JPH09252578A - Higher harmonic current reducing circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a higher harmonic current reducing circuit where the drop of the conversion efficiency is improved, and the number of part items is reduced, and the econommzataon is achieved. SOLUTION: AC voltage from an AC power source 1 is half-wave-rectified with a rectifier diode 2, and this half-wave rectified voltage is switched with a switching element, and it is smoothed with an electrolytic capactor 12 through a high-speed recovery diode 8 before supply to a load 13, and also the switching element 9 is turned on/off so that the current from the AC power source may be sine waves through a drive circuit 10, based on the input voltage from an input voltage detecting circuit 5, the input current from an input current detecting circuit 7, and the output current from an output voltage detecting means 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention rectifies an AC voltage from an AC power supply, switches the rectified voltage, and rectifies the switched voltage to reduce a harmonic current in a power supply circuit. The present invention relates to a harmonic current reduction circuit.

[0002]

2. Description of the Related Art In recent years, active filters have been developed that comply with domestic and overseas regulations on power supply harmonic currents, and as a harmonic current reduction circuit using such an active filter, a conventional one as shown in FIG. is there. The harmonic current reduction circuit shown in FIG. 11 rectifies the AC voltage (waveform shown by the dotted line in FIG. 12) from the AC power supply 91 by the full-wave rectification circuit 92 composed of four diodes, and the rectified voltage is the reactor. The voltage is switched by the switching transistor 94 via 93, the switched voltage is rectified by the diode 95, and the load 9 is rectified via the smoothing capacitor 96.
It supplies to 7.

Also, the input voltage from the input voltage detection circuit 98, the input current from the input current detection circuit 99, and the output voltage from the output voltage detection circuit 102 are supplied to the active filter control circuit 103, and the active filter control circuit 1 is supplied.
The ON / OFF switching of the switching transistor 94 is performed by the output signal from the drive circuit 101 through the drive circuit 101 so that the power supply current waveform shown by the solid line in FIG. 12 becomes the same sine wave as the power supply voltage waveform shown by the dotted line. However, the harmonic components of the power supply current are reduced.

[0004]

As described above, when an active filter is used to reduce the harmonic current, it causes an increase in cost and a decrease in conversion efficiency as compared with the conventional power supply circuit, which is an obstacle to practical use. Has become. The cause of lowering the conversion efficiency is mainly the diode, the reactor and the switching element.

In particular, in the conventional circuit, as shown in FIG. 11, the AC voltage from the AC power supply 91 is rectified by the full-wave rectification circuit composed of four diodes, so that the switching transistor 94 is turned on in FIG. The two diodes are inserted in the current loop indicated by the dotted line during the period during which the current is flowing, and the three diodes are inserted in the current loop during the off period, which lowers the conversion efficiency and
There are many parts and it is uneconomical.

[0006] The present invention has been made in view of the above,
It is an object of the present invention to provide a harmonic current reduction circuit that improves the reduction in conversion efficiency, reduces the number of parts, and is economical.

[0007]

In order to achieve the above object, the present invention according to claim 1 provides a rectifying diode connected to one end of an AC power supply for half-wave rectifying the AC voltage from the AC power supply, A reactor connected in series with the rectifier diode, a high speed recovery diode connected in series with the reactor, and a load connected in parallel between the other end of the high speed recovery diode and the other end of the AC power supply. An electrolytic capacitor, a switching element connected to the load side of the reactor, a resistor connected between the load side of the rectifying diode and the other end of the AC power supply, and connected to the resistor, from the AC power supply Input voltage detection circuit for detecting the input voltage of the AC power supply, an input current detection circuit for detecting the current from the AC power supply, a drive circuit for driving the switching element, The output voltage detection means for detecting the voltage across the capacitor, the input voltage detection circuit, the input current detection circuit, based on the output signal from the output voltage detection circuit, the current from the AC power supply becomes a sine wave Thus, the gist of the present invention is to have a control circuit that supplies a signal for driving the switching element on / off to the drive circuit.

According to the first aspect of the present invention, the AC voltage from the AC power source is half-wave rectified by the rectifier diode, and the half-wave rectified voltage is switched by the switching element via the reactor to provide the high-speed recovery diode. It is smoothed by an electrolytic capacitor to supply to the load via the input voltage detection circuit, the input current from the input current detection circuit, and the output current from the output voltage detection means. The switching element is driven on / off so that the current of 1 becomes a sine wave.

