JP5222587B2 - Power factor correction circuit - Google Patents

Description

  The present invention relates to a power factor correction circuit in a step-up chopper type switching power supply device having a power factor improvement function.

  Switching power supply devices generally rectify commercial AC power, and output rectify the switching output obtained by switching the DC voltage with a switching element at a sufficiently high frequency compared to commercial AC frequency of 50 Hz or 60 Hz. It is supplied to a smoothing circuit and rectified and smoothed to obtain a desired arbitrary DC output voltage. Here, there are a classic configuration in which a smoothing circuit is provided after rectification of a commercial AC power supply, and a configuration without a smoothing circuit. If the smoothing circuit on the input side is a classic capacitor input type, there is a problem of lowering the power factor. First, a step-up chopper type switching power supply device having a power factor improvement function is provided in the previous stage, and then A method of obtaining a DC output of a desired voltage value by connecting a step-down switching power supply device to a stage has been adopted.

  A step-up chopper type switching power supply having a power factor improving function is generally composed of an inductor, a switching element, a rectifying / smoothing circuit, and a control circuit. A pulsating voltage obtained by rectifying an AC power supply is supplied to the inductor. The switching element switches the rectified voltage supplied through the inductor at a frequency sufficiently higher than the frequency of the commercial AC power supply, boosts and outputs the voltage. The rectifying and smoothing circuit rectifies and smoothes the switched output, converts the output to a DC voltage higher than the input rectified voltage, and outputs the DC voltage. Since the switching element switches the input rectified voltage at a frequency higher than the frequency of the AC power supply, boosts the voltage, and outputs it, the input current can be distributed and flowed over the entire period of one cycle of the AC power supply. The control circuit can improve the power factor of the switching power supply device by controlling the switching of the switching element so that the current flowing through the inductor is proportional to the voltage waveform of the AC power supply.

  Since the control circuit of the power factor correction circuit requires a large number of electronic circuits, a control IC is widely used. Prior inventions related to the power factor correction circuit are described in Patent Document 1, Patent Document 2, and Patent Document 3.

 Non-Patent Document 1 describes an example of a control circuit IC for a power factor correction circuit and a power factor correction circuit using the same. The control circuit IC includes a reference voltage source, an error amplifier having the reference voltage source connected to one end of the input terminal, a multiplier having the output of the error amplifier connected to one end of the input, and a multiplication thereof. A comparator for current comparison, the output of which is connected to one end of the input, a reference voltage source for zero current detection, a comparator for zero current detection in which this reference voltage source is connected to one end of the input terminal, It comprises a logic circuit that receives the output of the comparator for detecting zero current and the output of the comparator for comparing current. By using this control circuit IC to control the boost chopper circuit, switching can be performed in the critical mode. In addition, as for the control circuit IC of the power factor correction circuit described in Non-Patent Document 1, many other similar types are manufactured and marketed.

  Patent Document 1 discloses a boost chopper using a control IC, in which a series circuit of a capacitor and a first diode is connected in parallel to a switching element, and a second diode connected in series to the capacitor is provided. The anode side is connected to a connection point between the switching element and the current detection resistor, the cathode side is connected to the capacitor, and the second diode is connected to the connection point between the capacitor and the first diode on the anode side. A switching power supply is described in which the side is connected to the power supply terminal of the control IC. According to the present invention, stable operation can be ensured over a wide range of AC input voltage, and the control IC can always be operated normally even when the load fluctuates.

Patent Document 2 discloses a step-up chopper circuit in which a zero current detection circuit includes a DC blocking capacitor, a current limiting resistor, a level shift diode, and an impedance circuit. The DC blocking capacitor includes an auxiliary winding and a power supply for IC operation. The current limiting resistor is connected between one end of the auxiliary winding side of the DC blocking capacitor and the zero current detection terminal, and the level shift diode is connected between the other end of the DC blocking capacitor and the ground line. The DC blocking capacitor is charged with a voltage induced during the ON period of the switching element, and the charging voltage of the DC blocking capacitor is directed to be added to the smoothing capacitor during the OFF period of the switching element. The other end of the DC blocking capacitor is connected between the zero current detection terminal.
An impedance circuit applies a minute bias from the other end of the DC blocking capacitor to the zero current detection terminal. The potential of the zero current detection terminal is a potential obtained by adding a minute bias to the potential of one end of the DC blocking capacitor during the ON period of the switching element, and the addition amount increases when the instantaneous peak value of the AC input voltage is high. . For this reason, the potential of one end of the DC blocking capacitor can be set low, and the minimum potential difference between the instantaneous peak value of the AC input voltage and the DC output voltage can be reduced to about 25V.

