JP2000037072A - Power converting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power converting circuit capable of bringing power factor closer and closer to 1, suppressing the higher harmonic distortion of input power, and outputting stable DC voltage at the time of start-up or no-load. SOLUTION: A rectifier 2 outputs AC voltage whose input AC signal is full-wave rectified. A coil 3, a diode 4, a capacitor 5, and a MOSFET switch 7 convert the input AC power into output DC power to supply it to a DC load 6. A multiplier 21 attenuates for controlling an AC current similar signal obtained from an Ac current detecting circuit 20 based on the signal proportional to DC output obtained from a DC voltage detecting circuit 14. A comparing circuit 22 compares the attenuated and controlled AC current similar signal with the AC voltage similar signal obtained from an AC current detecting circuit 19, and its error output controls driving of a pulse width modulator 23. The pulse width modulator 23 outputs a duty pulse corresponding to the error output and controls the MOSFET switch 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power conversion circuit for converting AC input power to DC output power.

[0002]

2. Description of the Related Art FIG. 5 is a circuit block diagram showing a conventional step-up AC / DC converter. Between the output terminals (2a, 2b) of the rectifier 2 for inputting the AC signal 1 and the DC load 6
Between the terminals (6a, 6b) of the step-up coil 3
, The diode 4, the output capacitor 5 and the current shunt switch 7 constitute an AC / DC converter.

[0003] One output terminal 2a of the rectifier 2 and a DC load 6
The boosting coil 3 and the diode 4 are connected in series between the first terminal 6a and the first terminal 6a. A resistor 8 is connected between the other output terminal 2b of the rectifier 2 and the other terminal 6b of the DC load 6. The capacitor 5 is connected between the terminals (6a, 6b) of the DC load 6.

[0004] A connection point between the booster coil 3 and the diode 4;
A current shunt switch (MOSF) connected in series with the booster coil 3 between the connection point between the other terminal 6b of the DC load 6 and the resistor 8
(ET switch) 7 is provided.

A control mechanism including a pulse width modulator for controlling the conduction period of the MOSFET switch 7 is provided. The AC voltage detection circuit 9 is connected to one output terminal 2 of the rectifier 2.
The signal of a is input. The output of the AC voltage detection circuit 9 is supplied to one input of a multiplier 11.

The DC voltage detection circuit 14 inputs a signal at a DC output terminal 16 which is a connection point between the diode 4 and one terminal 6a of the DC load 6. The DC voltage detection circuit 14 is supplied with a reference voltage from a reference voltage generation circuit 15. Thereby, the DC voltage detection circuit 14 obtains a signal output proportional to the DC output obtained by comparing with the reference voltage. The output of the DC voltage detection circuit 14 is supplied to the other input of the multiplier 11.

[0007] The AC current detection circuit 10 inputs a signal at the other output terminal 2b of the rectifier 2. AC current detection circuit 10
And the output of the multiplier 11 become the respective inputs of the comparison circuit 12. The output of the comparison circuit 12 is input to the pulse width modulator 13. The output of the pulse width modulator 13 controls the gate of the MOSFET switch 7.

The pulse width modulator 13 provides the MOSFET switch 7 with a duty pulse corresponding to a difference signal between the output of the alternating current detection circuit 10 and the output of the multiplier 11 by the comparison circuit 12. The duty pulse is a pulse width control signal for continuously compensating for fluctuations in the input AC voltage and the DC load voltage in a constant cycle. With such a configuration, the control is performed so that the AC current waveform matches the AC voltage waveform.

[0009]

In the above configuration, the control signal for performing the pulse width control is proportional to the product of the input voltage of the AC voltage detection circuit 9 and the output voltage of the DC voltage detection circuit 14 ( Voltage squared characteristic). The input AC current is almost 0 at start-up and in no-load condition.
So, considering that input AC current cannot be detected,
In the case of the above configuration, the output voltage is determined by the output voltage itself. As a result, when the output voltage fluctuates at the time of start-up or the like and is in an unstable state, there is a problem that the unstable state is maintained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to reduce the power factor as close as possible to 1 and to suppress the harmonic distortion of the input current, as well as at the time of startup. Another object of the present invention is to provide a power conversion circuit capable of outputting a stable DC voltage even under no load conditions.

