JPH1056738A - Power factor improving rectifier circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent overshoot voltage appearing just after the power is turned on by means of a small-size load comprising only a few components by installing an overvoltage protective circuit for suppressing excessive rectified and smoothed voltage in parallel with a rectifying and smoothing capacitor. SOLUTION: An overvoltage protective circuit which is a serial combination of a resistor R1 and a varistor VDR, a surge absorbing element, in parallel with a rectifying and smoothing capacitor Ci. When a switch SW is closed and the power is turned on, for example, at a time t0 when a positive period of AC input voltage starts, AC input current during a period t0-t4 which is a first positive period of the AC input voltage becomes excessive rush current due to charging of the smoothing capacitor Ci. However, such conduction voltage as to prevent extreme overshoot voltage is selected for the varistor VDR and therefore overshoot voltage is absorbed by the varistor VDR and the current limiting resistor R1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a power factor improving rectifier circuit, and more particularly to a power factor improving rectifier circuit configured by inserting an AC reactor into an AC power supply input line.

[0002]

2. Description of the Related Art For example, in a power supply circuit, it is known to provide a power factor improving rectifier circuit in order to reduce power supply harmonic distortion generated by electronic equipment. For example, a choke input system in which a power choke coil as an AC reactor is inserted into an AC power input line is known as the power factor improving circuit. In this choke input method, the AC input current flows through the inductance of the power choke coil, thereby increasing the flow angle of the charging current to the smoothing capacitor, thereby improving the power factor.

FIG. 4 is a circuit diagram showing a power factor improving rectifier circuit using the choke input method.

In FIG. 1, reference numeral 1 denotes an AC power supply. One pole of the AC power supply 1 is connected to the winding 2a of the line filter transformer 2, and the other pole is a switch S.
It is connected to the winding 2b of the line filter transformer 2 via W.

[0005] SW indicates a switch for turning on / off the power supply circuit. Line filter transformer 2
CL inserted in the subsequent stage indicates an across capacitor, and forms a low-pass filter together with the line filter transformer 2. PCC indicates a power choke coil as an AC reactor. For example, PCC is inserted into one line of an AC input power supply as shown in FIG.
It may be inserted on the other pole line side.

Note that LN and RN indicate the inductance and the DC resistance of the power choke coil PCC, respectively, which will be described later.

3 is a diode D1, D2, D3
D4, which is a rectifier bridge circuit that performs full-wave rectification. As shown in the figure, a connection point of diodes D1 and D2 is used as an input terminal of one line of an AC power supply.
The connection point of D4 is the input terminal of the other pole line of the AC power supply, the rectification output terminal is the connection point of diodes D2 and D4, and the connection point of diodes D2 and D3 is connected to ground. Ci is a smoothing capacitor connected between the output terminal of the rectifying bridge circuit 3 and the ground, and smoothes the output that has been full-wave rectified by the rectifying bridge circuit 3 to obtain a rectified smoothed voltage Ei. Reference numeral 4 denotes a switching power supply circuit, which receives a rectified and smoothed voltage Ei as shown in the figure, converts it to, for example, required DC voltages E1 and E2, and outputs it.

In the power supply circuit having the above structure, a voltage Ei rectified and smoothed by the rectifying bridge circuit 3 and the smoothing capacitor Ci is obtained. At this time, the flow angle of the charging current is controlled by the action of the inductance LN of the power choke coil PCC. As a result, the power factor is improved. In this case, as an inductance LN, for example, when an attempt is made to improve the power factor to about 0.75, the input power is about 100 W, and LN = 10 mH or more at 100 V AC, and LN = 60 mH at 230 V AC.
It is said that it is above.

The above prior art is disclosed in, for example, P227 of the 10th edition of “Handbook of Practical Power Supply Circuit Design” by CQ Publishing Company.