According to a second aspect of the present invention, a reactor connected to one end of an AC power supply, a fast recovery diode connected in series with the reactor, the other end of the fast recovery diode and the AC power supply. An electrolytic capacitor connected in parallel to the load between the other end, a switching element connected to the load side of the reactor, a protection diode connected in series to the switching element, and a series connection at both ends of the AC power supply. A rectifying diode and a resistor connected to the resistor, an input voltage detection circuit connected to the resistor for detecting an input voltage from the AC power supply, an input current detection circuit for detecting a current from the AC power supply, and the switching element. A drive circuit for driving the output capacitor, output voltage detecting means for detecting the voltage across the electrolytic capacitor, the input voltage detecting circuit, A control circuit that supplies a signal for driving the switching element to ON / OFF to the drive circuit based on an output signal from the input current detection circuit and the output voltage detection circuit so that the current from the AC power supply becomes a sine wave. The point is to have and.

According to the second aspect of the present invention, the AC voltage from the AC power source that has passed through the reactor is switched by the switching element through the protection diode, and the switched voltage is passed through the fast recovery diode and the electrolytic capacitor. The output voltage from the AC voltage from the AC power supply is detected by the input voltage detection circuit via the diode and the resistor, the input current from the input current detection circuit, and the output from the output voltage detection means. The switching element is driven on / off based on the current so that the current from the AC power supply becomes a sine wave via the drive circuit.

Further, the present invention according to claim 3 provides the invention according to claim 2.
In the invention described above, the input voltage detection circuit is a photodiode connected in series to the resistor and a photocoupler optically connected to the photodiode, and a phototransistor for outputting a phase detection signal, and the phase detection signal. A counter that detects the difference between the time when the level is high and the time when the level is low, a shift register that is loaded with the count value of the counter, and shifts the count value, and a count value of the counter and a register of the shift register. The gist is to have a comparator that compares the value with a value and detects the zero-cross point of the AC power supply.

According to another aspect of the present invention, a counter detects the difference between the time when the phase detection signal from the photocoupler is at the high level and the time when the phase detection signal from the photocoupler is at the input voltage detection circuit. The count value is loaded into the shift register and shifted, the count value of the counter and the register value of the shift register are compared, and the zero-cross point of the AC power supply is detected.

According to a fourth aspect of the present invention, in the invention according to the second aspect, the drive circuit compares a voltage obtained by half-wave rectifying the AC voltage from the AC power source with a predetermined reference voltage to output a phase detection signal. It is a gist to have a comparator which is generated and an AND circuit which takes a logical product of the phase detection signal and the drive signal output from the comparator.

According to the present invention of claim 4, in the drive circuit, a voltage obtained by half-wave rectifying the AC voltage from the AC power source is compared with a predetermined reference voltage to generate a phase detection signal, and the phase detection signal is detected. An AND circuit takes the logical product of the signal and the drive signal.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing the configuration of a harmonic current reducing circuit according to an embodiment of the present invention. The harmonic current reduction circuit shown in FIG. 1 includes a rectifier diode 2 for half-wave rectifying an AC voltage from an AC power supply 1, a reactor 3 having one end connected to the anode of the rectifier diode 2, and a cathode at the other end of the reactor 3. Is connected to the cathode of the fast recovery diode 8, one end of which is connected to the cathode of the fast recovery diode 8 and the load 13 is connected to both ends of the electrolytic capacitor 12, the cathode of the rectifier diode 2 and the other end of the AC power supply 1. Two voltage-dividing resistors 4a, 4b connected in series, one end of which is connected to the other end of the AC power supply 1, and one end of which is connected to the other end of the current detection resistor 6 and the reactor. IGBT or MOSF connected between the other end
Switching element 9 made of ET or the like, the voltage dividing resistor 4
an input voltage detection circuit 5 connected to the connection point of a and 4b for detecting an input voltage; an input current detection circuit 7 connected to both ends of the current detection resistor 6 for detecting an input current; and a base of the switching element 9. Drive circuit 1 connected to
0, an output voltage detection circuit 11 that detects the output voltage across the electrolytic capacitor 12, an input voltage from the input voltage detection circuit 5, an input current from the input current detection circuit 7, and an output voltage from the output voltage detection circuit 11. And a harmonic current reduction control circuit 14 for outputting to the drive circuit 10 a control signal for on / off driving the switching element 9 so that the current of the AC power supply 1 becomes a sine wave based on each of these input signals. It consists of