The invention described in Patent Document 3 is a power factor correction circuit using a step-up chopper circuit, which is connected to switching element current detection means for detecting a current flowing in the switching element and a secondary winding, and the switching element is primary during the off period. Zero current detecting means for detecting that the current flowing through the winding has become zero, output voltage detecting means for detecting the output voltage of the switching element, voltage for turning on / off the switching element, and zero current detecting means Off time setting means for setting a time to turn off the switching element based on the detection result is provided.
According to the present invention, the off time of the switching element is set by providing the off time setting means for setting the time to turn off the switching element based on the detection results of the switching element current detecting means and the zero current detecting means. The switching power supply is shifted from the current critical switching power supply to the continuous current switching power supply, and a switching power supply capable of extracting a large amount of power without increasing the circuit scale can be provided.
JP 2001-286131 A JP 2004-350361 A JP 2006-296158 A Fuji Electric Co., Ltd. July 2002 Fuji Switching Power Supply Control IC Power Factor Correction IC FA5500A / FA5501A Application Note

  In the conventional power factor correction circuit, the power supply for operating the control circuit is obtained from the auxiliary winding of the inductor of the step-up chopper, or the minute energy related to the switching operation is skillfully used. At the same time, it is necessary to secure a condition for maintaining a zero current detection mechanism for making the input current a waveform close to each instantaneous value of the AC voltage and bringing the power factor close to 1. The present invention provides a power factor correction circuit having a degree of freedom in design that can satisfy even the most severe conditions with respect to the conditions related to the set value of the output voltage and the instantaneous peak value of the AC input voltage for the zero current detection switching operation. It is a problem to obtain.

  As a control mode of the power factor correction circuit, methods such as a critical value mode and an average value mode are practically used. The present invention relates to a power factor correction circuit that operates in the critical value mode. The power factor correction circuit operating in the critical value mode detects the current flowing through the inductor, and when the current flowing through the inductor decreases to zero, the switching element is turned on to operate the current flowing through the inductor in the critical value mode. The present invention is intended to maintain this critical value mode under a wide range of conditions.

  In the invention of Patent Document 2, the zero current detection switching operation has a degree of freedom in design in a wide range of conditions related to the set value of the output voltage and the instantaneous peak value of the AC input voltage. . In the present invention, the minimum potential difference of 25 V between the peak value of the AC input voltage and the output DC voltage is achieved. However, it is desirable to further expand the design conditions for the minimum potential difference between the peak value of the AC input voltage and the output DC voltage. An object of the present invention is to obtain a wide design freedom in a power factor correction circuit in a critical value mode.

In order to solve this problem, the present invention proposes the following means as the first means.
Rectifying means for rectifying and supplying AC voltage, an inductor having a main winding and an auxiliary winding coupled to the main winding, a switching element having a drive terminal and a pair of main current terminals, and the switching element And a control circuit that performs on / off switching control with a repetitive switching cycle shorter than the cycle of the AC voltage, and one end of the main winding of the inductor is connected to one end of the output of the rectifier and the main winding of the inductor The other end of the line is connected to the other end of the output of the rectifying means via the switching element and the current detecting means, and rectified from the connection point between the other end of the main winding of the inductor and the switching element. A power factor correction circuit that generates a DC output via an element,
The control circuit includes: a first reference voltage source; an error amplifier having the first reference voltage source connected to one end of an input terminal; and a multiplier having an output of the error amplifier connected to one end of an input; A first comparator having an output of the multiplier connected to one end of the input; a second reference voltage source; a second comparator having the second reference voltage source connected to one end of the input terminal; A logic circuit for receiving the output of the first comparator and the output of the second comparator;
The power supply for operating the control circuit is supplied from the auxiliary winding of the inductor via the auxiliary rectification means, and the rectification for each cycle corresponding to the switching period is independent from the auxiliary rectification means from the auxiliary winding. A power factor correction circuit is proposed which is connected to the other input terminal of the second comparator via a waveform shaping means including a diode.