[0010]

FIG. 5 shows an AC input voltage VAC, an AC input current IAC, and a rectified smoothing voltage EAC immediately after the switch SW is turned on in the power supply circuit shown in FIG.
The horizontal axis indicates the elapsed time since the switch SW was turned on, and the vertical axis indicates the voltage level and the current level, respectively. For example, as shown in FIG.
Assuming that the switch SW is turned on and the power is turned on at the timing of the start of the positive period of the AC input voltage VAC indicated as time 0, in this case, the AC input voltage V
During the period from t0 to t1 when AC is positive, the smoothing capacitor C
Due to the charging of i, the AC input current IAC becomes an excessive rush current as shown in the figure. The AC input current IAC during this period is determined by the DC resistance RN of the power choke coil PCC.
Is limited by the forward resistance of the diode in the rectifier bridge circuit 3. On the other hand, the rectified smoothed voltage Ei at this time is as follows.

That is, during this period, due to the action of the inductance LN of the power choke coil PCC, LN × IAC ×
The electromagnetic energy of IAC is accumulated, and this energy appears as a jump voltage VL shown in the figure and is superimposed on the AC input voltage VAC. As a result, the rectified smoothed voltage Ei at the time point t1 appears as an overshoot voltage extremely increased from a steady value as shown in the figure. And this t1
In the period from the time point to the time point t4, the rectified smoothed voltage Ei (potential of the smoothing capacitor Ci) becomes higher than the AC input voltage VAC due to overshoot as shown in the figure. As a result, a reverse voltage is applied to the diodes D2 and D4, so that the rectifier bridge circuit 3 cannot conduct, and the AC input current IAC does not flow as shown in the figure.

During this time, the rectified smoothed voltage Ei gradually decreases with the discharge of the smoothing capacitor Ci.
When the rectified and smoothed voltage Ei becomes lower than the AC input voltage VAC as shown in a period of 5, the AC input current IA
Flows out, and thereafter, a steady rectifying and smoothing operation is performed, and a rectified and smoothed voltage Ei corresponding to the AC input voltage VAC as shown in the figure.

As can be understood from the above description, in the power supply circuit having the power factor improving rectifier circuit having the circuit configuration as shown in FIG. 4, overshoot appears in the rectified smoothed voltage Ei at least when the power is turned on. . Therefore, for each diode and the smoothing capacitor Ci of the bridge rectifier circuit 3 to which such an overshoot voltage is applied, as well as components such as switching semiconductors, for example, those having an appropriate withstand voltage are selected. In addition, it is necessary to improve the withstand voltage of the power supply circuit, resulting in a problem that the cost is increased.

For example, taking each diode (D1 to D4) of the bridge rectifier circuit 3 as an example, if the overshoot voltage is about 140 to 150% of the rectified and smoothed voltage Ei in the steady state, 100V electronic equipment In the case of a power supply circuit corresponding to 200 V, it is necessary to improve the power supply circuit to have a withstand voltage of 200 V to 300 V, and for a power supply circuit corresponding to a 200 V electronic device, the power supply circuit is required to have a withstand voltage of about 400 V to 600 V.

[0015]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a power factor improving rectifier circuit capable of rectifying and smoothing an AC input voltage into which an AC reactor is inserted and outputting the rectified smoothed capacitor. In parallel, an overvoltage protection circuit for suppressing an excessive rectified and smoothed voltage is provided. For example, the overvoltage protection circuit is configured by connecting a resistor and a varistor in series.

[0016]

FIG. 1 is a circuit diagram showing an embodiment of a power factor improving rectifier circuit according to the present invention.
The same parts as those in FIG.

In this embodiment, as shown in the figure, an overvoltage protection circuit is provided in which a resistor R1 and a varistor VDR as a surge absorbing element are connected in series with a rectifying and smoothing capacitor.

Here, for example, the varistor VDR is selected to have a conduction voltage such that the jump-up voltage VL is not extremely generated during the period from t0 to t4 in FIG.

