JP2001103762A - Power factor improving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power factor improving circuit for a switching power supply unit capable of increasing the response speed of an error amplifier, and improving the power factor thereof. SOLUTION: This power factor improving circuit for switching power supply unit including a rectifying circuit REC for rectifying AC voltage, a switching transistor Q1, a filtering output capacitor C3 for applying rectified and filtered voltage to a load RL, an error amplifier including an operational amplifier OA1, and a control circuit such as a pulse width control circuit PWM for controlling the ON period of the switching transistor Q1, is provided with a resistor R0 for detecting current running through the filtering output capacitor C3 and the load RL, and a current feedback circuit FBK for feeding back the AC component of the detected value by the resistor R0, that is, a signal for compensating the low level of ripple voltage to the error amplifier.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply for stabilizing a DC output voltage applied to a load by rectifying and switching an AC voltage by a rectifier circuit and controlling an ON period of the switching. The present invention relates to a power factor correction circuit.

[0002]

2. Description of the Related Art FIG. 10 is an explanatory view of a conventional example, showing a power factor improving circuit of a conventional example applied to a buck converter.
1, L2 is a choke coil, C1 to C3, C are capacitors, Ra to Rd are resistors, D1 is a diode, REC is a rectifier circuit, Q1 is a switching transistor, OA1 is an operational amplifier, STG is a sawtooth wave generator, PWM. Indicates a pulse width control circuit, and RL indicates a load. Iac is an AC current from an AC power supply, Id is a pulsed DC current, Vin is a rectified output voltage, Vd is a DC output voltage applied to the load RL,
Vr indicates a reference voltage.

[0003] The AC power supply is, for example, 100V or 20V.
In general, a 50 V or 60 Hz commercial power supply of 0 V is applied. An AC voltage is applied to a rectifier circuit REC through an input filter including a choke coil L1 and a capacitor C1, and full-wave rectification is performed by the rectifier circuit REC. The signal is turned on and off by the switching transistor Q1, and is input to a smoothing circuit including the choke coil L2, the capacitors C2 and C3, and the diode D1. The capacitor C2 is
The capacitor C3 is a capacitor having improved characteristics with respect to harmonics caused by switching, and the capacitor C3 is a rectifying output capacitor for increasing the capacitance to stabilize the DC output voltage Vd.

A dc output voltage Vd of the terminal voltage of the rectified output capacitor C3 is applied to a load RL, and a resistor R
The DC output voltage Vd is detected by dividing the voltage by a and Rb, and compared with the reference voltage Vr by the operational amplifier OA1. This operational amplifier OA1 forms an error amplifier by a feedback circuit of resistors Rc and Rd and a capacitor C. The operational amplifier OA1 converts an error between the DC output voltage Vd and a set value corresponding to the reference voltage Vr into a pulse width control circuit PWM. To enter.

[0005] The pulse width control circuit PWM is configured to output the output signal of the error amplifier and the signal of several tens of kilograms from the sawtooth wave generator STG.
When the terminal voltage of the capacitor C3 applied to the load RL, that is, the DC output voltage Vd increases, the pulse of the pulse signal according to the frequency of the saw-tooth wave signal is compared with the saw-tooth wave signal having a frequency of several Hz to several hundred kHz. Make it narrower, and conversely,
When the DC output voltage Vd decreases, the pulse width is increased,
According to this pulse width, the switching transistor Q1
Is controlled so that the DC output voltage Vd applied to the load RL becomes a set value.

In this case, the response speed of the error amplifier corresponds to the value of the resistor Rd and the value of the capacitor C. Normally, the response speed is reduced to reduce the slight output voltage (voltage applied to the load RL). Pulse width control circuit PWM due to fluctuation
In general, the pulse width from the pulse is constant.

FIG. 11 is a diagram for explaining the operation of the conventional example.
(A) shows the outline of the waveform of the rectified output voltage Vin, the DC output voltage Vd, and the ripple voltage Vrp, and (B) shows the current Id flowing through the switching transistor Q1 in an ideal state and the current flowing from the AC power supply. An outline of the AC current Iac is shown.

Usually, the response speed of the error amplifier is reduced so as not to respond to the ripple voltage Vrp.
Therefore, when the DC output voltage Vd is constant, the pulse width control circuit PWM applies an ON signal having a constant pulse width to the switching transistor Q1, and the current Id
Are the levels corresponding to the rectified output voltage Vin and have the same pulse width. That is, t1 = t2. Therefore, the AC current Iac from the AC power supply corresponds to the average value of the current Id, almost coincides with the phase of the rectified output voltage Vin, and has a waveform close to a sine wave, as shown by the dotted line. That is, the power factor can be improved.

FIG. 11C shows that the response speed of the error amplifier is increased in order to stabilize the DC output voltage Vd even when the load RL changes suddenly.
And an AC current Iac. That is, it responds to the ripple voltage Vrp shown in (A). When the ripple voltage Vrp becomes a level equal to or lower than the set value of the DC output voltage Vd, the pulse width control circuit PWM responds to the output signal of the error amplifier. On the other hand, when the on-period of the switching transistor Q1 is widened like the pulse width t1, when the ripple voltage Vrp exceeds the set value, the pulse width control circuit PWM switches the switching transistor in response to the output signal of the error amplifier. The ON period of Q1 has a pulse width t
It will be as narrow as 2. Thereby, when the level of the ripple voltage Vrp is low and the level of the rectified output voltage Vin is high, the pulse width becomes wide and the large current I
Since d flows, the AC current Iac shows a peak waveform, which is different from a sine waveform.

[0010]

As described above, the load R
In order to stabilize the load RL by stabilizing the DC output voltage Vd even with a rapid change in L, the capacitance of the capacitors C2 and C3 may be increased to absorb the change, or the error amplifier may be used. It is necessary to increase the response speed to follow the fluctuation. Increasing the capacity of the capacitor has problems in cost and space. When the response speed of the error amplifier is increased, the pulse width control circuit PWM is controlled in response to the ripple voltage Vrp. This ripple voltage Vrp deteriorates the power factor by being delayed by π / 2 from the current flowing through the capacitor.

That is, as shown in FIG. 11C, when the rectified output voltage Vin and the ripple voltage Vrp have different phases and the rectified output voltage Vin is high,
When the ripple voltage Vrp becomes a low level, the high-speed response error amplifier applies an error output signal similar to the decrease in the DC output voltage Vin to the pulse width control circuit PWM. The current Id flows. As a result, the AC current Iac from the AC power supply has a waveform having a peak significantly different from a sine wave, and there is a problem that the power factor deteriorates. SUMMARY OF THE INVENTION It is an object of the present invention to stabilize an output voltage in response to a change in load at a high speed and to improve a power factor.

[0012]

The power factor improving circuit according to the present invention comprises: (1) a switching transistor Q for turning on and off a rectified output voltage of a rectifying circuit REC for rectifying an AC voltage.
1, a smoothing output capacitor C3 for applying to the load RL a DC output voltage Vd that increases as the ON period of the switching transistor Q1 increases, and an error amplifier for detecting an error between the DC output voltage and a set value. And a control circuit for controlling the ON period of the switching transistor Q1 in accordance with the error from the error amplifier, and detects a current flowing through the smoothing output capacitor C3. Then, a current feedback circuit FBK for feeding back to the error amplifier is provided so as to compensate for the low level of the ripple voltage included in the DC output voltage Vd.

(2) The current feedback circuit FEK comprises an operational amplifier OA2 for inputting a voltage across a resistor R0 for detecting a current flowing through a smoothing output capacitor C3 and a load RL;
The output signal of the operational amplifier OA2 is superimposed on a part of the DC output voltage input to the error amplifier via the capacitor C5.

[0014]

FIG. 1 is an explanatory view of an embodiment of the present invention. L1 and L2 are choke coils, C1 to C5 are capacitors, R0 to R9 are resistors, D1 is a diode, Q
1 is a switching transistor, OA1 and OA2 are operational amplifiers, REC is a rectifier circuit, RL is a load, PWM is a pulse width control circuit, STG is a sawtooth wave generator, and FBK is a current feedback circuit. Iac is an AC current from an AC power supply, Id is a pulsed DC current, Vin is a rectified output voltage, Vd is a DC output voltage applied to the load RL, and Vr is a reference voltage.

This embodiment shows a case in which the present invention is applied to a buck converter, and an operational amplifier OA1 and a resistor R are provided so that the output voltage can be stabilized in response to a change in load at a high speed.
4, R5 and the capacitor C4 to increase the response speed of the error amplifier, and provide a smoothing output capacitor C3 and a load R
A current feedback circuit FBK for detecting a current flowing through L and a resistor R0 and feeding back to the error amplifier is provided to improve the power factor.

This current feedback circuit FBK includes resistors R6 to R6.
9, a capacitor C5 and an operational amplifier OA2. The voltage across the resistor R0 is input to the negative terminal and the positive terminal of the operational amplifier OA2 via the resistors R6 and R7, respectively. Compatible operational amplifier OA2
Is applied to the connection point between the resistors R2 and R3 via the resistor R9 and the capacitor C5.

The current flowing through the resistor R0 includes the current flowing through the load RL and the current flowing through the rectifying output capacitor C3. The current flowing through the load RL is normally constant, but flows through the rectifying and smoothing capacitor C3. The current changes. Accordingly, the output signal of the operational amplifier OA2 indicates the sum of the current flowing through the load RL and the current flowing through the smoothing output capacitor C3. However, since the DC component is cut by the capacitor C5, the smoothing is eventually performed. This means that the current flowing through the output capacitor C3 is detected and is fed back to the connection point between the resistors R2 and R3.

The resistors R2 and R3 are for detecting the DC output voltage Vd together with the resistor R1.
2 is input as a detection point of the DC output voltage Vd to the-terminal of the operational amplifier OA1, the reference voltage Vr is input to the + terminal, and a difference signal with respect to the reference voltage Vr is input to the pulse width control circuit PWM. . This pulse width control circuit PWM
Is a control circuit for controlling the on-period of the switching transistor Q1. As in the conventional example, the control circuit compares the sawtooth signal from the sawtooth generator STG with the output signal of the error amplifier. A signal having a pulse width for controlling the ON period of the transistor Q1 is output.

DC output voltage Vd input to the error amplifier
The detection value of the current flowing through the smoothing output capacitor C3 from the current feedback circuit FBK is superimposed on the detection value of
This detected current value is superimposed on the detected voltage value so as to compensate for the low level state of the ripple voltage Vrp. Therefore,
When the ripple voltage Vrp is at a low level and the DC output voltage V
As the d decreases and follows it, the switching
When trying to lengthen the on-period of the transistor Q1, compensation is made by the current detection value so that the ripple voltage Vrp is not low, so that the on / off control of the switching transistor Q1 can be controlled without being affected by the ripple voltage Vrp. can do. Thereby, it is possible to avoid the peak of the AC current Iac and improve the power factor. In this case, by selecting the resistors R2 and R3, it is possible to set the amount of feedback of the detected value of the current flowing through the smoothing output capacitor C3.

FIG. 2 is a diagram for explaining the operation of the embodiment of the present invention. FIG. 2A shows a rectified output voltage V similar to FIG.
In, DC output voltage Vd, and ripple voltage Vrp are shown as outline waveforms, and further, feedback voltage Vfd by current feedback circuit FBK is shown by a dotted line. That is, the current feedback circuit FBK is added to the ripple voltage Vrp detected by the resistors R1 to R3.
And a feedback voltage Vfd corresponding to a current flowing through the capacitor C3 for smoothing output from the inverter. 11B shows the outline of the current Id and the alternating current Iac substantially similar to those shown in FIG. 11B.