The following means is proposed as the second means.
Rectifying means for rectifying and supplying AC voltage, an inductor having a main winding and an auxiliary winding coupled to the main winding, a switching element having a drive terminal and a pair of main current terminals, and the switching element And a control circuit that performs on / off switching control with a repetition cycle shorter than the cycle of the AC voltage, and one end of the main winding of the inductor is connected to one end of the output of the rectifying means and the main winding of the inductor the other end is connected to the other end of the output of said rectifying means via said switching element and the current detecting means, the rectifying element from a connection point between the other end of the main winding of the inductor and the switching element A power factor correction circuit that generates a DC output via
The control circuit includes: a first reference voltage source; an error amplifier having the first reference voltage source connected to one end of an input terminal; and a multiplier having an output of the error amplifier connected to one end of an input; A first comparator having an output of the multiplier connected to one end of the input; a second reference voltage source; a second comparator having the second reference voltage source connected to one end of the input terminal; A logic circuit for receiving the output of the first comparator and the output of the second comparator;
A voltage feedback input terminal 1 connected to one end of the input terminal of the error amplifier for stabilizing the output voltage;
An output terminal 2 of the error amplifier;
A multiplier input terminal 3 connected to one end of the input terminal of the multiplier and for inputting a sinusoidal AC power supply waveform;
A current detection terminal 4 connected to the other end of the input terminal of the first comparator for detecting the current of the switching element;
A zero current detection terminal 5 connected to the other input terminal of the second comparator for detecting that the current of the inductor has returned to zero;
A ground terminal 6 of the control circuit;
A control output terminal 7 for driving the switching element;
A control circuit comprising a power input terminal 8 for operating the control circuit,
The connection relationship of each terminal of the control circuit is
The voltage feedback input terminal 1 is connected to one end of the DC output via a voltage dividing means,
The multiplier input terminal 3 is connected to one end of the output of the rectifying means via a voltage dividing means,
The current detection terminal 4 is connected to a connection point between the main current terminal of the switching element and the current detection means,
The zero current detection terminal 5, the first resistor and via the second resistor is connected to one end of the auxiliary winding of the inductor, the the first resistor capacitor connected in series with each other When connected in parallel together, said first resistor and a second diode between a connection point between the resistor the ground terminal 6 is connected,
A power ground terminal 6 is connected to one end of the other output terminal of the rectifying means,
The control output terminal 7 is connected to a drive terminal of the switching element;
A power supply input terminal 8 for operating the control circuit is connected to one end of the rectifier means via a high-resistance resistor for starting, and a second rectifier is connected to one end of the auxiliary winding of the inductor. Connected through means,
A power factor correction circuit characterized by that.

  Further, as a third means, in addition to the second means, a diode connected between the connection point of the first resistor and the second resistor and the ground terminal 6 is further connected in series. It is proposed that three resistors be connected.

  As a fourth means, a Zener diode is proposed to be connected between the multiplier input terminal 3 and the power supply ground terminal 6 in addition to the second means or the third means.

  The present invention is connected to the zero current detection control from the auxiliary winding of the inductor through the waveform shaping means including the rectifying diode for each period corresponding to the switching period independently from the auxiliary rectifying means for the control circuit. As a result, with regard to the zero current detection switching operation, power factor improvement with design flexibility that can satisfy even the most severe conditions regarding the conditions related to the set value of the output voltage and the instantaneous peak value of the AC input voltage A circuit can be obtained.

