JPH08149797A - Low voltage output active filter - Google Patents

Abstract

PURPOSE: To obtain a low voltage active filter which can suppress harmonic currents. CONSTITUTION: An AC input voltage Vin is full-wave rectified through a diode bridge D1 to produce a pulsation input voltage Va, which is then passed through a step-down switching circuit D, a step-up active filter B, and a smoothing circuit comprising a step-up/rectification diode D2 and a smoothing capacitor C1 to produce a DC output voltage Vo. When an input voltage detection circuit U3 detects an input voltage Va lower than an output voltage Vo, the step-up circuit B is operated through a control circuit U1 to stabilize the output voltage Vo. When the input voltage Va is higher than the output voltage Vo, the step- down circuit D is operated through a control circuit U2 to stabilize the output voltage Vo and to approximate the input current Iin to a sine wave.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active filter for suppressing harmonic current in a stabilized power supply device.

[0002]

2. Description of the Related Art Conventionally, a configuration example shown in FIG. 3 is known as an apparatus of this type. In the figure, A is a rectifying circuit, B is a boosting active filter, C is a smoothing circuit, D1 is a diode bridge for rectifying an AC input voltage, Q1 is a switching transistor, L1 is a boosting inductor, and D2 is A boosting diode, C1 is an output smoothing capacitor, R1 is an overcurrent detecting resistor, and U1 is a control circuit for driving the switching transistor Q1. Note that Vin is an AC input voltage, Va is a pulsating input voltage obtained by rectifying an AC input, Iin is an input current, and Vo is a DC output voltage.

According to the constant voltage power supply device having the above structure, the control circuit U1 monitors the output voltage Vo and the input voltage Va while the output voltage Vo is constant and the AC input current Iin becomes a sine wave. Control the drive pulse width. The input effective voltage Va is accumulated in the boosting inductor L1 by driving the switching transistor Q1, and the energy accumulated when the switching transistor Q1 is stopped is added to the input voltage Va and supplied to the capacitor C1 through the diode D2. To do. In addition, the resistor R1 detects the current at the time of switching of the switching transistor Q1 and serves as an overcurrent protection function, and the output voltage Vo is boosted to a voltage of 1.1 to 1.3 times the peak value of Va. The input voltage Vin comes to approximate a sine wave, and the harmonic current can be suppressed.

[0004]

However, since the active filter having the above-mentioned configuration is a booster circuit, the output voltage becomes a high voltage, and the converter connected to this circuit needs to have a high withstand voltage input. It was

In order to solve the above problems, the present invention provides
An object of the present invention is to provide an active filter circuit capable of setting a low DC output voltage of a constant voltage power supply device.

[0006]

In order to achieve the above object, the present invention incorporates a step-down switching circuit in a conventional circuit (shown in FIG. 3) and sets an input voltage detected by an input voltage detection circuit. The boosting active filter is operated while the voltage is lower than the input voltage, and the step-down switching circuit is operated when the input voltage is high to set the output voltage low, and the input current is approximated to a sine wave.

[0007]

In the low-voltage active filter used in the constant voltage power supply device of the present invention, the input voltage is set while monitoring the change in the voltage detected by the input voltage detection circuit by the first or second switching transistor, that is, the output voltage. The boost active filter operates while the voltage is lower than the specified voltage, and the step-down switching circuit operates when the input voltage is high, so that the output voltage can be set low and the input current can be approximated to a sine wave. It becomes possible to stabilize the output voltage.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of the present invention.
FIG. 2 shows a waveform diagram of a main part of FIG. In FIG. 1, the same parts as those in FIG. 3 are denoted by the same reference numerals, D is a step-down switching circuit newly incorporated in a conventional circuit, Q2 is a switching transistor, D3 is a flywheel diode, and U1 is a switching transistor. A first control circuit for driving Q1, a second control circuit for driving a switching transistor Q2, U2, and a set reference voltage Vb for U3.
An input voltage detection circuit for detecting whether the input voltage Va is higher or lower than the first control circuit U1 when the detected voltage is lower than Vb.
If the detected voltage is higher than Vb, the second control circuit U2 is activated.

The operation of the present invention having the above configuration will be described with reference to FIGS.
To explain. When the input voltage Va is lower than the set reference voltage Vb, the switching transistor Q2 is in a driving state and operates as a booster circuit similar to the active filter B. However, when the input voltage Va rises and exceeds the reference voltage Vb, the control circuit U1 is stopped and the switching transistor Q1 driven by this circuit U1 is stopped (see FIG. 2 (c)). Input voltage Va
2 rises above the reference voltage Vb, the second control circuit U2 is driven by the input voltage detection circuit U3,
The operation starts as shown in (b), and the power is supplied to the smoothing capacitor C1 while stepping down, so that the input current Iin
Continuously flows, and has a waveform approximate to a sine wave as shown in FIG. Therefore, it becomes possible to set the output voltage Vo low by setting Vb lower than the peak value of Va.

[0010]

As described above, according to the present invention,
The following effects are achieved. Since the step-down switching circuit is incorporated in the conventional active filter,
The circuit configuration of the active filter that can set the output voltage low becomes possible, and the circuit components such as the switching element, the output rectifier diode, and the output rectifier capacitor can use the low withstand voltage components. A converter with a low input voltage can be used as the converter.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

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

FIG. 3 is a circuit diagram showing a conventional example.

[Explanation of symbols]

 A rectifier circuit B step-up active filter C smoothing circuit D step-down switching circuit D2 step-up rectifier diode D3 flywheel diode L1 step-up inductor C1 output smoothing capacitor U1, U2 control circuit U3 input voltage detection circuit Q1, Q2 switching transistor Vin AC Input voltage Iin Input current Va Input voltage Vo DC output voltage Vb Setting reference voltage

Claims (1)

[Claims] 1. An active filter for suppressing a harmonic current in a stabilized power supply device, which is connected between a rectifying circuit for inputting an AC power supply and rectifying it and a smoothing circuit, A step-down switching circuit connected to the output terminal pair of the rectifier circuit and a step-up active filter connected to the switching circuit, wherein the step-down switching circuit has a second collector connected to one of the output terminal pair of the rectifier circuit. Switching transistor of
A second control circuit for driving and controlling an overcurrent detection resistor connected to the other of the pair of output terminals, a diode connected between the emitter of the second switching transistor and the resistor, and a base of the switching transistor. And a step-up active filter having a step-up inductor connected in series with an emitter of the second switching transistor, and a first switching step connected in parallel with the step-up inductor and a diode of the step-down switching circuit. A first control circuit for driving and controlling a base of the first switching transistor, and further, an input voltage detection circuit for detecting an output voltage of the rectifier circuit is provided to detect a high or low level of the input voltage. Then first
An active filter for low voltage, characterized in that either one of the second control circuit and the second control circuit is driven and the other is stopped.