mode power factor correction converter of the present invention shown in Fig. 1.Referring to Fig. 3, at first, control circuit 100 comprises a constant current source 315; Delayed current source 300; Error amplifier 205; Comparator 210,211,214 and 215; Inverter 221,222 and buffer 226; NAND gate 223,225; NOR gate 227 and set-reset flip-floop 228.Apply the voltage level in the detecting terminal that the electric current I R1 that is produced by constant current source 315 draws high controller 100.In case the voltage level of DET is detected as low signal, promptly the voltage level of DET is lower than first threshold voltage VR1, and comparator 210 is with the logic low state output signal so, and then via disconnecting transistor 231 with non-223 output.Then open the shut-in time delay td shown in beginning Fig. 2 by cutting off transistor 231.The electric current I d that is produced by delayed current source 300 begins capacitor 241 is charged, in case and the voltage level of capacitor 241 be higher than the second threshold voltage VR2, comparator 211 will be with the logic high state output signal.Via using set-reset flip-floop 228, decide switching signal PWM.The shut-in time delay can be set fourth as:
T
d=(C
241×V
R2)/I
d?----------------------(8)
Wherein C241 is the electric capacity of capacitor 241.
Shut-in time postpones the function that td is modulated into feedback voltage and VCC voltage.Respectively with the output of comparator 211 with come the feedback voltage of self-feedback terminal to be applied to two inputs of set-reset flip-floop 228.To be applied to the input terminal of error amplifier 205 from the feedback voltage of FB, and reference voltage VR will be applied to another input terminal of error amplifier 205, and then produce once the voltage VCOM that amplifies from error amplifier 205.Then voltage VCOM is applied to the positive input terminal of comparator 214, and signal SAW is applied to negative input end of comparator 214.Then the output of comparator 214 is applied to an input terminal of NAND gate 223 and an input terminal of NAND gate 225.Another input terminal of NAND gate 225 is applied in the PULSE signal.To describe signal SAW and PULSE in detail after a while.Then the output of NAND gate 225 is applied to an input terminal of NOR gate 227.Another input terminal of NOR gate 227 is applied in the output of inverter 222.The output of inverter 222 is from the anti-phase signal of the output of comparator 215.As shown in fig. 1, comparator 215 input terminal is applied in the voltage of the current-sense terminal of self-controller 100.Another input terminal of comparator 215 is applied in the 3rd threshold voltage VR3.Via the voltage level, signal SAW and the PULSE that adjust VCOM, the shut-in time postpones to be modulated into by set-reset flip-floop 228 function of feedback voltage.
Referring to Fig. 3, can produce according to loading condition from the electric current I d in delayed current source 300.Circuit among Fig. 5 comprises first current mirror of being made up of transistor 273,274 and 275; Second current mirror of forming by transistor 277 and 278; And the 3rd current mirror of forming by transistor 291 and 292.The image current that transistor 270 and resistor 50 produce in first current mirror.The gate terminal of transistor 270 is couple to the output of operational amplifier (op-amplifier) 260.The positive input terminal of operational amplifier 260 is applied in the 7th threshold voltage VR7, and negative input end of operational amplifier 260 is couple to the source terminal and the resistor 50 of transistor 270.The image current of first current mirror is VR7/R50, thereby and two electric current I T1 and IT2 respectively according to the width/height of transistor 273 relative transistors 274 and 275 than generation.Therefore, electric current I T1 equals (VR7/R50) (N274/N273), and wherein N274, N273 are respectively the width/height ratio of transistor 274 and 273.Electric current I T2 equals (VR7/R50) (N275/N273), and wherein N275, N273 are respectively the width/height ratio of transistor 275 and 273.
Image current in second current mirror is produced by transistor 271 and resistor 282.The gate terminal of transistor 271 is couple to the output of operational amplifier 261.The positive input terminal of operational amplifier 261 is applied in VCOM, and as shown in Figure 3, and negative input end of operational amplifier 261 is couple to the source terminal of transistor 271 and a terminal of resistor 282.The another terminal of resistor 282 is couple to the lead-out terminal and negative input end of operational amplifier 262.The positive input terminal of operational amplifier 262 is applied in the 5th threshold voltage VR5.The image current of second current mirror can be expressed as (VCOM-VR5)/R282, and wherein R282 is the resistance of resistor 282.
Image current in the 3rd current mirror is produced by transistor 293 and resistor 288.The gate terminal of transistor 293 is couple to the output of operational amplifier 264.The positive input terminal of operational amplifier 264 is applied in the 6th threshold voltage VR6, and negative input end of operational amplifier 264 is couple to the source terminal of transistor 293 and a terminal of resistor 288.The another terminal of resistor 288 is couple to the lead-out terminal and negative input end of operational amplifier 265.The positive input terminal of operational amplifier 265 is applied in from by the voltage that produces behind the VCC of resistor 285 and 286 decay.The image current of the 3rd current mirror can be expressed as (VR6-α VCC)/R288, and wherein R288 is the resistance of resistor 288, α=R286/ (R286+R285), and R286 and R285 are respectively the resistance of resistor 286 and 285.