FIG. 2 shows the harmonic current reduction control circuit 14 used in the harmonic current reduction circuit shown in FIG.
FIG. 3 is a block diagram showing a detailed configuration of FIG. The harmonic current reduction control circuit 14 shown in FIG.
Error amplifier 22 for calculating the output voltage from the reference voltage source and the reference voltage from the reference voltage source 21, the output of the voltage error amplifier 22 and the reference voltage waveform fetched from the input voltage detection circuit 5, and the reference voltage waveform , A current error amplifier 25 for calculating a reference current waveform from the multiplier 23 and an input current waveform from the input current detection circuit 7, and an output signal from the current error amplifier 25 from a PWM frequency oscillator 24. A PWM comparator 26 that compares the generated PWM signal with the generated PWM signal, and a protection circuit 27 that protects the PWM signal from the overvoltage, overcurrent, etc., and outputs the PWM signal from the PWM comparator 26 to the drive circuit 10. Has been done.

FIG. 3 is a diagram showing a power supply voltage waveform and a power supply current waveform in the harmonic current reducing circuit of FIG. 1. The dotted line is the power supply voltage waveform seen from point B to A in FIG. 1, and the solid line is the power supply current. The waveform is shown.

In the harmonic current reducing circuit configured as described above, the AC voltage from the AC power source 1 (voltage shown by the dotted line in FIG. 3) is half-wave rectified by the rectifying diode 2, and this half-wave rectification is performed. The voltage is switched by the switching element 9 via the reactor 3, and the switched voltage is rectified by the fast recovery diode 8, smoothed by the electrolytic capacitor 12, supplied to the load 13, and rectified by the rectifying diode 2. The generated voltage is a voltage dividing resistor 4
The voltage is divided by a and 4b and detected by the input voltage detection circuit 5,
The input voltage detection circuit 5 supplies a reference voltage waveform as shown in FIG. 4A to the harmonic current reduction control circuit 14.

Since the AC voltage from the AC power supply 1 is half-wave rectified by the rectifying diode 2, the input voltage detection circuit 5 has only a half power supply cycle, that is, the power supply cycle 360, as shown in FIG. 4A. The output signal is generated only during a period of 0 to 180 degrees. Therefore, the input current detected by the input current detection circuit 7 is also 0 to 18 as shown by the solid line in FIG.
Only a half cycle of 0 degrees flows.

The input current detection circuit 7 detects the power supply current waveform by the voltage drop of the current detection resistor 6 and supplies it to the harmonic current reduction control circuit 14. The harmonic current reduction control circuit 14, when the phase of the power supply voltage is 0 degrees to 180 degrees,
A PWM signal is output from the drive circuit 10 to turn on / off the switching element 9, and the power supply current waveform is controlled to be the same sine wave as the reference voltage waveform. The PWM signal is
When the power supply current waveform is smaller than the reference current waveform, the switching element 9 is turned off and the energy of the reactor 3 is released. This operation is repeated at the PWM frequency, and PWM control is performed so that the power supply current waveform and the reference voltage waveform have the same sine wave.

The PWM frequency is the PWM frequency oscillator 24.
Occurs and is set from several tens KHz to several hundred KHz. Further, the harmonic current reduction control circuit 14 controls the output voltage to be constant. The output voltage detection circuit 11 detects the output voltage across the electrolytic capacitor 12 by dividing the voltage across the resistor.

The harmonic current reduction control circuit 14 calculates the output voltage detected by the output voltage detection circuit 11 and the reference voltage of the reference voltage source 21 inside the harmonic current reduction control circuit 14 by the voltage error amplifier 22. The multiplier 23 calculates the output of the voltage error amplifier 22 and the reference voltage waveform fetched from the input voltage detection circuit 5, and outputs the reference current waveform. Multiplier 23
Calculates when the output voltage is low, the reference current waveform is large, and when the output voltage waveform is high, the reference current waveform is small. As a result, even if the load current changes,
The output voltage can be controlled to be constant.

The rectifier diode 2 half-wave rectifies the AC voltage from the AC power supply 1, and the power supply voltage has a phase of 18
It acts so as to prevent the reverse voltage from being applied to the switching element 9 in the range of 0 to 360 degrees. In addition,
The harmonic current reduction control circuit 14 can use an active filter control IC which has been conventionally commercialized.