As shown in FIG. 2A, when the ripple voltage Vrp goes low, the feedback voltage Vfd of the current feedback circuit FBK is superimposed on the ripple voltage Vrp. A signal that determines that the ripple voltage Vrp is not at a low level is supplied to a pulse width control circuit PWM.
Will be entered. Thereby, the DC output voltage V
Since the pulse width is controlled to be substantially constant without increasing the on-period of the switching transistor Q1 with respect to the ripple voltage Vrp when d is constant, a current Id as shown in FIG. 2B flows. Thereby, the AC current Iac from the AC power supply has a substantially sinusoidal waveform as shown by the dotted line.

The DC output voltage Vd due to a sudden change in the load RL
Is detected by an error amplifier having a fast response speed, and the pulse width control circuit PW
Since M controls the ON period of the switching transistor Q1, the DC output voltage Vd can be stabilized. That is, the response speed of the error amplifier is increased, and the load RL is increased.
Of the DC output voltage Vd caused by the fluctuation of the power supply voltage, and stabilization can be achieved, and the power factor can be improved.

FIG. 3 is an explanatory diagram of a power factor improvement circuit applied to the boost converter. The connection configuration is different from that of FIG.
The same reference numerals indicate the same parts. In this boost converter, the switching transistor Q1 is turned on, a current flows through the choke coil L2, and energy is stored. When the switching transistor Q1 is turned off, the diode stores the energy by the energy stored in the choke coil L2. A charging current flows through the capacitors C2 and C3 via D1, and the terminal voltage of the smoothing output capacitor C3 is applied to the load RL as the DC output voltage Vd.

The difference between the DC output voltage Vd and the set value is obtained by an error amplifier including an operational amplifier OA1 to control a pulse width control circuit PWM.
The on-period of the switching transistor Q1 is controlled by the WM to stabilize the DC output voltage Vd. Further, the response speed of the error amplifier is increased to respond to the ripple voltage. The feedback circuit FBK is provided to feed back a feedback voltage based on a current component flowing through the smoothing output capacitor C3 to the error amplifier, thereby avoiding an increase in pulse width when the ripple voltage is at a low level. Thereby, the power factor is improved by making the waveform of the AC current from the AC power supply a substantially sinusoidal waveform.

FIG. 4 is an explanatory diagram of a power factor improving circuit applied to a buck-boost converter. The connection structure is different from that of FIG. 1, but the same reference numerals denote the same parts. In this buck-boost converter, turning on the switching transistor Q1 causes a current to flow through the choke coil L2 to accumulate energy, and the switching transistor Q1 is turned on.
Is turned off, the charging current flows to the capacitors C and C3 via the diode D1 by the energy accumulated in the choke coil L2, and the terminal voltage of the smoothing output capacitor C3 is applied to the load RL as the DC output voltage Vd. Apply.

The buck-boost converter differs from the boost converter of FIG. 3 in that the polarity of the DC output voltage Vd is inverted, and the difference between the DC output voltage Vd and the set value is determined by the operational amplifier OA1. The pulse width control circuit PWM is controlled by an error amplifier including the switching transistor Q.
1 controls the ON period, stabilizes the DC output voltage Vd, and responds to the ripple voltage by increasing the response speed of the error amplifier. However, the current detection signal detected by the resistor R0 is input. A current feedback circuit FBK is provided to feed back a feedback voltage based on a current component flowing through the smoothing output capacitor C3 to the error amplifier, thereby avoiding an increase in pulse width when the ripple voltage is at a low level. Thereby, the power factor is improved by making the waveform of the AC current from the AC power supply a substantially sinusoidal waveform.

The configuration shown in FIGS. 1, 3 and 4 is as follows.
A case is shown in which a rectifier circuit REC is directly connected to an AC power supply to perform full-wave rectification.
It is also possible to adopt a configuration in which a desired voltage is rectified by the rectifier circuit REC.

FIG. 5 is an explanatory diagram of a power factor improving circuit applied to the forward converter. The same reference numerals are given to portions having the same functions as those of FIG.
1, D2 indicates a diode. AC voltage rectifier circuit RE
The rectified output voltage rectified by C is turned on and off by the switching transistor Q1 and applied to the primary winding of the transformer T1, and the induced voltage of the secondary winding corresponding to the current flowing through this primary winding is expressed by a diode D1, A rectifying and smoothing circuit composed of D2, a choke coil L2 and capacitors C2 and C3 performs rectification and smoothing to obtain a DC output voltage, and a load RL
Is applied.

The difference between the DC output voltage and the set value is obtained by an error amplifier including an operational amplifier OA1 to control the pulse width control circuit PWM.
Controls the ON period of the switching transistor Q1 to stabilize the DC output voltage.
As in the case described above, the response speed of the error amplifier is increased to respond to the ripple voltage. However, a current feedback circuit FBK is provided, and the smoothing output capacitor C3 is provided.
By feeding back a feedback voltage based on the current component flowing to the error amplifier to the error amplifier, it is possible to avoid an increase in pulse width when the ripple voltage is at a low level. Thereby, the power factor is improved by making the waveform of the AC current from the AC power supply a substantially sinusoidal waveform.

FIG. 6 is an explanatory diagram of a power factor improving circuit applied to a flyback converter. In FIG. 6, the same functional portions as those in FIG.
The rectified output voltage rectified by the EC is turned on and off by the switching transistor Q1 and applied to the primary winding of the transformer T1, and the voltage induced in the secondary winding when the switching transistor Q1 is off is rectified by the diode D1. , And the terminal voltage thereof is applied to the load RL as a DC output voltage.

The difference between the DC output voltage and the set value is obtained by an error amplifier including an operational amplifier OA1 to control a pulse width control circuit PWM.
Controls the on-period of the switching transistor Q1 to stabilize the DC output voltage applied to the load RL. Further, as in the above-described case, the response speed of the error amplifier is increased to reduce the ripple voltage. A current feedback circuit FBK is provided, and a feedback voltage based on a current component flowing through the smoothing output capacitor C3 is fed back to the error amplifier, so that the pulse when the ripple voltage is at a low level is provided. Avoid widening. Thereby, the power factor is improved by making the waveform of the AC current from the AC power supply a substantially sinusoidal waveform.

FIG. 7 is an explanatory diagram of a power factor correction circuit applied to a bridge converter. The same functional portions as in FIGS. 5 and 6 are denoted by the same reference numerals, and T2 denotes a transformer, Q1 to Q1.
Q4 is a switching transistor, C6 is a capacitor, D3 and D4 are diodes, and DV is a frequency divider.

The rectified output voltage of the rectifier circuit REC is applied to the primary winding of the transformer T2 via the capacitor C6 with the switching transistors Q1 and Q4 turned on, and then the switching transistors Q2 and Q3 are turned on and turned on. A reverse rectified output voltage is applied to the primary winding of T2 via a capacitor C6, and the induced voltage of the secondary winding having a center tap is rectified by diodes D3 and D4, and the choke coil L2 and capacitors C2 and C3 are rectified. To make a DC output voltage, and this DC output voltage is applied to the load RL.

The difference between the DC output voltage and the set value is obtained by an error amplifier including an operational amplifier OA1 to control the pulse width control circuit PWM.
Controls the on-period of the switching transistors Q1 to Q4 by a signal divided by a frequency dividing circuit DV and applied to the gates of the switching transistors Q1 and Q4, and the switching transistors Q2 and Q3.
And the phase difference between the signal applied to the gate of the switching transistor Q1 and the switching transistor Q1,
Q4 and the switching transistors Q2 and Q3 are turned on alternately according to the pulse width control according to the period of the sawtooth wave.

The terminal voltage of the smoothing output capacitor C3 is applied to the load RL as a DC output voltage, and the resistance R
1, R2, and R3, the DC output voltage is detected, and the reference voltage Vr is compared with the operational amplifier OA1 to input an error to the pulse width control circuit PWM. Pulse width control for determining the ON period of Q4 is performed. Further, as in the case described above, the response speed of the error amplifier is increased to respond to the ripple voltage.
Is provided to feed back a feedback voltage based on a current component flowing through the smoothing output capacitor C3 to the error amplifier, thereby avoiding an increase in pulse width when the ripple voltage is at a low level. Thereby, the power factor is improved by making the waveform of the AC current from the AC power supply a substantially sinusoidal waveform.

FIG. 8 is an explanatory diagram of a power factor improving circuit applied to a half-bridge converter. The same functional portions as in FIG. 7 are denoted by the same reference numerals, and C7 and C8 are capacitors. When the switching transistor Q1 is turned on,
The rectified output voltage of the rectifier circuit REC is applied to the primary winding of the transformer T2 via the capacitor C8.
7 discharges through the primary winding. When the switching transistor Q2 is turned on in the next cycle, the rectified output voltage of the rectifier circuit REC is applied to the primary winding of the transformer T2 via the capacitor C7.
8 discharges through the primary winding. Therefore, a current in the opposite direction alternately flows through the primary winding of the transformer T2. In this half-bridge converter, for example, the number of switching transistors can be halved compared to the bridge converter of FIG.

Then, the induced voltage of the secondary winding having the center tap of the transformer T2 is rectified by the diodes D3 and D4 and smoothed by the choke coil L2 and the capacitors C2 and C3 to obtain a DC output voltage. A voltage is applied to the load RL. Further, the error between the DC output voltage and the set value is obtained by the error amplifier and input to the pulse width control circuit PWM. The frequency is divided by 2 by the frequency dividing circuit DV to alternately control the switching transistors Q1 and Q2. A current feedback circuit FBK is provided to avoid an increase in pulse width when the ripple voltage is at a low level due to a response to a ripple voltage caused by increasing a response speed of the error amplifier. The feedback voltage based on the current component flowing through the smoothing output capacitor C3 is fed back to the error amplifier, thereby compensating for a period in which the ripple voltage is at a low level.

FIG. 9 is an explanatory diagram of a power factor improving circuit applied to a ringing converter. The same functional portions as in FIG. 5 are denoted by the same reference numerals, and T3 denotes a transformer, R11 to R15.
Is a resistor, PC is a photocoupler, C11 and C12 are capacitors, Q5 is a transistor, and D5 is a diode.

When the transistor Q5 is off, a voltage is applied to the gate of the switching transistor Q1 via the resistor R11 to turn on, and the rectified output voltage of the rectifier circuit REC is applied to the primary winding of the transformer T3. The current flowing in the winding induces a voltage in the tertiary winding,
When the phototransistor of the photocoupler PC is off, an induced voltage is applied to the base of the transistor Q5 via the circuit of the resistors R13 and R14 and the capacitor C12, and the base voltage rises according to the CR time constant and rises above the threshold. The transistor Q5 is turned on, thereby decreasing the gate voltage of the switching transistor Q1, so that the switching transistor Q1 is turned off.

The induced voltage of the secondary winding of the transformer T3 due to the turning off of the switching transistor Q1 is rectified by the diode D1, and the capacitors C2 and C3 are charged.
The terminal voltage is applied to the load RL as a DC output voltage. The DC output voltage is detected by the resistors R1, R2, and R3 and compared with the reference voltage Vr by the operational amplifier OA1. For example, when the DC output voltage is high, the current flowing through the photodiode of the photocoupler PC via the resistor R15. And the current flowing through the phototransistor optically coupled to the photodiode is increased, whereby the time constant of the CR time constant circuit connected to the base of the transistor Q5 is equivalently reduced, and the base of the transistor Q5 is reduced. By increasing the voltage quickly and turning on the transistor Q5, the gate voltage of the switching transistor Q1 is reduced, and the switching transistor Q1 is turned off. That is, by shortening the on-period of the switching transistor Q1, it is possible to control the DC output voltage to a set value, as in the case of the pulse width control by the pulse width control circuit PWM.

Further, as in the case described above, the response speed of the error amplifier is increased to respond to the ripple voltage. However, the current is detected by the resistor R0 and input to the current feedback circuit FBK. Capacitor C3 for smooth output
The feedback voltage based on the current component flowing through the
A1 and the pulse width control circuit PW
A switching circuit Q1 is controlled by a control circuit including a transistor Q5 corresponding to M, so that the ON period of the switching transistor Q1 when the ripple voltage is at a low level is not widened, and a waveform of an AC current from the AC power supply. Is a substantially sinusoidal waveform to improve the power factor.

The present invention is not limited to the above embodiments, but is applicable to various types of switching power supply devices. Although the switching transistor Q1 is shown as a field effect transistor (FET), other types of switching elements can be used. Error amplifier and current feedback circuit FBK
It is also possible to apply another circuit type according to the characteristics of the operational amplifiers OA1 and OA2. Although the capacitors C2 and C3 are shown separately, it is of course possible to use one common capacitor.

[0043]

As described above, according to the present invention, the rectified output voltage Vin of the rectifier circuit REC is turned on and off by the switching transistor Q1, and the DC output voltage Vd of the terminal voltage of the smoothing output capacitor C3 is set to the set value. A power factor improving circuit of a switching power supply device that stabilizes the power supply so as to obtain a current feedback circuit FBK that detects a current flowing through a smoothing output capacitor and feeds back the current to an error amplifier. Speed up the DC output voltage V
In addition to stabilizing d, the low level of the ripple voltage is compensated so that the on / off period of the switching transistor Q1 is not affected by the ripple voltage Vrp, and the waveform of the AC current Iac from the AC power supply is substantially sinusoidal. There is an advantage that the power factor can be improved as a wavy shape.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

FIG. 2 is an operation explanatory diagram of the embodiment of the present invention.

FIG. 3 is an explanatory diagram of a power factor improvement circuit applied to a boost converter.

FIG. 4 is an explanatory diagram of a power factor improvement circuit applied to a buck-boost converter.

FIG. 5 is an explanatory diagram of a power factor improvement circuit applied to a forward converter.

FIG. 6 is an explanatory diagram of a power factor improvement circuit applied to a flyback converter.

FIG. 7 is an explanatory diagram of a power factor improvement circuit applied to a bridge converter.

FIG. 8 is an explanatory diagram of a power factor improvement circuit applied to a half-bridge converter.

FIG. 9 is an explanatory diagram of a power factor improvement circuit applied to a ringing converter.

FIG. 10 is an explanatory diagram of a conventional example.

FIG. 11 is an operation explanatory diagram of a conventional example.

[Explanation of symbols]

 Q1 Switching transistor REC Rectifier circuit C1, C2, C3, C5 Capacitor C3 Smoothing output capacitor RL Load L1, L2 Choke coil D1 Diode R0 to R9 Resistance OA1, OA2 Operational amplifier PWM Pulse width control circuit STG Sawtooth wave generator FBK Current feedback circuit

Claims (2)

[Claims] A switching transistor for turning on and off a rectified output voltage of a rectifier circuit for rectifying an AC voltage;
A smoothing output capacitor for applying a DC output voltage that increases as the ON period of the switching transistor increases to a load, an error amplifier for detecting an error between the DC output voltage and a set value, and an error amplifier. And a control circuit for controlling the on-period of the switching transistor in accordance with the error of the switching power supply. A power factor improving circuit, comprising: a current feedback circuit that feeds back to the error amplifier so as to compensate for a low level of a ripple voltage included in a voltage. 2. An operational amplifier for inputting a voltage between both ends of a resistor for detecting a current flowing through the smoothed output capacitor and the load, and an output signal of the operational amplifier via a capacitor, 2. The power factor correction circuit according to claim 1, further comprising a configuration for superimposing a part of the DC output voltage input to the error amplifier.