As shown in Figure 3, can obtain the electric current I d in delayed current source 300 via the right side mapping current Ib that adds up the left side mapping electric current I a that produces from image current and produce from image current by the 3rd electric current of transistor 291 mirror images of comparing with transistor 292 by second electric current of transistor 278 mirror images of comparing with transistor 277.The 5th threshold voltage VR5 is the constant that defines the underload level.The 6th threshold voltage VR6 is the low level deboost that is used to define VCC voltage.In case the voltage VCOM that reduces is lower than the 5th threshold voltage VR5, the shut-in time delay will correspondingly increase.When the VCC voltage of decay is lower than the 6th threshold voltage VR6, can reduces the reduction of shut-in time delay, thereby avoid low VCC voltage with the inhibition switching frequency.Switching frequency reduces according to the minimizing of load.Therefore, handoff loss and power consumption under underload and the no-load condition have been reduced.Formula is described below:
I
d=I
a+I
b
I
d=[(V
COM-V
R5/R
282]×K
1+[(V
R6-αV
CC)/R
288]×K
2--------(9)
α=R
286/(R
286+R
285)
K
1=N
278/N
277;
K
2=N
291/N
292;
I
d≤I
T2
I wherein
T2=(V
R7/ R
50) * (N
275/ N
273)
I
T1=(V
R7/R
50)×(N
274/N
273)----------------------------(10)
Referring to Fig. 4, it illustrates the circuit of the preferred embodiment of signal SAW shown in Fig. 3 and PULSE.Described circuit comprises comparator 217, NAND gate 250, transistor 232, current source 310, capacitor 242 and set-reset flip-floop 229.Illustrate the electric current I T1 of current source 310 among Fig. 5.Switching signal PWM is applied to an input terminal of NAND gate 250.The lead-out terminal of NAND gate 250 is applied to the gate terminal of transistor 232.In case switching signal PWM is high, transistor 232 promptly is disconnected.The electric current I T1 of current source 310 begins capacitor 242 is charged and produce the SAW signal of sawtooth waveform in capacitor 242.The switching signal PWM that closes will connect transistor 232, and then capacitor 242 be discharged.The SAW signal is applied to negative input end of comparator 217, and the 4th threshold voltage VR4 is applied to the positive input terminal of comparator 217, and be the PULSE signal on the lead-out terminal of comparator 217 then, it is applied to set-reset flip-floop 229.The output of set-reset flip-floop 229 is applied to another input terminal of NAND gate 250.As shown in Figure 3, if the output voltage V COM of error amplifier 205 is lower than the SAW voltage of signals, or being higher than the 3rd threshold voltage VR3 from the voltage of current-sense terminal, it can close switching signal PWM so for the overcurrent threshold voltage under the overcurrent condition.If it is high that switching signal PWM keeps, as long as SAW voltage of signals level is higher than the 4th threshold voltage VR4, the sawtooth waveform of SAW signal will be discharged so.
Therefore, the maximum turn-on time of switching signal PWM is by (C242 * VR4)/IT1 decides, and wherein C242 is the electric capacity of capacitor 242.As seen, IT1 equals (VR7/R50) * (N274/N273) from equation 10, and equal the maximum turn-on time of switching signal PWM (R50 * C242 * VR4)/[VR7 * (N274/N273)].
Therefore, as shown in fig. 1, decide according to resistor 50 the maximum turn-on time of switching signal PWM.The description of front can be expressed as:
T
ON-MAX=(C
242×V
R4)/I
T1 --------------------(11)
T
ON-MAX=(R
50×C
242×V
R4)/[V
R7×(N
274/N
273)]?----------(12)
Wherein TON-MAX is the maximum turn-on time of switching signal PWM.
Because the maximum turn-on time of switching signal PWM is limited, damage with the overstress of avoiding under the low-voltage condition so the switching device shifter of power factor correction converter is protected.
According to ZCS of the present invention and discontinuous mode power factor correction conversion, next switching cycle starts from the boundary of zero inductance device current status, and wherein shut-in time delay td is almost nil.Energy is given as:
ε=L×I
2/2 -------------------(13)
Power by the power factor correcting step-up converter supplies can be expressed as:
P
O=[V
P 2×η×T
ON 2/(4×L×T)] ---------------(14)
Show T=TON+TOFF in the equation 5 and 6.When loading on of power factor correction converter reduced under the light-load conditions, the shut-in time postponed the corresponding increase of td, and before being inserted in next switching cycle and beginning.Therefore, the switching cycle T of switching signal is extended for:
T=T
ON+T
OFF+t
d ----------------------(15)
Therefore, under underload and no-load condition, the switching frequency of switching signal reduces.Therefore, standby power reduces.In addition, the feature that the shut-in time postpones helps to keep the regulated output voltage VO (VO=PO/IO) of power factor emendation function and holding power factor correcting transducer under light-load conditions.Referring to equation 14,, should produce very little TON pulse duration for extremely light loading condition.Extremely Duan TON has increased the difficulty of power factor correction converter design.The restriction of the short pulse width of TON has been limited the performance of power converter, therefore, must add dummy load at the output of power factor correction converter, to obtain stable output voltage VO.According to equation 14 and 15, it shows that the insertion of shut-in time delay td of the present invention has prolonged switching cycle T and do not needed extremely short TON.Keep stable output voltage VO and do not need dummy load, this has saved the power consumption in the power factor correction converter.
Be understood by those skilled in the art that,, can make various modifications and change structure of the present invention under the situation of scope of the present invention or spirit.In view of aforementioned content,, modification of the present invention and change contain these modifications and change if in the scope of claims and its equivalent, then wishing the present invention.