In the harmonic current reduction circuit configured as described above, the power supply voltage from the AC power supply 1 can be rectified by one rectifying diode 2, and the conventional circuit shown in FIG. Three diodes can be eliminated compared to what was needed. Further, in the configuration of the conventional active filter, while the switching element 9 is on, two diodes are inserted in the current loop as described with reference to FIG. In the harmonic current reducing circuit of the present embodiment, when the switching element 9 is on, only one diode 2 is inserted in the current loop, and during the off period, the two diodes 2, 2. 8 has been inserted. Therefore, the loss due to the forward voltage drop of the diode becomes 1/2 during the period when the switching element 9 is on, and becomes 2/3 during the period when the switching element 9 is off, and the reduction of the conversion efficiency can be improved.

FIG. 5 is a circuit diagram showing the configuration of a harmonic current reducing circuit according to another embodiment of the present invention. In the harmonic current reducing circuit shown in the figure, the rectifying diode 2 is deleted from the embodiment shown in FIG. 1, and instead, the rectifying diode 16 is inserted in series in the voltage dividing resistors 4a and 4b connected in series to perform switching. Protection diode 1 in series with element 9
5 is inserted, and other configurations are the same as those in FIG.

In the harmonic current reducing circuit configured as shown in FIG. 5, the current flowing through the rectifying current 16 connected in series with the voltage dividing resistors 4a and 4b is as small as a few mA, so that the diode 16 has a small signal. Inexpensive diodes can be used. Further, the power supply current always flows through the rectifying diode 2 in the circuit of FIG. 1, but in the circuit of FIG. 5, a current flows through the protection diode 15 only when the switching element 9 is on. Therefore, while the switching element 9 is on, one diode is inserted in the current loop as in the circuit of FIG. 1, but one diode is inserted in the current loop during the off period. Will be inserted.
Therefore, the loss due to the forward voltage drop of the diode is 1/2 when the switching element 9 is on and 1 when the switching element 9 is off, as compared with the conventional configuration shown in FIG.
It becomes / 3, and the conversion efficiency can be further improved as compared with the configuration of FIG.

FIG. 6 is a circuit diagram showing the configuration of a harmonic current reducing circuit according to still another embodiment of the present invention. The harmonic current reducing circuit shown in the figure is different only in that the positions of the switching element 9 and the protection diode 15 are replaced with each other in the embodiment shown in FIG. 5, and other configurations and actions are the same as those shown in FIG. Is. Therefore, the harmonic current reduction circuit of FIG. 6 can also realize the same operation as the circuit of FIG.
Similar effects can be achieved.

FIG. 7 is a circuit diagram showing the configuration of a harmonic current reducing circuit according to another embodiment of the present invention. The harmonic current reduction circuit shown in the figure is different only in that the connection position of the reactor 3 and the fast recovery diode 8 is moved to the lower side in the embodiment shown in FIG. It is the same as the one. Therefore, the harmonic current reducing circuit of FIG. 7 can also realize the same operation as that of the circuits of FIG. 5 and FIG. 6 and the same effect.

FIG. 8 is a circuit diagram showing the configuration of a harmonic current reducing circuit according to still another embodiment of the present invention. The harmonic current reducing circuit shown in the figure is different only in that the positions of the switching element 9 and the protection diode 15 are exchanged in the embodiment of FIG. 7, and other configurations and actions are the same as those of FIG. 7. Therefore, the harmonic current reducing circuit shown in FIG. 8 can also realize the same operation as that of the circuit of FIG. 7 and the same effect.

FIG. 9A is a diagram showing another configuration of the input voltage detection circuit 5 in each of the embodiments shown in FIGS. 5 to 8. A method has been proposed in which the reference current waveform (sine wave) of the harmonic current reduction circuit is stored in a memory inside the harmonic current reduction circuit and is output in synchronization with the zero-cross point of the AC power supply. In this case,
It suffices to detect the zero-cross point of the AC power supply.

In FIG. 9, the AC voltage from the AC power supply 1 is applied to the photodiode 32a of the photocoupler 32 through the resistor 31, and the photodiode 32a is shown in FIG. As described above, the current flows only in the positive half cycle, whereby the phototransistor 32b of the photocoupler 32 becomes conductive, and the phase detection signal as shown in (b) of FIG. 9B is output from the phototransistor 32b. . The collector of the phototransistor 32b is pulled up to a power supply voltage (not shown) by a pullup resistor 33.

The phase detection signal output from the phototransistor 32b is supplied to the counter 34, which resets the counter 34 at the rising edge of the phase detection signal as shown in (c) of FIG. 9B. , The counter is started to count up, and the counter is down-counted at the falling edge. Then, at the next rising edge, the count value of the counter 34 is loaded into the shift register 35 and is shifted by 2 bits to make the value of the shift register 35 ¼. Counter 3
4 and each value of the shift register 35
The comparator 36 compares the two values and outputs the time when the two values match as a zero-cross point as shown in (d) of FIG. 9B. The harmonic current reduction control circuit 14 outputs the PWM signal from the drive circuit 10 in synchronization with this zero-cross point as shown in (e) of FIG. 9B only during the phase period of the half cycle of the power supply cycle. can do.

FIG. 10A is a diagram showing the configuration of the drive circuit in each of the embodiments shown in FIGS. 5 to 8. In the case of the configuration in which the output of the drive circuit is not controlled by the input voltage circuit to be output in the phase section of the half cycle on one side as in the embodiments of FIGS.
Although it is necessary to prohibit the drive output in the phase section from 360 degrees to 360 degrees, the circuit shown in FIG. 10A is necessary for such a case.

In FIG. 10A, the AC voltage from the AC power source 1 is rectified by the diode 41 as shown in FIG. 10B, and divided by the voltage dividing resistors 42 and 43. The voltage is compared with the reference voltage by the comparator 44, and
The phase detection signal as shown in (b) of (b) is output.

The phase detection signal from the comparator 44 is logically ANDed with the drive signal by the AND circuit 45, so that the PW as shown in FIG.
The M signal is output from the drive circuit 10 only in the phase section of 0 to 180 degrees of the power supply phase.

In the harmonic current reducing circuit of the present invention constructed as described above, the second harmonic current of the power supply current is about 40% of the fundamental current. 100V of equipment classified as Class A according to IEC standards and national guidelines
Since the limit value of the input second harmonic current is 2.48A, the fundamental current can flow about 6A. Therefore, the limit value can be satisfied up to about 600 W of equipment. Also, the limit value of the second harmonic current of 200V input is 1.2
Since it is 4 A, the fundamental current is about 3 when calculated in the same way.
A can be flowed, and the limit value can be satisfied up to about 600 W equipment. Even higher-order harmonic currents after the fourth order are generated, but they can be ignored because the ratio to the limit value is smaller than the second-order harmonic current. It should be noted that the odd-numbered harmonic currents sufficiently satisfy the limit value, and there is no problem.

Table 1 shows an example of measurement of the content rate of the harmonic current of the present invention with respect to the fundamental wave. Although Table 1 shows up to the 11th order, the content rate of the harmonic currents after the 12th order is 1% or less, and it is confirmed that there is no problem.

[0039]

[Table 1]

[0040]

As described above, according to the present invention of claim 1, the AC voltage from the AC power source is half-wave rectified by the rectifying diode, and the half-wave rectified voltage is switched by the switching means via the reactor. Switching and smoothing with an electrolytic capacitor via a high-speed recovery diode to supply to the load, drive based on the input voltage from the input voltage detection circuit, the input current from the input current detection circuit, and the output current from the output voltage detection means. Turn on / off the switching element so that the current from the AC power supply becomes a sine wave via the circuit.
Since it is off-driving and a half-wave rectifier circuit that uses one diode is used as the rectifier circuit, the number of parts can be reduced compared to the conventional full-wave rectifier circuit that uses four diodes. In addition to being economical, the number of diodes in the current loop can be reduced as compared with the conventional one, and the conversion efficiency can be improved. Of the even harmonics, the second harmonic generates about 40% of the fundamental wave,
Since the regulation value of the second harmonic is 2.48A, it is about 600
It is possible to satisfy the limit value of the harmonic current up to W devices.

According to the second aspect of the present invention, the AC voltage from the AC power source that has passed through the reactor is switched by the switching element via the protection diode, and the switched voltage is electrolyzed via the fast recovery diode. While smoothing with a capacitor and supplying it to the load, the AC voltage from the AC power supply is detected by the input voltage detection circuit via the diode and the resistor, the input current from the input current detection circuit, and the output voltage from the output voltage detection means. The switching element is turned on / off so that the current from the AC power supply becomes a sine wave via the drive circuit based on the output current, and since the half-wave rectification circuit is used, the number of parts can be reduced and the economy Can be achieved,
The number of diodes in the current loop is further reduced and the conversion efficiency can be further improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a harmonic current reduction circuit according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a detailed configuration of a harmonic current reduction control circuit used in the harmonic current reduction circuit shown in FIG.