The circuit diagram shown in FIG. 1 is a schematic diagram of a power factor correction circuit according to the present invention, and is a power factor correction circuit in a switching power supply device using a critical mode power factor correction IC. The main configuration of this circuit includes a bridge-type rectifier circuit REC1, which is a rectifier that rectifies and supplies an AC voltage Vac, and a main winding Np and an auxiliary winding Ns coupled to the main winding. An inductor L1, a switching element Q1 having a drive terminal and a pair of main current terminals, and a control circuit IC that performs on / off switching control of the switching element Q1 in a repetition cycle shorter than the cycle of the AC voltage Vac. One end of the main winding Np is connected to one end of the output of the rectifier circuit REC1, and the other end of the main winding Np of the inductor L1 is connected via the switching element Q1 and a low-resistance resistor R15 that is a current detection means. It is connected to the other end of the output of the rectifier circuit REC1 Te, or the connection point between the other end and switching elements of the main winding Np of the inductor L1 It is configured to via a diode D11 to generate a DC output from an output terminal 201 and 202.

  FIG. 10 is a schematic circuit block of the control circuit IC of the power factor correction circuit. The control circuit IC includes a first reference voltage source 102, an error amplifier 101 having the first reference voltage source 102 connected to one end of an input terminal, and an output of the error amplifier 101 having one end of an input. , The first comparator 104 whose output is connected to one end of the input, the second reference voltage source 106, and the second reference voltage source 106 are input terminals. And a logic circuit 107 and 117 that receives the output of the first comparator 104 and the output of the second comparator 105.

  In the circuit shown in FIG. 1, the operation power supply of the control circuit IC is supplied from a bridge-type rectifier circuit REC1, which is a rectifier that rectifies and supplies the AC voltage Vac at the time of startup. The starting resistor R6 supplied to the terminal 8 of the control circuit IC via the resistor R6 is a high-resistance resistor that supplies the minimum power necessary for starting, and will be described below. The control circuit IC is used for supplying small energy until the power supply for its operation is completely started up.

  In FIG. 1, when the control circuit IC rises, the switching element Q1 of the main circuit is turned on, and a current flows from the inductor L1 to the switching element Q1. This current is detected by the current detection terminal 4 (IS). When the detected current value exceeds the reference value determined by the error signal between the output voltage and the reference voltage and the output of the multiplier having the input voltage signal as an input, the switching element Q1 is turned off, and the on period is finish. When the switching element Q1 is turned off, the potential of the inductor L1 is inverted, and current is supplied from the inductor L1 to the output side via the diode D1.

In the critical mode operation, it is necessary to turn on the switching element Q1 again when the current supplied from the inductor L1 returns to zero. The critical mode control circuit IC is provided with a zero current detection terminal (ZCD) for detecting this timing. The zero current detection terminal is connected to the auxiliary winding Ns provided in the inductor L1 via the limiting resistor R1.
When the current of the inductor L1 becomes zero, the voltage between the terminals of the inductor L1 is attenuated and oscillated by the action of the resonance circuit composed of the inductance of the inductor L1 and the floating capacitance in the circuit, and the voltage decreases. Follow the course. In the critical mode control IC, the voltage of the voltage across the terminal of the lowering inductor L1 is detected from the coupled auxiliary winding Ns, and the inductor Q1 is turned on again. By repeating the above operation, the power factor improving converter using the critical mode power factor improving IC continues its switching operation at a sufficiently high variable frequency compared with the frequency of the AC input.

  When a control IC is used, a power source for operating the electronic circuit of the control IC itself is necessary. Conventionally, as shown in FIG. 11, control is performed using an auxiliary winding Ns of an inductor L1. An IC power supply can be formed, and this method is often used. As shown in FIG. 11, when a supply source is obtained from only one auxiliary winding Ns of the inductor and the circuit configuration is made common for the zero current detection and the power supply for the control IC, there is a limitation. Come on.

  The waveform diagram shown in FIG. 2 conceptually shows the voltage waveform of the auxiliary winding Ns (point r in FIG. 1) of the inductor L1. When the angular frequency of the AC input voltage is represented by ω, if the voltage (instantaneous value of the input voltage) applied to the inductor L1 is (Vin × sin (ωt)), the envelope of the voltage generated in the auxiliary winding Ns is It is expressed by Equation (1). Note that the interval where the input voltage is negative is considered as its absolute value.

  env = (Vout−Vin × sin (ωt)) × (Ns / Np) (1)

here,
env: voltage value of envelope Ns: number of turns of auxiliary winding of inductor L1 Np: number of turns of main winding of inductor L1 From this equation (1), the value of the positive potential generated in auxiliary winding Ns of inductor L1 is It can be seen that the AC input voltage waveform has the lowest peak value of the instantaneous peak value, and the higher the AC input voltage, the lower the value.
At a high input voltage, the following relationship is established.

(Vout−Vin × sin (ωt)) × (Ns / Np) <zero current detection voltage (2)

  The voltage generated in the auxiliary winding Ns does not satisfy the necessary condition for zero current detection because of the relationship of the expression (2).

  In FIG. 3, the voltage generated from the auxiliary winding Ns of the inductor shows an enlarged waveform of one cycle of the switching element. At this time, the voltage of the auxiliary winding Ns of the inductor below the threshold of the zero current detection voltage does not exceed the zero current detection level, so the timing of turning on or turning off earlier than usual is greatly delayed. In other words, stable operation cannot be performed.

  In the circuit of FIG. 1 of an embodiment of the power factor correction circuit according to the present invention, first, a circuit in which a diode D1, a capacitor C1, and a resistor R2 are added is considered, and a circuit without the resistor R3 is considered.

  The capacitor C1 has a voltage ((Vin) × (Ns / Np) shown in FIG. 2) generated in the auxiliary winding Ns when the switching element Q1 is turned on. ) × (Ns / Np) × sin (ωt)) is charged via the diode D1. Note that the interval where the input voltage is negative is considered as its absolute value. The resistor R2 functions to prevent noise at the time of charging, but a value sufficiently small with respect to the value of the resistor R1 is ideal so as not to affect the operation of the zero current detection terminal. Further, the value of the resistor R2 can be short-circuited with zero.

Next, when the switching element Q1 is turned off, the voltage of the auxiliary winding Ns of the inductor (point r, (Vout−Vin) × (Ns / Np of FIG. 2) is applied to one terminal (point s) of the resistor R1. Voltage)) and the voltage of the capacitor C1 are generated. The instantaneous value of Vin is correctly a sine wave function depending on the frequency of the AC input, but is omitted here.

The voltage generated at the point s in the same operation state as that of the waveform diagram shown in FIG. 3 is as shown in the waveform of FIG.
The zero current detection terminal has a built-in clamp circuit for terminal protection.
When the voltage applied to the zero current detection terminal is higher than the clamp voltage, a clamp current flows through the limiting resistor R1.
At this time, since the discharge current flows from the capacitor C1, the voltage of the capacitor C1 decreases.

This is why the voltage at the point s shown in FIG.
When the voltage at point s drops to the clamp voltage, the discharge of the capacitor C1 is almost eliminated, so that the voltage is almost flat.

  Thereafter, when the current of the inductor L1 becomes zero and the voltage (point r) of the auxiliary winding Ns of the inductor L1 decreases, the voltage at the point s reaches the zero current detection voltage and the switching element Q1 is normally turned on. It becomes possible.

Consider a case where the difference between the instantaneous peak value of the AC input voltage (Vac) and the output voltage (Vout) becomes smaller than the condition of FIG.
At this time, the value of the positive potential generated in the auxiliary winding Ns of the inductor is further reduced, and the amount of voltage drop of the auxiliary winding Ns when the current flowing through the inductor L1 becomes zero is also reduced.
If the residual voltage of the capacitor C1 becomes larger than the voltage drop value of the auxiliary winding Ns, even if the voltage of the auxiliary winding Ns as shown in FIG. The current detection voltage does not drop and zero current cannot be detected.
At this time, the switching element Q1 cannot be turned on at regular timing, and stable operation cannot be performed.