The surge withstand voltage of the varistor VDR and the rated power of the resistor R1 are as described above. Since the overvoltage protection circuit is designed to conduct only during the period from t0 to t4, for example, the AC power input is 50 Hz. Even in this case, since the period from t0 to t4 is a short time of about 40 ms, each of them requires a small capacity, and both can use small components.

FIG. 3 is a waveform diagram showing the operation of the power factor improving rectifier circuit of the present embodiment. As in FIG.
The operation waveforms of the AC input voltage VAC, the AC input current IAC, and the rectified smoothed voltage Ei immediately after W-on are shown, the elapsed time since the switch SW is turned on is shown on the horizontal axis, and the voltage level and current are shown on the vertical axis. Each level is indicated. For example, assuming that the switch SW is turned on and the power is turned on at time t0, which is the timing of the start of the positive period of the AC input voltage VAC, the alternating current during the period t0 to t4 when the AC input voltage VAC is first positive. Input current IAC
Causes an excessive rush current due to charging of the smoothing capacitor Ci as described above.

In this embodiment, the periods t0 to t4
In this case, since the varistor VDR is made conductive as described above, the jump voltage at this time is
5 and the current limiting resistor R1.
Does not appear.

As a result, in the period from t0 to t4, the rectified and smoothed voltage E having a substantially steady value in which overshoot is suppressed.
i is obtained, and thereafter, the steady value is maintained as shown in the figure.

In the case of this embodiment, unlike the case of FIG. 5, the rectified smoothed voltage Ei (the potential of the smoothing capacitor Ci) is close to the AC voltage Vac immediately after the switch is turned on.

FIG. 2 shows a main portion of another embodiment of the present invention, and other portions may be the same as those shown in FIG. In this case, as an overvoltage protection circuit, a snubber circuit including a capacitor C1 and a resistor R2 connected in series as shown in the figure is connected in parallel to the rectifying and smoothing capacitor.

With this configuration, the overshoot voltage can be suppressed in the same manner as in the previous embodiment, and the operation waveform immediately after the power is turned on can be substantially the same as that shown in FIG. 3, for example. You.

[0026]

As described above, in the power factor improving rectifier circuit of the present invention, the overvoltage protection circuit comprising a varistor connected in series and a resistor or a snubber circuit is provided in parallel with the rectifying and smoothing capacitor, so that the size and the size are reduced. By adding a small number of parts, it is possible to suppress an overshoot voltage generated immediately after turning on the power. Therefore, it is not necessary to improve the withstand voltage of the components of the constant voltage circuit such as the rectifying bridge circuit, the smoothing capacitor, and the subsequent switching power supply in consideration of the overshoot voltage as in the conventional case, so the cost is reduced accordingly. It has the effect of being done.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a power factor improving rectifier circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a main part of a power factor correction rectifier circuit according to another embodiment.

FIG. 3 is a waveform chart showing an operation of the power factor improving rectifier circuit in the embodiment.

FIG. 4 is a circuit diagram showing a power factor improving rectifier circuit in a conventional example.

FIG. 5 is a waveform chart showing an operation of the power factor improving rectifier circuit in the conventional example.

[Explanation of symbols]

1. AC power supply 2. Line filter transformer 3.
Rectifier bridge circuit, 4 ... switching power supply circuit, PCC
… Power choke coil, CL… Across capacitor,
Ci: smoothing capacitor, VDR: varistor, C1 ...
Capacitors, R1, R2 ... resistors.

Claims (2)

[Claims] 1. A power factor improving rectifier circuit for rectifying and smoothing an AC input voltage into which an AC reactor is inserted, and outputting the rectified smoothed voltage.
A power factor improving rectifier circuit, comprising: an overvoltage protection circuit for suppressing an excessive rectified smoothed voltage in parallel with the rectifying and smoothing capacitor. 2. The power factor improving rectifier circuit according to claim 1, wherein said overvoltage protection circuit comprises a resistor and a varistor connected in series.