JPH01148072A - 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 second control means DC-DC converter equal to a reference voltage. 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 a switching element Q1 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 shorter the ON-time of said switching element Q1 is made. Therefore, the current waveform coincides with the voltage waveform. Also, the ON-time of the switching element Q1 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. In other words, the AC input is rectified by the rectifier circuit 1 made up of a diode bridge, and the pulsating current is smoothed by the capacitor 2 and input to the 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 If 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. This pulsed current is synchronized with the waveform of the power supply, so if many switching regulators are connected to a commercial power supply, their respective pulsed currents will be superimposed, making the problem even worse.

Also, 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 terminal 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 is compatible with both a 100 V power source and a 200 V 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 so that changes in the input voltage can be handled by switching the transformer's output and output. In any case, with conventional equipment,
It was necessary to perform a switching operation according to the voltage rank of the AC power supply 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; a switching element, an inductor connected in series with the switching element between the output of the rectifier circuit, and a diode and a capacitor connected in series across the inductor so that current flows through the inductor when the switching element is off. a chopper circuit that obtains a smoothed DC output of opposite polarity to the input from both ends of the capacitor; an isolated DC-DC converter that stabilizes the output of the chopper circuit and obtains a DC output of a predetermined voltage; and the rectifier A first step that detects the waveform of the output voltage of the circuit and the waveform of the low frequency component of the current flowing through the inductor, and controls the driving pulse width of the switching element so that the current waveform changes in accordance with the voltage waveform. and a second control means for detecting the output voltage of the DC-DC converter and controlling the drive pulse width of the switching element so as to reduce the error of the output voltage with respect to the reference voltage. It is something.

(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) Switching element Q driven on/off at a frequency sufficiently higher than the AC power supply by the circuit 31
1, an inductor L1 connected in series between the output of the rectifier circuit 10 together with the switching element Q1, and a diode D1 and a capacitor C1 connected in series across the inductor L1 so that current flows through the inductor L1 when the switching element Q1 is off. and has. Capacitor C1
has a fairly large capacitance, and a smoothed and voltage stabilized (described later) DC output with the opposite polarity to the input is taken out from both ends of this. 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 changes the drive pulse width (on time) of the switching element Q1 so that the differential output is minimized. Also, DC-
The error of the output voltage V3 of the DC converter 40 with respect to the reference voltage Vs is detected by the error amplifier 35, and this output becomes the control voltage of the vCA 32 via the 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 changes the on-time of the switching element Q1.

When the switching element Q1 is on, current flows from the rectifier circuit 10 to the inductor L1 through the switching element Q1, 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. When the switching element Q1 is turned off, a current due to the release of the energy stored therein is supplied to the capacitor C1 side.

The pulse width control based on the comparison between the input voltage waveform and the current waveform of the inductor L1 works to shorten the on-time of the switching element Q1 as the input voltage V1 increases. Through this control, the change in the current waveform becomes approximately 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 on time of the switching element Q1 will be shortened, and if the output voltage v3 is too low, the on time will be extended. is increased or decreased, and as a result, the DC-DC converter 4
It acts to bring the zero output voltage V3 closer to the reference voltage Vs.

(Effects of the Invention) As described in detail above, in the power supply device according to the present invention, the input terminal changes almost following the AC input voltage, becomes almost a sine wave with no phase difference, and is 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.

In addition, the boosting and bucking effects of the chopper circuit and the second
Due to the feedback control action of the output voltage by the control means, the output voltage can be kept constant even when the AC input voltage fluctuates or the voltage rank is changed. As a result, no switching is required,
For example, a power supply device that is compatible with AC 100V power supplies to AC 400V power supplies can be easily constructed.

[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. FIG. 4 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 - Iro Ken Axial Patent Attorney Matsu
Masatoshi Moto Figure 2, Figure N3, Figure 4

Claims (1)

[Claims] (1) A rectifier circuit that full-wave rectifies the AC power source to obtain a pulsating output; A switching element that is driven on/off at a sufficiently higher frequency than the AC power source, and a connection between the output of the rectifier circuit together with this switching element. It includes an inductor connected in series, and a diode and a capacitor connected in series across the inductor so that current flows through the inductor when the switching element is turned off, and a smoothed capacitor with a polarity opposite to that of the input is connected from both ends of the capacitor. a chopper circuit that obtains a DC output; an isolated DC-DC converter that stabilizes the output of the chopper circuit and obtains a DC output of a predetermined voltage; a waveform of the output voltage of the rectifier circuit and a low current flowing through the inductor; a first control means for controlling the drive pulse width of the switching element so that the current waveform changes in accordance with the voltage waveform; detecting the output voltage of the DC-DC converter; and second control means for controlling the drive pulse width of the switching element so as to reduce the error of the voltage with respect to the reference voltage.