Next, consider a circuit in which a resistor R3 exists as shown in the circuit of FIG. The resistor R3 functions as a discharge resistor for the capacitor C1. The discharge time of the capacitor C1 is determined by adjusting the value of the capacitor C1 and the value of the resistor R3.
By adjusting the residual voltage of the capacitor C1 in accordance with the amount of decrease in the voltage of the auxiliary winding Ns at zero current according to this discharge time, the operation shown in FIG. 6 can be performed under the same operating conditions as those shown in FIG. The operation is the same, zero current can be detected normally, and stable operation can be obtained.
By selecting appropriate values for the capacitor C1 and the resistor R3 in this way, stable operation can be obtained until the difference between the peak value of the AC input voltage (Vac) and the output voltage (Vout) approaches zero. It becomes.

  FIG. 7 shows a second embodiment of the present invention.

As a second embodiment of the present invention, a resistor R4 is additionally connected to the embodiment shown in FIG. In the circuit shown in FIG. 7, the resistor R4 can determine the time constant for charging the capacitor C1 during the ON period of the switching element Q1.
In the circuit shown in FIG. 1, since the capacitor C1 is charged to Vin × (Ns / Np) when the switching element Q1 is turned on, the discharge time of the capacitor C1 changes according to the change of Vin.

FIG. 8 shows a voltage change between the terminals of the capacitor C1 during the operation shown in FIG.
In the circuit of FIG. 7 of the second embodiment of the present invention, since there is a time constant circuit with the resistor R4, the charging voltage of the capacitor C1 can be changed by the ON time of the switching element Q1.

FIG. 9 shows a voltage waveform between the C1 terminals in comparison with FIG.

  In the critical mode power factor correction converter, the switching frequency changes depending on the input conditions and load conditions. In the second embodiment shown in FIG. 7, by providing the resistor R4, in addition to the change due to Vin, the discharge time of the capacitor C1 can be changed in response to the change in the ON time of the switching element. For this reason, the setting for obtaining stable operation in a wide range can be further facilitated by the action of the circuit including the resistor R4.

For the fourth means of the present invention, there is a slight efficiency improvement.
A zener diode ZD1 is connected in parallel to the detection portion of the waveform of the AC input voltage to detect the input voltage waveform. At this time, even if the detection voltage becomes the Zener voltage of the Zener diode ZD1, it is not completely clamped, but the AC input sine wave waveform is maintained to some extent depending on the current-voltage characteristics between the terminals of the Zener diode. Acts like This waveform is a waveform of a pseudo sine wave whose head is slightly crushed rather than a complete sine wave. Since the input current is controlled to resemble the waveform of this pseudo sine wave, the current peak value is suppressed compared to the case without the Zener diode ZD1, the effective current value is suppressed, and the efficiency is improved. The effect is obtained. Therefore, when the AC input voltage is high, the input voltage to the multiplier can also be suppressed. Therefore, within a wide range of the AC input voltage, within the allowable input voltage range of the input terminal of the multiplier of the control circuit, the range. It is possible to design using the maximum.

The operation mode according to the present invention
An embodiment of a critical mode power factor correction circuit according to the present invention Voltage waveform corresponding to the period of the input AC voltage of the auxiliary winding of the inductor Voltage waveform corresponding to the switching period of the auxiliary winding of the inductor Voltage waveform of the operation mode according to the present invention of the auxiliary winding of the inductor In the waveform diagram for explanation leading to the present invention, an example in which the operation mode is faulty Voltage waveform of the operation mode according to the present invention of the auxiliary winding of the inductor Second embodiment of critical mode power factor correction circuit according to the present invention Voltage waveform corresponding to the switching period of the auxiliary winding of the inductor Voltage waveform corresponding to the switching period of the auxiliary winding of the inductor Outline circuit block of control circuit IC for power factor correction circuit Example of conventional critical mode power factor correction circuit

Explanation of symbols

IC for control circuit
Vac AC power supply REC1 Rectifier circuit 100 Common line 201, 202 Output terminal L1 Inductor Np Inductor main winding Ns Inductor auxiliary winding Q1 Switching element

Claims (4)

