JPH01148074A - Power unit - Google Patents

Abstract

PURPOSE:To reduce noise and to keep an output voltage constant by changing an inductor current waveform through a first control means in such a manner that the waveform follows a voltage waveform and by making the output voltage of a DC-DC converter equal to a reference voltage through a second control means. CONSTITUTION:In a differential amplifier 33, the waveform of an input V1 of a chopper circuit 20 is compared with the waveform of an electric current I1 of an inductor L1, and the ON-time of switching elements Q1, Q2 is changed by a PWM circuit 31 so that a current waveform follows a voltage waveform. At the ON-time, energy is accumulated in the inductor L1, and at the OFF-time, an electric current is supplied to a capacitor C1. In the pulse width control, the higher an input voltage V1, the ON-time of the switching elements Q1, Q2 is made. Therefore, the current waveform coincides with the voltage waveform. The ON-time of the switching elements Q1, Q2 is shortened when an output voltage V3 is too high, and lengthened when the voltage is too low. Thus, the input voltage V2 of a DC-DC converter 40 is increased or decreased so that the output voltage V3 approaches a reference voltage VS.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a switching power supply device that generates DC power from AC power.

(Prior Art) Most common switching power supplies that take commercial power as an input use a capacitor input type rectifier circuit as shown in FIG. That is, an AC input is full-wave rectified by a rectifier circuit 1 consisting of a diode bridge, and its pulsating current is smoothed by a capacitor 2 and input to a DC-DC converter 3. As is well known, the waveforms of each part of this capacitor input type rectifier circuit are as shown in FIG.

(Problems to be solved by the invention) For example, “Switching regulator design know-how J
(CQ Publishing Co., Ltd., August 1, 1986, author: Yoyoaki Hase), pages 170-171, in a capacitor input type rectifier circuit, the input current Ii is the AC input A pulse current flows for a very short time every half cycle, and the current peak value becomes extremely large.

Therefore, circuit elements (elements such as rectifier diodes and inrush prevention circuits) where the input current flows must have sufficient current resistance, and this is one of the factors hindering cost reduction. ing.

Furthermore, sharp pulse currents with large peak values flow through the AC power supply line, which considerably worsens the noise environment. Since this pulsed current is synchronized with the waveform of the power supply, if a large number of switching regulators are connected to a commercial power supply, their respective pulsed currents will be superimposed, making the problem even worse.

In addition, in the case of a capacitor input type rectifier circuit, if the AC input voltage is changed from 100V to 200V, for example,
Since the output voltage of the smoothing capacitor 2 changes in the same way, the input voltage to the DC-DC converter 3 will exceed the permissible range and will not operate as a stabilized power supply. In a conventional device that can accept both a 100V power source and a 200V power source as an input, the configuration of the rectifier section is changed over between a voltage doubler rectifier circuit and a normal full-wave rectifier circuit using a switch. By switching the switch according to the voltage rank of the input power source, a smoothed voltage within an allowable range can be supplied to the DC-DC converter. In another conventional device, a transformer is provided at the input stage, and the input voltage can be changed by changing the taps of the transformer. In any case, conventional devices require switching operations depending on the voltage rank of the AC power source used.

This invention was made in view of the above-mentioned conventional problems, and its purpose is to make the input current from the AC power supply almost proportional to the input voltage, similar to the case of a resistive load, and to increase the voltage rank of the AC power supply. To provide a power supply device capable of generating a substantially constant voltage across a capacitor even if the voltage is changed significantly.

(Means for Solving the Problems) A power supply device according to the present invention includes a rectifier circuit that full-wave rectifies an AC power source to obtain a pulsating output; an inductor sandwiched between the switching elements and connected in series between the outputs of the rectifying circuit; and an inductor connected in series across the inductors so that current flows through the inductors when the switching elements are off. A chopper circuit includes two diodes and a capacitor, and one end of the input and output is connected in common so as to obtain a smoothed DC output of the same polarity as the input from both ends of the capacitor; the output of the chopper circuit is stabilized. an isolated DC-DC converter that obtains a DC output of a predetermined voltage; detects the waveform of the output voltage of the rectifier circuit and the waveform of the low frequency component of the current flowing through the inductor, and the current waveform follows the voltage waveform; a first control means for controlling the drive pulse width of the switching element so as to change the width; detecting the output voltage of the DC-DC converter; A second control means for controlling the driving pulse width of the element; and;

(Function) In the above configuration, the driving pulse width of the switching element is controlled by the first control means, and the current flowing through the inductor changes substantially following the full-wave rectified voltage waveform. Further, the driving pulse width of the switching element is controlled by the second control means, so that the output voltage of the DC-DC converter is maintained approximately equal to the reference voltage.

(Embodiment) FIG. 1 shows the configuration of a power supply device according to an embodiment of the present invention, and FIG. 2 is a waveform diagram of its main parts.

The sine wave AC input is full-wave rectified by a rectifier circuit 10 consisting of a diode bridge, and is input to a step-up chopper circuit 20, which will be described in detail below. The chopper circuit 20 is a PWM
(Pulse width control) Connected in series between two switching elements Q1 and Q2, which are driven on and off simultaneously by a circuit 31 at a sufficiently higher frequency than the AC power supply, and the output of the rectifier circuit 10, which is sandwiched between switching elements Q1 and Q2. two diodes D1 connected in series across the inductor L1 so that current flows through the inductor L1 when the switching elements Ql and Q2 are off.
and D2 and a capacitor C1. One end of this capacitor C1 is commonly connected to the negative input line. The capacitor C1 has a considerably large capacity, and a DC output that has been smoothed and voltage stabilized (described later) is taken out from both ends of the capacitor C1. Note that the capacitor C2 is a small capacitor for absorbing high frequency ripples, and is not essential to the present invention.

