JPH01152956A - Power unit - Google Patents

Abstract

PURPOSE:To reduce noise, by controlling the driving pulse width of a switching element with the first control means and by changing the low frequency components in following up the full-wave rectification voltage waveform. CONSTITUTION:A power unit rectifies the AC input in full-wave with a rectification circuit 10 and applies it to a series circuit of a switching element Q1 and the primary winding L1 of a transformer 20. This element Q1 is turned ON and OFF for drive with a PWM circuit 31. As a result, the DC output is taken out of the secondary winding L2 of the transformer 20 through a wave filter circuit of a diode D1 and a capacitor C1. The wave signal of rectification output voltage V1 is inputted into a voltage control type variable gain amplifier 32, while the DC output voltage V2 is inputted into an error amplifier 35 respectively. The primary current I 1 is then detected by a current transformer 34 and the low frequency components are extracted with a filter 37 to input them into a differential amplifier 33. The PWM circuit 31 changes the driving pulse of the switching element Q1 so that the differential output may be minimum.

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 It is 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.

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 voltage to the DC-DC converter 3 will exceed the permissible range if it continues as it is, and the DC-DC converter 3 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.

(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, and a rectifier circuit that is driven on/off at a sufficiently higher frequency than the AC power source. a switching element, a transformer whose primary winding is connected in series with the switching element and between the outputs of the rectifier circuit, a filtering circuit that obtains a smoothed DC output from a secondary winding side of the transformer, 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 switching element, 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 that detects an error in the output voltage of the filter circuit with respect to a reference voltage and controls the driving pulse width of the switching element so as to reduce the error.

(Function) In the above configuration, the driving pulse width of the switching element is controlled by the first control means, and the low frequency component of the current flowing through the switching element and the primary winding of the transformer is converted into a full-wave rectified voltage waveform. It changes almost accordingly. Further, the driving pulse width of the switching element is controlled by the second control means, and the output voltage of the filtering circuit is kept 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.

A sine wave AC input is full-wave rectified by a rectifier circuit 10 made up of a diode bridge, and this rectified output is applied to a series circuit of switching element Q1 and primary winding L1 of transformer 20. This switching element Q1 is turned on/off by a PWM (pulse width control) circuit 31 at a frequency sufficiently higher than that of the AC power supply. As a result, energy is induced in the secondary winding L2 of the transformer 2o, the output on the secondary side is smoothed by a filter circuit consisting of a diode D1 and a capacitor C1, and a smoothed DC output is taken out from 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 waveform signal of the output voltage v1 of the full-wave rectification of the rectifier circuit 10 is V
The signal is input to a differential amplifier 33 via a CA (voltage controlled variable gain amplifier) 32. The primary current 11 flowing through the series circuit of the transformer primary winding L1 and the switching element Q1 is detected by the current transformer 34, and its low frequency component signal is extracted by the filter 37 and input to the differential amplifier 33. P.W.
The M 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.

Furthermore, the base of the output ground voltage V2 across the capacitor C1 is $
An error with respect to the voltage Vs 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 rectifier circuit 1
The waveform of the output voltage V1 of 0 and the waveform of the low frequency component of the current 11 on the primary side of the transformer 20 are compared, and the PW
The M 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 transformer primary winding L1 through the switching element Q1, and energy is stored therein. The amount of increase in current during this on-period is proportional to the input voltage (1) and proportional to the on-time.

When the switching element Q1 is turned off, a current due to the release of the energy stored in it flows to the secondary winding L2 side,
DC power is supplied to a load (not shown) through a filter circuit including a diode D1 and a capacitor C1.

As a result, the pulse width control based on the comparison between the input voltage waveform and the primary side current waveform (low frequency component) acts 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 v2 is than the reference voltage Vs, the more the VCA32
The smaller the gain of , and the smaller 2 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. That is, when the output voltage v2 is too high, the on time of the switching element Q1 is shortened, and on the other hand, when the output voltage v2 is too low, the on time is extended, which acts to bring the output voltage v2 closer to the reference voltage Vs.

In the above embodiment, the input and output are completely insulated by the transformer 20 and the photo-isolator 36, but the photo-isolator 36 is not required if there is no need for insulation.

(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.

Moreover, the feedback control action of the output voltage by the second control means described above allows the output voltage to be kept constant even when the AC input voltage fluctuates or the voltage rank is changed.

As a result, a power supply device that does not require any switching and is compatible with, for example, a 100 V AC power source to a 400 V AC power source 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... Transformer 31... Pulse width control circuit Patent applicant Fuji Electrochemical Co., Ltd. Agent
Person Patent Attorney - Ken Iro Jikan
Patent Attorney Masatoshi Matsumoto Figure 2'H3 Figure 1 and 4

Claims (1)

[Claims] (1) A rectifier circuit that full-wave rectifies an 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 primary winding connected in series with the switching element. A transformer connected in series between the outputs of the rectifier circuit, a filter circuit that obtains a smoothed DC output from the secondary winding side of this transformer, and a filter circuit that obtains a smoothed DC output from the secondary winding side of the transformer, and a filter circuit that controls the output voltage waveform of the rectifier circuit and the current flowing through the switching element. first control means for detecting the waveforms of the frequency components and controlling the drive pulse width of the switching element so that the current waveform follows the voltage waveform; A power supply device comprising: second control means for detecting an error and controlling the driving pulse width of the switching element so as to reduce the error.