[0011]

According to the present invention, in a power conversion circuit for converting AC input power to DC output power applied to a DC load connected between load terminals, an input receiving AC input power, and A rectifier having an output for generating a wave-rectified AC voltage, a booster coil and a diode connected in series between the output of the rectifier and one of the load terminals, and a capacitor connected between the load terminals;
A switching circuit and a resistor connected in series with the boost coil between outputs of the rectifier; a current detection circuit for generating a first signal similar to a current flowing through the boost coil; and the full-wave rectified AC. A voltage detection circuit that generates a second signal similar to a voltage, a voltage detection circuit that generates a third signal similar to a DC voltage appearing at the load terminal,
A multiplier for generating a fourth signal corresponding to a product of the first signal and the third signal; and a fifth signal representing a difference between the second signal and the fourth signal. A comparison circuit; and a pulse width modulator for generating a sixth signal having a pulse width changed in accordance with the fifth signal, wherein the switching circuit operates during a period of the pulse width output by the sixth signal. It is characterized in that it is made conductive so that the waveform of the current flowing through the coil has the same shape as the waveform of the full-wave rectified AC voltage.

According to the present invention, the control signal for performing the pulse width control is proportional to the input voltage even when the input AC current is substantially zero and the input AC current cannot be detected at the time of start-up or no load. Voltage squared characteristic). In this case, the output voltage depends on the input voltage, and the output voltage has good stability.

[0013]

FIG. 1 is a circuit block diagram showing a step-up AC / DC converter according to a power conversion circuit of the present invention. Between the output terminals (2a, 2b) of the rectifier 2 to which the AC input 1 is input and the terminals (6a, 6b) of the DC load 6
Between the step-up coil 3, the diode 4,
The output capacitor 5 and the current shunt switch 7
/ DC converter.

One output terminal 2a of rectifier 2 and DC load 6
The boosting coil 3 and the diode 4 are connected in series between the first terminal 6a and the first terminal 6a. A resistor 8 is connected between the other output terminal 2b of the rectifier 2 and the other terminal 6b of the DC load 6. The capacitor 5 is connected between the terminals (6a, 6b) of the DC load 6.

A connection point between the step-up coil 3 and the diode 4;
A current shunt switch (MOSF) connected in series with the booster coil 3 between the connection point between the other terminal 6b of the DC load 6 and the resistor 8
(ET switch) 7 is provided.

A control mechanism including a pulse width modulator for controlling the conduction period of the MOSFET switch 7 is provided. The AC current detection circuit 20 inputs the signal of the other output terminal 2b of the rectifier 2. The output of the AC current detection circuit 20 is supplied to one input of a multiplier 21.

The DC voltage detection circuit 14 inputs a signal at a DC output terminal 16 which is a connection point between the diode 4 and one terminal 6a of the DC load 6. The DC voltage detection circuit 14 is supplied with a reference voltage from a reference voltage generation circuit 15. Thereby, the DC voltage detection circuit 14 obtains a signal output proportional to the DC output obtained by comparing with the reference voltage. The output of the DC voltage detection circuit 14 is supplied to the other input of the multiplier 21.

The AC voltage detection circuit 19 receives a signal at one output terminal 2a of the rectifier 2. AC voltage detection circuit 19
And the output of the multiplier 21 become the respective inputs of the comparison circuit 22. The output of the comparison circuit 22 is input to the pulse width modulator 23. The output of the pulse width modulator 23 controls the gate of the MOSFET switch 7.

The pulse width modulator 23 provides the MOSFET switch 7 with a duty pulse corresponding to a difference signal between the output of the AC voltage detection circuit 19 and the output of the multiplier 21 by the comparison circuit 22. The duty pulse is a pulse width control signal for continuously compensating for fluctuations in the input AC voltage and the DC load voltage in a constant cycle. With such a configuration, the control is performed so that the AC current waveform matches the AC voltage waveform.

In the present invention, the signal similar to the AC current obtained by the AC current detection circuit 20 is subjected to attenuation control by the multiplier 21 based on the signal proportional to the DC output obtained by the DC voltage detection circuit 14. The comparison circuit 22 compares the AC current similar signal subjected to the attenuation control with the AC voltage similar signal obtained by the AC voltage detection circuit 19. The error output obtained by the comparison circuit 22 controls the driving of the pulse width modulator 23. The pulse width modulator 23 outputs a pulse having a duty according to the error output. This pulse output is AC
/ Controls the MOSFET switch 7 of the DC converter.