The output of the chopper circuit 20 is further stabilized by an isolated DC-DC converter 40 to a predetermined voltage output, which is supplied to the load.

The DC-DC converter 40 in this example has a well-known configuration, including the primary winding L2 of the transformer 41 and the switching element Q.
3 are connected in series to both ends of the capacitor C1, and the switching element Q3 is driven on/off by the drive circuit 42 at a sufficiently high frequency and with a predetermined duty ratio. Then, the output of the secondary winding L3 of the transformer 41 is rectified and smoothed by diodes D3 and D4, an inductor L4, and a capacitor C3 to obtain a DC output.

The signal of the output voltage V1 of the rectifier circuit 10 afterward rectification is VCA
The signal is input to a differential amplifier 33 via a (voltage controlled variable gain amplifier) 32. Inductor L1 of chopper circuit 20
Current 11 flowing through is detected by current transformer 34, and its low frequency component signal is input to differential amplifier 33. The PWM circuit 31 operates according to the differential output of the differential amplifier 33, and switches the switching elements Ql,
Change the drive pulse width (on time) of Q2. Also,
Reference voltage V of output voltage V3 of DC-DC converter 40
An error with respect to s is detected by an error amplifier 35, and its output becomes a control voltage for the VCA 32 via a photo-isolator 36.

In the above configuration, in the differential amplifier 33, the waveform of the input v1 of the chopper circuit 20 and the waveform of the current 11 flowing through the inductor L1 are compared, and the PWM circuit 31, the switching element Q1. Q2 on time can be changed.

When switching elements Ql and Q2 are on, rectifier circuit 1
Current flows from 0 to the inductor L1 through the switching elements Ql and Q2, and energy is stored in the inductor L1. The current increase value during this on-period is proportional to the input voltage v1 and proportional to the on-time. Switching element Q1. When Q2 is turned off, a current due to the release of the energy stored in Q2 is supplied to the capacitor C1 side.

Pulse width control by comparing the input voltage waveform and the current waveform of the inductor L1 results in that the larger the input voltage V1 is, the more the switching element Q1. It acts to shorten the on time of Q2. This control changes the current waveform by
Almost equal to the full-wave rectified waveform of the input voltage. In other words, when viewed from the AC input side, the input voltage and input current have almost the same waveform and there is no phase difference, resulting in almost the same state as if the load were a resistor. The above is the operation of the first control means described above.

Further, the second control means operates as follows.

The larger the output voltage v3 is than the reference voltage Vs, the more the VCA32
The smaller the gain is, and the smaller v3 is than Vs, the more VC
The gain of A32 increases. This VCA 32 is a circuit through which the waveform signal of the input voltage in the first control means passes, and its gain becomes a basic parameter of the first control means. In other words, if the output voltage v3 is too high, the switching element Ql.

The on-time of Q2 is shortened, and on the other hand, if it is too low, the on-time is extended, thereby reducing the output voltage v3 of the chopper circuit 20, that is, the input voltage v of the DC-DC converter 40.
2 is increased or decreased, and as a result, it acts to bring the output voltage v3 of the DC-DC converter 40 closer to the reference voltage Vs.

(Effects of the Invention) As explained in detail above, in the power supply device according to the present invention, the input current changes almost following the AC input voltage, becomes almost a sine wave with no phase difference, and when viewed from the AC power supply side. The relationship between voltage and current is almost the same as in the case of a resistive load. Therefore, unlike conventional capacitor input type rectifier circuits, large pulse currents do not flow intensively in a short period of time, and restrictions on the current withstand characteristics of circuit elements are relaxed, and various It is possible to reduce harmful noise.

Further, the output voltage can be kept constant even when the AC input voltage fluctuates or the voltage rank is changed by the step-up and step-down actions of the chopper circuit and the feedback control action of the output voltage by the second control means. can be kept. As a result, it becomes possible to easily construct a power supply device that does not require any switching and is compatible with, for example, an AC 100V power source to an AC 400V power source.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a power supply device according to an embodiment of the present invention, FIG. 2 is a waveform diagram of essential parts of the circuit of FIG. 1, FIG. 3 is a circuit diagram of a conventional capacitor input type power supply device, and FIG. The figure is a waveform diagram of essential parts of the circuit of FIG. 3. 10... Rectifier circuit 20... Chopper circuit 31... Pulse width control circuit 40... DC-DC converter patent applicant
Representative of Fuji Electrochemical Co., Ltd.
Patent Attorney - Ken Iro Rinma Patent Attorney Matsu
Masatoshi MotoFigure 2Figure 3Figure 4

Claims (1)

[Claims] (1) A rectifier circuit that full-wave rectifies the AC power source to obtain a pulsating output; Two switching elements that are driven on and off simultaneously at a sufficiently higher frequency than the AC power source; An inductor is connected in series between the outputs of the rectifier circuit, and two diodes and a capacitor are connected in series across the inductor so that current flows through the inductor when the switching element is turned off. A chopper circuit in which one end of the input and output is commonly connected to obtain a smoothed DC output with the same polarity as the input; and an isolated DC-DC converter that stabilizes the output of the chopper circuit to obtain a DC output of a predetermined voltage. ; Detecting the waveform of the output voltage of the rectifier circuit and the waveform of the low frequency component of the current flowing through the inductor, and controlling the drive pulse width of the switching element so that the current waveform changes to follow the voltage waveform. a first control means for detecting the output voltage of the DC-DC converter, and a second control means for controlling the drive pulse width of the switching element so as to reduce an error of the output voltage with respect to a reference voltage; A power supply device characterized by: