Background technology
During the operation of tradition AC-DC translation circuit, net side power factor generally all is about 0.6 ~ 0.7, and can produce a large amount of harmonic currents, and electrical network is caused serious harm.For satisfying High Power Factor, suppressing the requirement that harmonic wave produces, all will add usually has the PFC of power factor emendation function level.The PFC level is a DC/DC switch converters that is added between rectifier and the load, applied voltage current feedback technology, and the waveform that makes input current reaches the purpose that improves power factor near sinusoidal wave.According to the different requirements of different loads, need between PFC level and load, add the DC/DC level usually with the regulation voltage size to voltage swing.
DCM Boost pfc converter has the advantage that switching tube zero current turning-on and booster diode do not have reverse recovery, and switching frequency is constant.Inductive current changed with input voltage during but this converter switches pipe was opened, mean value is sinusoidal form, but switching tube blocking interval inductive current mean value is the non-sine form, thereby the inductive current mean value in a switch periods also is the non-sine form, its PF value is relatively low, especially when high pressure is imported.
Traditional control method is all being decided duty ratio control, and the control method commonly used that is applied to DCM Boost pfc converter is peak current control, because input current waveform is with U
m/ U
oIncrease and THD is increased, need add harmonic compensation at comparator input terminal.The control method of another novel injection triple-frequency harmonics because the triple-frequency harmonics content that is injected is relevant with input voltage, needs online adjusting to inject harmonic content, and implementation is too complicated.
Tradition realizes that the circuit of control strategy all is relatively to obtain with duty cycle signals and sawtooth signal, when duty ratio expression formula more complicated, then need complex calculation circuit or digital match to simplify and just can obtain, certainly will increase the loading level of analog circuit like this or reduce control precision.
The utility model content
The purpose of this utility model provides a kind of circuit of power factor correction of variable duty cycle control, adopt the momentum area to equate principle, acquisition can realize the variable duty cycle control sequence of High Power Factor, solve conventional P FC control method complexity, problem that precision is not high, when improving power factor, also obtained less output voltage ripple and higher efficient.The utility model is achieved through the following technical solutions:
A kind of circuit of power factor correction of variable duty cycle control, comprise the circuit topological structure of Boost booster converter and the control circuit of realization variable duty cycle sequence, realize that the control circuit of variable duty cycle sequence comprises input voltage detection circuit, output voltage detecting circuit, analog operational circuit and pulse regulation driver; The input voltage sample resistance of described input voltage detection circuit is connected input filter capacitor C
InTwo ends, the input voltage sample resistance of input voltage detection circuit is first sampling point for first resistance and second resistance of series connection between described first resistance and second resistance, first sampling point is connected with an input of subtracter in the analog operational circuit; The output voltage sample resistance of described output voltage detecting circuit is connected between the negative electrode and ground of diode in the circuit topological structure of Boost booster converter, the output voltage sample resistance of output voltage detecting circuit is the 3rd resistance and the 4th resistance of series connection, be second sampling point between described the 3rd resistance and the 4th resistance, another input of subtracter and an input of divider are connected in second sampling point and the analog operational circuit; Described analog operational circuit comprises subtracter, divider, multiplier, sawtooth signal generator and comparator, and wherein, the output of subtracter is connected with another input of divider, and the output of divider is connected with an input of comparator; Sawtooth signal is connected with two inputs of multiplier that (the constant term K of multiplier is to calculate square value

), another input of the output termination comparator of multiplier, the output of comparator is connected with the input that pulse regulation drives.
The circuit topological structure of described Boost booster converter comprises inductance, switching tube and diode, one end of described inductance is connected with the positive output end that single-phase diode is not controlled rectifier bridge, the other end of inductance is connected with the drain electrode of switching tube, the source electrode of switching tube is connected with the negative output terminal that single-phase diode is not controlled rectifier bridge, and the gate pole of switching tube is connected with the pulse-width regulated output end of driver; Simultaneously, the other end of inductance is connected with diode anode, and the negative electrode of diode is connected with the DC/DC level through output inductor.
The control principle of the pfc circuit of above-mentioned high input power factor: the circuit topological structure that adopts the Boost booster converter, equate principle according to the momentum area, control the break-make of electronic power switch with the variable duty cycle control sequence, carry out the high frequency Active Power Factor Correction, the input inductance electric current is equated with the momentum area of half-sinusoid electric current in each switch periods, thereby realize the sineization of input current, make input power factor approach 1.