Rectifying means for rectifying and supplying AC voltage, an inductor having a main winding and an auxiliary winding coupled to the main winding, a switching element having a drive terminal and a pair of main current terminals, and the switching element And a control circuit that performs on / off switching control with a repetitive switching cycle shorter than the cycle of the AC voltage, and one end of the main winding of the inductor is connected to one end of the output of the rectifier and the main winding of the inductor The other end of the line is connected to the other end of the output of the rectifying means via the switching element and the current detecting means, and rectified from the connection point between the other end of the main winding of the inductor and the switching element. A power factor correction circuit that generates a DC output via an element,
The control circuit includes: a first reference voltage source; an error amplifier having the first reference voltage source connected to one end of an input terminal; and a multiplier having an output of the error amplifier connected to one end of an input; A first comparator having an output of the multiplier connected to one end of the input; a second reference voltage source; a second comparator having the second reference voltage source connected to one end of the input terminal; A logic circuit for receiving the output of the first comparator and the output of the second comparator;
The power supply for operating the control circuit is supplied from the auxiliary winding of the inductor via the auxiliary rectification means, and the rectification for each cycle corresponding to the switching period is independent from the auxiliary rectification means from the auxiliary winding. A power factor correction circuit, wherein the power factor correction circuit is connected to another input terminal of the second comparator via a waveform shaping means including a diode.

Rectifying means for rectifying and supplying AC voltage, an inductor having a main winding and an auxiliary winding coupled to the main winding, a switching element having a drive terminal and a pair of main current terminals, and the switching element And a control circuit that performs on / off switching control with a repetition cycle shorter than the cycle of the AC voltage, and one end of the main winding of the inductor is connected to one end of the output of the rectifying means and the main winding of the inductor the other end is connected to the other end of the output of said rectifying means via said switching element and the current detecting means, the rectifying element from a connection point between the other end of the main winding of the inductor and the switching element A power factor correction circuit that generates a DC output via
The control circuit includes: a first reference voltage source; an error amplifier having the first reference voltage source connected to one end of an input terminal; and a multiplier having an output of the error amplifier connected to one end of an input; A first comparator having an output of the multiplier connected to one end of the input; a second reference voltage source; a second comparator having the second reference voltage source connected to one end of the input terminal; A logic circuit for receiving the output of the first comparator and the output of the second comparator;
A voltage feedback input terminal 1 connected to one end of the input terminal of the error amplifier for stabilizing the output voltage;
An output terminal 2 of the error amplifier;
A multiplier input terminal 3 connected to one end of the input terminal of the multiplier and for inputting a sinusoidal AC power supply waveform;
A current detection terminal 4 connected to the other end of the input terminal of the first comparator for detecting the current of the switching element;
A zero current detection terminal 5 connected to the other input terminal of the second comparator for detecting that the current of the inductor has returned to zero;
A ground terminal 6 of the control circuit;
A control output terminal 7 for driving the switching element;
A control circuit comprising a power input terminal 8 for operating the control circuit,
The connection relationship of each terminal of the control circuit is
The voltage feedback input terminal 1 is connected to one end of the DC output via a voltage dividing means,
The multiplier input terminal 3 is connected to one end of the output of the rectifying means via a voltage dividing means,
The current detection terminal 4 is connected to a connection point between the main current terminal of the switching element and the current detection means,
The zero current detection terminal 5, the first resistor and via the second resistor is connected to one end of the auxiliary winding of the inductor, the the first resistor capacitor connected in series with each other When connected in parallel together, said first resistor and a second diode between a connection point between the resistor the ground terminal 6 is connected,
A power ground terminal 6 is connected to one end of the other output terminal of the rectifying means,
The control output terminal 7 is connected to a drive terminal of the switching element;
A power supply input terminal 8 for operating the control circuit is connected to one end of the rectifier means via a high-resistance resistor for starting, and a second rectifier is connected to one end of the auxiliary winding of the inductor. Connected through means,
A power factor correction circuit characterized by that.
  The third resistor is further connected in series to a diode connected between a connection point between the first resistor and the second resistor and the ground terminal. 2. The power factor correction circuit according to 2.   4. The power factor correction circuit according to claim 2, wherein a Zener diode is connected between the multiplier input terminal 3 and the power supply ground terminal 6. 5.

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