The operation of the power conversion is as follows. MOS
When the FET switch 7 is turned on, energy proportional to the input voltage is stored in the booster coil 3, and when the switch 7 is turned off, the energy stored in the booster coil 3 is released to the output capacitor 5. This energy transfer action performs power transfer. When storing and releasing energy,
A circuit current of the same magnitude flows, which becomes an input alternating current.

That is, the input AC current flows through the resistor 8 connected to the terminal 2b of the rectifier 2. Therefore,
A waveform proportional to the input AC current is obtained at the end of the resistor 8 on the terminal 2b side. The waveform is taken out as a first signal by an AC current detection circuit 20, and is attenuated or amplified by a multiplier 21 to obtain an AC current similar waveform. obtain.

On the other hand, since a full-wave rectified AC voltage is generated between the output of the rectifier 2 and the booster coil 3, the AC voltage detection circuit 19 obtains a second signal having a waveform similar to the AC voltage.

The first signal having a waveform similar to the AC current obtained by the AC current detection circuit 20 is input to a multiplier 21. The multiplier 21 is controlled by an output signal (third signal) of the DC voltage detection circuit 14. The output of the multiplier 21 (fourth
) Is one input of the comparison circuit 22.

In the comparison circuit 22, the fourth waveform having a waveform similar to the AC current is output.
And a second signal having a waveform similar to the AC voltage to obtain a fifth signal. This fifth signal is applied to the pulse width modulator 23.
Control the voltage signal. The voltage signal (sixth signal) of the pulse width modulator 23 becomes a duty pulse that changes at a constant frequency, and controls on / off of the MOSFET switch 7.

Therefore, the MO signal is set so that the fourth signal having the similar waveform to the AC current and the second signal having the similar waveform to the AC voltage coincide with each other.
Since the ON / OFF of the SFET switch 7 is controlled, the AC input current becomes similar to the AC input voltage, and the power factor approaches 1 infinitely. This reduces the harmonic current. At the same time, the DC output is controlled so as to have a value proportional to the reference voltage, so that a stable DC voltage is obtained.

Since the voltage signal (sixth signal) of the pulse width modulator 23 is a chopping control signal for AC input to the smoothing capacitor 5 for the purpose of power factor improvement, the constant frequency is Of course, it is higher than the frequency of the AC input 1.

In some cases, it is preferable that the voltage signal (sixth signal) of the pulse width modulator 23 be synchronized with a constant frequency signal from the outside. For example, when a power supply waveform is displayed on a monitor, the horizontal scanning frequency and the voltage signal of the pulse width modulator 23 are synchronized. As a result, switching noise in the MOSFET switch 7 can be inserted during the blanking period of horizontal scanning, and the display is not disturbed by the influence of the switching noise.

FIG. 2 is a circuit block diagram showing a configuration according to a second embodiment of the present invention, and shows a modification of FIG. 1 in that the input of the AC voltage detection circuit 20 is connected between the inputs of the rectifier 2.
Other configurations are the same as those in FIG.

With the above configuration, the same operation as that of the configuration of FIG. 1 can be realized, and the same effect as that of the configuration of FIG. 1 can be obtained. In the above two embodiments, the multiplier 21 mainly shows the damping action. However, when the input AC voltage is small, an amplifying operation is also possible.

According to the configuration of each of the above embodiments, the DC output voltage is detected, and the first signal from which the input AC current is detected is attenuated or amplified in accordance with the third signal obtained by comparison with the reference voltage. To obtain a fourth signal similar to the input AC current waveform. A second signal similar to the fourth signal and the input AC voltage waveform
To obtain a fifth signal as an error output. A sixth signal for controlling the pulse width to the converter section is generated by the fifth signal. The shunt switch is switched by the sixth signal that has become the duty control pulse, and the input AC current works so as to be similar to the input AC voltage, thereby bringing the power factor of the input power as close to 1 as possible and reducing the input harmonic current. I do.

Further, according to the present invention, at start-up or in a no-load state, even if the input AC current is almost zero and the input AC current cannot be detected, the control signal for performing the pulse width control is proportional to the input voltage. (Square characteristic of voltage). In this case, the output voltage depends on the input voltage, and the output voltage has good stability.