3 is a diagram showing a power supply voltage waveform and a power supply current waveform in the harmonic current reduction circuit of FIG.

FIG. 4 is a waveform diagram showing an operation of the harmonic current reducing circuit shown in FIG.

FIG. 5 is a circuit diagram showing a configuration of a harmonic current reducing circuit according to another embodiment of the present invention.

FIG. 6 is a circuit diagram showing a configuration of a harmonic current reducing circuit according to still another embodiment of the present invention.

FIG. 7 is a circuit diagram showing a configuration of a harmonic current reduction circuit according to another embodiment of the present invention.

FIG. 8 is a circuit diagram showing a configuration of a harmonic current reducing circuit according to still another embodiment of the present invention.

9 is a diagram showing another configuration of the input voltage detection circuit in each of the embodiments shown in FIGS. 5 to 8 and a diagram showing operation waveforms.

FIG. 10 is a diagram showing a configuration of a drive circuit in each of the embodiments shown in FIGS. 5 to 8 and a diagram showing operation waveforms.

FIG. 11 is a diagram showing a configuration of a conventional harmonic current reduction circuit.

12 is a diagram showing operation waveforms of the conventional harmonic current reduction circuit of FIG.

[Explanation of symbols]

 1 AC power supply 2 Rectifier diode 3 Reactor 4a, 4b Voltage dividing resistor 5 Input voltage detection circuit 6 Current detection resistor 7 Input current detection circuit 8 High speed recovery diode 9 Switching element 10 Drive circuit 11 Output voltage detection circuit 12 Electrolytic capacitor

Claims (4)

[Claims] 1. A rectifier diode connected to one end of the AC power source for half-wave rectifying an AC voltage from the AC power source, a reactor connected in series to the rectifier diode, and a reactor connected in series to the reactor. A high speed recovery diode; an electrolytic capacitor connected in parallel to the load between the other end of the high speed recovery diode and the other end of the AC power supply; a switching element connected to the load side of the reactor; and the rectifying diode. A resistor connected between the load side of the AC power supply and the other end of the AC power supply, an input voltage detection circuit connected to the resistance for detecting an input voltage from the AC power supply, and detecting a current from the AC power supply. An input current detection circuit, a drive circuit that drives the switching element, an output voltage detection unit that detects a voltage across the electrolytic capacitor, and Based on the output signals from the input voltage detection circuit, the input current detection circuit, and the output voltage detection circuit, a signal for driving the switching element to turn on / off so that the current from the AC power supply becomes a sine wave is driven. A harmonic current reduction circuit comprising: a control circuit that supplies the circuit. 2. A reactor connected to one end of an AC power supply, a high speed recovery diode connected in series to the reactor, and a load parallel between the other end of the high speed recovery diode and the other end of the AC power supply. An electrolytic capacitor connected to the switching element, a switching element connected to the load side of the reactor, a protection diode connected in series to the switching element, a rectifying diode and a resistor connected in series to both ends of the AC power supply. An input voltage detection circuit connected to the resistor for detecting an input voltage from the AC power supply; an input current detection circuit for detecting a current from the AC power supply; a drive circuit for driving the switching element; Output voltage detection means for detecting the voltage across the capacitor, the input voltage detection circuit, the input current detection circuit, And a control circuit that supplies to the drive circuit a signal for driving the switching element on / off so that the current from the AC power supply becomes a sine wave based on the output signal from the output voltage detection circuit. Characteristic harmonic current reduction circuit. 3. The input voltage detection circuit, a photocoupler comprising a photodiode connected in series to the resistor and a phototransistor optically connected to the photodiode and outputting a phase detection signal, and the phase detection circuit. A counter that detects the difference between the time when the signal is at the high level and the time when the signal is at the low level, a shift register that is loaded with the count value of the counter and shifts the count value, and a count value of the counter and the shift register. 3. The harmonic current reducing circuit according to claim 2, further comprising a comparator that compares a register value and a zero-cross point of the AC power supply. 4. The drive circuit includes a comparator that generates a phase detection signal by comparing a half-wave rectified voltage of an AC voltage from an AC power source with a predetermined reference voltage, and a phase detection signal output from the comparator. 3. The harmonic current reduction circuit according to claim 2, further comprising an AND circuit that obtains a logical product with a drive signal.