Described variable duty cycle control sequence equates that according to the momentum area principle draws, and specifically comprise: per half AC side input current cycle is divided into n minor time slice, and the width of each time period is a switch periods
,, make the integral area of inductive current waveform to each switch periods time period
Equal the integral area of standard sine half-wave in this time period
, promptly
, wherein
(2)
Be inductive current peak,
Be the conducting duty ratio of each switch periods under the inductive current discontinuous mode (DCM),
Be inductive current duty ratio fall time in each switch periods under the discontinuous mode,
Be the output voltage that single-phase diode is not controlled rectifier bridge (B),
Be the output voltage of PFC level,
Be the induction reactance value of the middle inductance (L) of circuit topological structure (1) of Boost booster converter,
Be the input voltage peak value,
Be the input voltage angular frequency,
Be desirable input Sinusoidal Input Currents amplitude,
Be the standard sine half-wave at the middle radian value of each switch periods time period,
Be power output, equate by (1), (2) formula
(3) formula be exactly according to momentum equate that principle obtains about duty cycle sequence square expression formula.
Above-mentioned PFC control method can get according to (3) formula conversion
In each switch periods, to time t timing, (4) formula is set up up to a certain moment, at this moment be the moment of on-off switching tube.
Sawtooth signal in the described analog operational circuit is the clock signal of energy cycle zero clearing, and the slope of sawtooth waveforms is numerically equal to
, the cycle is
The circuit topological structure of control circuit of the present utility model and Boost booster converter has constituted the PFC level of LED driving power commonly used jointly, and the prime of PFC level is through input filter capacitor C
InThe output of not controlling rectifier bridge with single-phase diode is connected, and the back level of PFC level is connected with the DC/DC level of LED driving power commonly used with output filter capacitor through output inductor.
Compared with prior art the utlity model has following advantage: solved traditional DCM Boost pfc converter and existed current pulsation big, what power factor was low determines, can in whole input voltage range power factor is increased to and approach 1; Control circuit is realized easily, abandon original compare with the time sawtooth waveforms the method for duty ratio, open electric circuit or match that the involution of application time sawtooth signal replaces originally will using are simplified, make that control circuit is simpler, control strategy is more accurate, only realize, help integrated on a large scale with some basic analog operational circuits; Compare with deciding duty ratio control, can not only make input power factor, can also reduce output voltage ripple, make output voltage approach to stablize near 1.
This control circuit is applied to the PFC level of LED driving power, not only High Power Factor can be realized high efficiency illuminalive power-supply, and output voltage ripple reduce to reduce requirement to the output capacitance capacity, so just can with long ceramic electrical of life-span perhaps thin-film capacitor replace short big electrochemical capacitor of big life-span of volume, the life-span of improving the LED driving power on the whole.
Embodiment
Below be in conjunction with the led drive circuit of PFC level,, the concrete enforcement of technical solutions of the utility model is described in further detail, but enforcement of the present utility model and protection range be not limited thereto as accompanying drawing 1 for band variable duty cycle control.
The basic structure of led drive circuit by the input power supply, do not control rectifier bridge, input filtering, PFC level, output filtering, DC/DC level, LED lamp load various piece and be connected in sequence.
Make input voltage be
, the output voltage through not controlling rectifier bridge is so
In a switch periods, inductive current peak is:
Wherein
Expression switch conduction duty ratio.
In each switch periods, equate by the weber number at inductance two ends:
Wherein
The duty ratio of inductive current fall time in the expression switch periods.
Can get by (6):
According to (5) and (6) Shi Kede
(8)
Input current is so:
Will
Standardization is got base value and is
So,
As seen, the waveform of input current is only relevant with the no-load voltage ratio of Boost converter,
More little, input current waveform is more near SIN function, and the PF value is high more.Otherwise the input voltage amplitude is more near output voltage amplitude, and the PF value is low more, and the amplitude that this has just limited input voltage is unfavorable for the power factor adjusting.
The circuit topological structure 1 of described Boost booster converter comprises inductance L, switching tube Q and diode D, one end of described inductance L is connected with the positive output end that single-phase diode is not controlled rectifier bridge B, the other end of inductance L is connected with the drain electrode of switching tube Q, the source electrode of switching tube Q is connected with the negative output terminal that single-phase diode is not controlled rectifier bridge B, and the gate pole of switching tube Q is connected with the output of pulse-width regulated driver 5; Simultaneously, the other end of inductance L is connected with diode D anode, and the negative electrode of diode D is through output inductor L
oBe connected with the DC/DC level.
Therefore, the utility model proposes a kind of variable duty cycle control method based on the equal principle of momentum area, to realize the high input power factor in the wide input voltage range, specific implementation method is as follows:
Per half AC side input current cycle is divided into n minor time slice, and the width of each time period is a switch periods
,, make the integral area of inductive current waveform to each switch periods time period
Equal the integral area of standard sine half-wave in this time period
, promptly
, wherein
Be inductive current peak,
Be the conducting duty ratio of each switch periods under the inductive current discontinuous mode,
Be inductive current duty ratio fall time in each switch periods under the discontinuous mode,
Be the output voltage that single-phase diode is not controlled rectifier bridge B,
Be the output voltage of PFC level,
Be the induction reactance value of inductance L in the circuit
topological structure 1 of Boost booster converter,
Be the input voltage peak value,
Be the input voltage angular frequency,
Be desirable input Sinusoidal Input Currents amplitude,
Be the standard sine half-wave at the middle radian value of each switch periods time period,
Be power output, equate by (1), (2) formula
(3) formula be exactly according to momentum equate that principle obtains about duty cycle sequence square expression formula.