That is, in the conventional technique having the configuration shown in FIG.
As shown in FIG. 4, assuming that the voltage system input to the multiplier 11 is x and z and the current system to the comparison circuit 12 is y, Vo = K (z · ax + by) (1) Can be expressed as

Since the load current is zero when starting or during no load, if the current y = 0 in the above equation (1), the following equation is obtained: Vo = K · z · ax (2) The voltage becomes a square characteristic of the voltage determined by the product of the input voltage and the output voltage, and the circuit becomes unstable. At the time of start-up, it is necessary to take measures such as waiting for the operation to stabilize or connecting a dummy load. is there.

On the other hand, FIG.
In FIG. 2 and FIG. 2, as shown in FIG. 3, the DC output Vo is based on the current system y and the voltage system z input to the multiplier 21,
Since the voltage system x becomes 2, Vo = K (z · ay + bx) (3)

Considering the start-up time and no load, the load current is zero. Therefore, in the above equation (3), if the current y = 0, then Vo = K · bx (4), and the output voltage becomes It depends only on the input voltage (square characteristic of voltage). That is, according to the circuit configuration of the present invention, the function of the circuit is simple and the stability is excellent under the conditions at the time of startup and no load. This eliminates the need for the above-described conventional measures at the time of startup and no load.

As described above, according to the present invention, the input AC current is made to be equal to the input AC voltage at startup or in a no-load state even if the input AC current is almost zero and the input AC current cannot be detected. The control signal for performing the pulse width control for performing the control is proportional to the input voltage. Therefore, the output voltage depends on the input voltage, and the output voltage is excellent in stability.

[0038]

As described above, according to the present invention, a stable DC voltage output is possible even under conditions of start-up and no load, and harmonic distortion of input current is suppressed, and power factor is reduced. Can be provided as close to 1 as possible.

[Brief description of the drawings]

FIG. 1 shows a step-up AC / AC according to a first embodiment of the present invention.
FIG. 2 is a circuit block diagram illustrating a DC converter.

FIG. 2 is a circuit block diagram showing a second embodiment of the present invention, showing a modification of the configuration of FIG. 1;

FIG. 3 is a conceptual block diagram relating to a control operation for explaining one of the effects of the present invention.

4 is a conceptual block diagram related to the control operation of the related art in FIG. 5 for explaining in comparison with FIG. 3;

FIG. 5 is a circuit block diagram showing a conventional step-up AC / DC converter.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 AC input 2 rectifier 3 step-up coil 4 diode 5 output capacitor 6 DC load 7 current shunt switch (MOSFET switch) 8 resistor 14 DC voltage detection circuit 15 reference voltage generation circuit 16 DC Output terminal 19: AC voltage detection circuit 20: AC current detection circuit 21: Multiplier 22: Comparison circuit 23: Pulse width modulator

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Toshimitsu Okada 3-3-9, Shimbashi, Minato-ku, Tokyo Toshiba Abu E Co., Ltd. F-term (reference) 5H006 AA02 CA02 CA07 CB01 CB03 CC02 CC08 DA02 DA04 DC02 DC05 5H730 AA18 BB14 BB57 CC04 DD04 FD01 FD11 FD41 FG05

Claims (3)

[Claims] 1. A power conversion circuit applied to a DC load connected between load terminals and converting AC input power to DC output power, wherein an input receiving the AC input power and an AC voltage subjected to full-wave rectification are generated. A rectifier having an output, a booster coil and a diode connected in series between the output of the rectifier and one of the load terminals, a capacitor connected between the load terminals, and the output of the rectifier. A switching circuit and a resistor connected in series with the boosting coil; a current detection circuit for generating a first signal similar to a current flowing through the boosting coil; a second signal similar to the full-wave rectified AC voltage A voltage detection circuit that generates a third signal similar to the DC voltage appearing at the load terminal; and a voltage detection circuit that corresponds to a product of the first signal and the third signal. A multiplier that generates a fourth signal; a comparison circuit that generates a fifth signal representing a difference between the second signal and the fourth signal; and a pulse width that changes according to the fifth signal And a pulse width modulator that generates a sixth signal. The switching circuit is turned on during a pulse width output by the sixth signal, and a current waveform flowing through the coil is subjected to the full-wave rectification. A power conversion circuit characterized by having the same shape as the waveform of an AC voltage. 2. The power conversion circuit according to claim 1, wherein the multiplier amplifies or attenuates the first signal according to the third signal, and outputs a fourth signal. . 3. The frequency of the sixth signal having a pulse width output is synchronized with a constant frequency signal from the outside, and the frequency exceeds the frequency of the AC input power. 2. The power conversion circuit according to 1.