JPH07222448A - Ac-dc converter - Google Patents

Abstract

PURPOSE:To simplify the circuit constitution of an AC-DC converter which uses a commercial AC power supply as an input source. CONSTITUTION:The AC-DC converter comprises a rectifying circuit 3 which receives an input AC voltage and which outputs a rectified voltage; a step-up converter having a choke coil 4 which receives the rectified voltage, a switching means 5 and a diode 6; a smoothing capacitor 7 which smoothes the output voltage of the step-up converter so as to be supplied to a load circuit 8; and a control circuit 15 having a current detection circuit 9, a voltage detection circuit 10 and a pulse-width control circuit 14. Then, the switching means 5 is turned on and off so as to limit the peak value of an input current to the step-up converter in order to stabilize the output voltage. Thereby, the output voltage is stabilized by a simple circuit constitution, the waveform of an input DC current becomes a trapezoidal wave shape, and a characteristic that a power factor is high and that a harmonic component is small can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses an AC power supply, particularly a commercial AC power supply as an input source, and is provided in, for example, an input circuit of a switching power supply unit and supplies an AC-D with a high power factor.
It relates to a C converter.

[0002]

2. Description of the Related Art In recent years, an AC-DC converter has been provided in an input circuit of various power supply circuits using a commercial AC power source as an input source for the purpose of shaping the input current waveform, thereby improving the power factor and increasing the harmonics contained in the input current. It has attracted attention as an active filter technology for reducing wave components.

A conventional AC-DC converter is shown in FIGS.
It is configured as shown in. In FIG. 5, 1 is an input AC power supply, 2 is an input filter, 3 is a full-wave rectifier circuit, 4,
Reference numerals 5 and 6 are a choke coil, a switching means, and a diode that form a boost converter. A smoothing capacitor 7 smoothes and supplies the output voltage of the boost converter to the load 8. Reference numeral 9 is a current detection circuit that detects the current of the switching means 5, 10 is an output voltage detection circuit that detects the voltage of the smoothing capacitor 7, 11 is a rectified voltage detection circuit that detects the rectified voltage of the full-wave rectification circuit 3, and 12 is an output. A multiplication circuit that multiplies the signals from the voltage detection circuit and the rectified voltage detection circuit to generate a reference signal, 13 turns on / off the switching means 5 at high frequency, and at the same time, outputs the current signal from the current detection circuit 9 and the reference from the multiplication circuit 12. It is a pulse width control circuit that receives a waveform and adjusts the on / off period of the switching means 5 so that the current signal follows the reference waveform.

This AC-DC converter operates as follows. The input AC voltage is full-wave rectified by the full-wave rectifier circuit 3. This rectified voltage is applied to the choke coil 4 when the switching means 5 is on, and a current flows from the full-wave rectifier circuit 3 through the choke coil 4 in the path of the switching means 5 to excite the choke coil 4. When the switching means 5 is off, the excitation energy of the choke coil 4 is released from the full-wave rectifier circuit 3 to the smoothing capacitor 7 via the diode 6.

In the multiplying circuit 12, the voltage of the smoothing capacitor 7 is detected by the output voltage detecting circuit 10, is compared with the reference voltage and is amplified, and the error signal is multiplied by the rectified voltage signal from the rectified voltage detecting circuit 11. Is performed, a reference waveform Vr [see (a) of FIG. 6] is generated at the output of the multiplication circuit 12 in proportion to the rectified voltage waveform and information of the output voltage is added. The control circuit 13 turns the switching means 5 on and off at a high frequency, compares the reference waveform Vr with the current signal Vi from the current detection circuit 9 [see (a) of FIG. 6], and when the current signal Vi reaches the reference waveform Vr. Switching means 5
To turn off. That is, the on / off period of the switching means 5 is adjusted so that the peak value of the current I1 flowing through the choke coil 4 (see (b) of FIG. 6) follows this reference waveform.

By the above operation, the input AC current Ii (see (c) of FIG. 6) is obtained by smoothing the current I1 flowing through the choke coil 4 by the input filter 2 while substantially stabilizing the output voltage. The input AC current Ii has a sinusoidal waveform proportional to the input AC voltage.

[0007]

The conventional configuration as described above has a problem that the detection circuits 10 and 11 and the multiplication circuit 12 for shaping the input current waveform are required, and the circuit scale becomes large. There is.

An object of the present invention is to provide an AC-DC converter which can simplify the circuit scale while improving the power factor and reducing the harmonic components, although the input AC current is not shaped into a sine wave. And

[0009]

An AC-DC converter of the present invention includes a rectifying circuit for receiving an input AC voltage and outputting a rectified voltage, a choke coil for receiving a rectified voltage of the rectifying circuit, a switching means, and a first means. Of a diode, a smoothing capacitor that smoothes the output voltage of the boost converter and supplies it to the load circuit, and limits the peak value of the input current to the boost converter in order to stabilize the output voltage of the boost converter. A control circuit for turning on / off the switching means is provided.

[0010]

With this configuration, the number of components is small, the current stress of the choke coil and the switching means is limited, the current stress is reduced, and the input AC current smoothed through the input filter is trapezoidal synchronized with the rectified voltage. A wavy waveform results in improved power factor and reduced harmonic components.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. The AC-DC converter of the present invention is configured as shown in FIG. 1, 1 is an input AC power supply, 2 is an input filter, 3 is a full-wave rectifier circuit, 4 is a choke coil,
Reference numeral 5 is a switching means and 6 is a diode. The choke coil 4, the switching means 5 and the diode 6 constitute a boost converter. A smoothing capacitor 7 smoothes and supplies the output voltage of the boost converter to the load 8.
9 is a current detection circuit that detects the current of the switching means 5 and outputs a current signal, 10 is a voltage detection circuit that detects the voltage of the smoothing capacitor 7 and compares it with a reference voltage, and outputs a voltage error signal, and 14 is the switching means 5 Is a pulse width control circuit that turns on and off at a high frequency, receives a current signal and a voltage error signal, and turns off the switching means 5 when the current signal reaches the voltage error signal. The current detection circuit 9, the voltage detection circuit 10 and the pulse width control circuit 14 form a control circuit 15.

FIG. 2 shows the waveform of the main part of the AC-DC converter. The input AC voltage is full-wave rectified by the full-wave rectifier circuit 3, and this rectified voltage Ei (see (a) of FIG. 2) is applied to the choke coil 4 when the switching means 5 is on, and the full-wave rectifier circuit 3 chokes the choke. Coil 4
A current flows through the path of the switching means 5 via the to excite the choke coil 4. When the switching means 5 is off, the excitation energy of the choke coil 4 is released from the full-wave rectifier circuit 3 to the smoothing capacitor 7 via the diode 6. The voltage detection circuit 10 has a response characteristic equal to or lower than the frequency of the input AC voltage, detects the voltage of the smoothing capacitor 7, compares and amplifies it with the reference voltage, and outputs the voltage error signal Ve. The voltage error signal Ve is a DC voltage as shown in (b) of FIG. 2, and the potential decreases when the output voltage rises due to the input / output conditions of the AC-DC converter, and conversely, when the output voltage falls, the potential drops. Behaves like rising. The current detection circuit 9 outputs a current signal Vi [see (b) of FIG. 2] according to the current waveform of the switching means 5. When the rectified voltage Ei is low and the current signal Vi is also small, the pulse width control circuit 14 drives the switching means 5 with a predetermined on / off ratio to excite the choke coil 4, but the current signal Vi.
Reaches the voltage error signal Ve, the ON period of the switching means 5 is limited so as not to exceed the voltage error signal Ve.
FIG. 2B shows the above operation. Therefore, the current I1 flowing in the choke coil 4 has a trapezoidal waveform as shown in FIG. 2C, and the AC input current Ii smoothed by the input filter 2 is shown in FIG.
It becomes a trapezoidal waveform as shown in.

As described above, according to the above embodiment, the input DC current Ii has a trapezoidal waveform while the output voltage is substantially stabilized without using the multiplying circuit 12 or the like which has been conventionally required, and a high power factor is achieved. Characteristic with few harmonic components can be obtained. Further, since the waveform becomes a trapezoidal wave having a lower peak value than that of a sine wave, current stress on the choke coil 4 and the switching means 5 can be reduced.