The control circuit of realizing the variable duty cycle sequence obtains according to (3) formula conversion, promptly
In each switch periods, to time t timing, (4) formula is set up up to a certain moment, at this moment be the moment of on-off switching tube.
Can obtain one about duty ratio by finding the solution
Sequence, make input current waveform in each switch periods for sinusoidal wave, thereby realize PF=1.
By the momentum area equate (3) formula that principle calculates be exactly about duty cycle sequence square expression formula.Traditional control circuit realizes it being the duty cycle circuit of structure (3) expression formula, relatively get duty cycle signals with sawtooth waveforms again, like that can be because expression formula has radical to exist, and make control circuit very complicated, and, can reduce the accuracy of control like that if the cancellation radical just must come match to simplify by Taylor expansion.So the realization of control circuit is by obtaining (4) formula to (3) formula abbreviation in the utility model, utilize (4) formula two ends semaphore relatively obtained required control signal.
As Fig. 1, realize that the control circuit of variable duty cycle sequence comprises input voltage detection circuit 2, output voltage detecting circuit 3, analog operational circuit 4 and pulse regulation driver 5; The input voltage sample resistance of described input voltage detection circuit 2 is connected input filter capacitor C
InTwo ends, the input voltage sample resistance of input voltage detection circuit 2 is first resistance R of series connection
1With second resistance R
2, described first resistance R
1With second resistance R
2Between be the first sampling point a, the first sampling point a is connected with an input of subtracter in the analog operational circuit 4; The output voltage sample resistance of described output voltage detecting circuit 3 is connected between the negative electrode and ground of diode D in the circuit topological structure 1 of Boost booster converter, and the output voltage sample resistance of output voltage detecting circuit 3 is the 3rd resistance R of series connection
3With the 4th resistance R
4, described the 3rd resistance R
3With the 4th resistance R
4Between be the second sampling point b, another input of subtracter and an input of divider are connected in the second sampling point b and the analog operational circuit 4; Described analog operational circuit 4 comprises subtracter, divider, multiplier, sawtooth signal generator and comparator, and wherein, the output of subtracter is connected with another input of divider, and the output of divider is connected with an input of comparator; The sawtooth signal generator is connected with two inputs of multiplier to calculate square value, and the constant term K of multiplier is
Another input of the output termination comparator of multiplier, the output of comparator is connected with the input of pulse regulation driver 5.Sawtooth signal in the analog operational circuit 4 is the clock signal of energy cycle zero clearing, and the clock signal slope is numerically equal to
, the cycle is
, the signal expression that makes the sawtooth signal generator produce is
, and each cycle zero clearing is once.
The circuit topological structure of above-mentioned control circuit and Boost booster converter has constituted the PFC level of LED driving power commonly used jointly, and the prime of PFC level is through input filter capacitor C
InThe output of not controlling rectifier bridge with single-phase diode is connected, and the back level of PFC level is connected with the DC/DC level of LED driving power commonly used with output filter capacitor through output inductor.
This PFC level of variable duty cycle control that can realize is applied in the LED driving power, when the input low-voltage, input current waveform as shown in Figure 2, the current waveform on inductance after the rectification just can find out intuitively that the sineization effect is fine as shown in Figure 3 from waveform.When input during high voltage, input current waveform as shown in Figure 4, comparing with accompanying drawing 2 has a bit little distortion at the current over-zero place, the current waveform on inductance after the rectification as shown in Figure 5, the relative accompanying drawing 3 of its sineization effect has some distortions on sinusoidal wave peak value.From PF value figure low, when high pressure is imported, power factor is all more than 0.99, as accompanying drawing 6 and accompanying drawing 7.Output voltage waveforms when low pressure when input and high pressure input is shown in accompanying drawing 8 and accompanying drawing 9, the output voltage stabilization response speed is fast as can be seen, from output voltage steady-sxtate wave motion figure as can be seen the output ripple value less than 4.5V, and input voltage raises, the increase of output voltage ripple value is not remarkable, as accompanying drawing 10 and accompanying drawing 11.
Through above-mentioned analysis, equate that based on momentum the variable duty cycle control method of principle is applied to the PFC level of LED driving power with this, power factor height not only, and be applicable to wide input voltage, output voltage ripple is little, reduced requirement to the output capacitance capacity, can with long ceramic electrical of life-span perhaps thin-film capacitor replace short big electrochemical capacitor of big life-span of volume, the life-span of improving the LED driving power on the whole.