In the above-mentioned embodiment, the switching frequency of the switching means 5 may be sufficiently higher than the frequency of the input AC voltage, but harmonic components are reduced by the fixed ON period control rather than the fixed frequency. It The reason will be described below with reference to FIGS. 3 and 4.

First, in the case of a fixed frequency, the operation when the current signal Vi reaches the voltage error signal Ve is shown in FIG. When the current signal Vi reaches the voltage error signal Ve for the first time at the time T1, the switching means 5 which has been operating in the maximum ON period until then suddenly shortens the ON period, and the OFF period is extended accordingly. Therefore, the choke coil 4 is demagnetized more than necessary, and several switching cycles are required until the current signal Vi reaches the voltage error signal Ve, and the current signal Vi becomes the voltage error signal Ve at each switching cycle. This operation is repeated until it arrives [see (a) of FIG. 3]. Therefore, an oscillation waveform as shown in FIG. 3B is generated in the input current waveform Ii at the time corresponding to this portion, and the harmonic component is increased. On the other hand, in the case of the operation of fixing the off period, if the current signal Vi reaches the voltage error signal Ve for the first time at the time T1, the switching means 5 which has been operating in the maximum on period until then suddenly changes the on period. Although it is shortened, the off period is not extended, so the demagnetization amount of the choke coil 4 remains unchanged. As shown in (a) of FIG. 4, the transition from the maximum ON period state to the pulse width control state is relatively smooth, and the AC input current Ii does not have an oscillation waveform as shown in (b) of FIG. It is suppressed, and the harmonic components are reduced.

[0016]

As described above, according to the present invention, a rectifier circuit for receiving an input AC voltage and outputting a rectified voltage, a boost converter including a choke coil for receiving the rectified voltage, switching means and a diode, A smoothing capacitor that smoothes the output voltage of the boost converter and supplies it to a load circuit; and a control circuit that turns on and off the switching means so as to limit the peak value of the input current to the boost converter in order to stabilize the output voltage. Since the output voltage is stabilized, the input AC current can be made into a trapezoidal waveform with a high power factor and few harmonic components, and the current stress of the choke coil and switching means can be reduced. It is possible to realize a switching power supply device.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of an AC-DC converter of the present invention.

FIG. 2 is a main part waveform diagram of the embodiment.

FIG. 3 is a waveform diagram when the switching frequency is fixed.

FIG. 4 is a waveform diagram when a switching frequency is fixed in an off period.

FIG. 5 is a circuit configuration diagram of a conventional AC-DC converter.

FIG. 6 is an operation waveform diagram of a conventional AC-DC converter.

[Explanation of symbols]

 1 Input AC power supply 2 Input filter 3 Full wave rectification circuit 4 Choke coil 5 Switching means 6 Diode 7 Smoothing capacitor 8 Load 9 Current detection circuit 10 Voltage detection circuit 14 Pulse width control circuit 15 Control circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Haruo Watanabe 10-13 Minamimachi, Hanno City, Saitama Prefecture Shindengen Industrial Co., Ltd. (72) Inventor Yoshinori Kobayashi 10-13 Minamimachi, Hanno City, Saitama Prefecture Shinden Inside the factory of the former industrial stock company (72) Inventor Yutaka Sekine 10-13 Minami-machi, Hanno city, Saitama Shinden original factory

Claims (3)

[Claims] 1. A rectifier circuit that receives an input AC voltage and outputs a rectified voltage, a boost converter that includes a choke coil that receives the rectified voltage, switching means, and a diode, and an output voltage of the boost converter that is smoothed. AC-DC converter provided with a smoothing capacitor for supplying a load to a load and a control circuit for turning on / off the switching means so as to limit the peak value of the input current to the boost converter in order to stabilize the output voltage. 2. A control circuit, a current detection circuit for detecting a current of a choke coil or a switching means, a voltage detection circuit for detecting an output voltage of a boost converter and comparing it with a reference voltage to detect a voltage error, and a switching means. The AC-DC converter according to claim 1, comprising a pulse width control circuit for controlling the pulse width of the drive pulse signal for turning on and off the output by comparing the output of the current detection circuit and the output of the voltage detection circuit. 3. The AC-DC converter according to claim 2, wherein the pulse width control circuit is configured to control the ON period while keeping the OFF period of the switching means constant.