JPH11285245A - Power source unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent damages and malfunctions to a main power source by obtaining a secondary side output voltage in proportion to a primary side input voltage with a simple circuit constitution, and detecting an overvoltage and a reduced voltage in the primary side input, in a power source unit equipped with a main power source part provided with switching transistors Q1, Q2, a drive transformer T1, and a converter transformer T2, and an auxiliary power source part provided with a switching transistor Q3, and a flyback transformer T3 through which a current is made to flow intermittently by the transistor Q3. SOLUTION: The cathode of a rectifier diode D8 is connected with the anode side of a rectifier diode D7 as one end side of a secondary winding N2 of a flyback transformer T3 of an auxiliary power source part. A smoothing capacitor C7 is connected between the anode of the diode D8 and the other end of the secondary winding N2. When a switching transistor Q3 is in an on-state, an output voltage as a negative voltage is extracted, smoothed, and peak- rectified.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device such as a switching regulator comprising a main power supply and an auxiliary power supply.

[0002]

2. Description of the Related Art Conventionally, a power supply device having a main power supply unit and an auxiliary power supply unit has been configured, for example, as shown in FIG. FIG. 2 shows a power supply device using a current resonance type switching regulator as a main power supply unit. E1 denotes a DC power supply obtained by rectifying a commercial power supply voltage by, for example, a diode bridge rectifier circuit.

[0003] NPN switching transistors Q1 and Q2 are connected in series between the positive and negative electrodes of the DC power supply E1. Reference numeral 10 denotes an undervoltage detection circuit for detecting overvoltage and undervoltage of the primary input voltage. The intermediate point between the switching transistors Q1 and Q2 is the winding Nb0 of the drive transformer T1, the resonance capacitor C1, and the converter transformer T2.
Is connected to the negative electrode of the DC power supply E1 through the primary winding P of
A half-bridge type current resonance type switching circuit is configured.

The switching cycle of the switching transistors Q1 and Q2 is determined by the windings Nb1 and Nb2, capacitors Cb1 and Cb2, and resistor Rb of the orthogonal drive transformer T1.
The switching frequency is determined by a series resonance circuit composed of Rb1 and Rb2. Ro1 and Ro2 are starting resistances,
Co indicates a protection capacitor, and D1 and D2 indicate damper diodes.

A secondary winding S2, S3 and a tertiary winding S4 are wound on the output side of the converter transformer T2. The voltage induced in the secondary windings S2, S3 is a rectifier diode D2.
3, D4, and the voltage VO is applied to a predetermined circuit.
And a control circuit block (consisting of a control circuit and a protection circuit) 11 that detects a current and a voltage on the output side by the voltage VO and protects the main power supply unit. .

The voltage induced in the tertiary winding S4 of the converter transformer T2 is rectified by the diode D5, and the primary-side input voltage detected by the undervoltage detection circuit 10 is sent to the control circuit block 11. It is used as a drive power source for the photocoupler 12 for transmission. Note C
2 and C3 are smoothing capacitors.

T3 is a PWM which constitutes an auxiliary power supply unit.
This is the transformer of the flyback converter. One end of the primary winding N1 of the flyback transformer T3 is connected to the positive electrode of the DC power supply E1, and the other end is connected to the negative electrode of the DC power supply E1 via the switching transistor Q3.

A resistor R5 and a diode D6 are connected in series between both ends of the primary winding N1, and a capacitor C4 is connected to the resistor R5 in parallel. C5 is a smoothing capacitor. The voltage induced in the secondary winding N2 of the transformer T3 is rectified by the rectifier diode D7 and smoothed by the smoothing capacitor C6.

In the device configured as described above, the switching transistors Q1 and Q2 are on / off controlled by a predetermined switching frequency, and the current intermittent by the transistors flows to the primary winding P of the converter transformer T2. An output voltage is obtained from the secondary windings S2 and S3.

At this time, a resonance circuit is formed by the resonance capacitor C1 connected in series with the primary winding P of the converter transformer T2, and a maximum output voltage is obtained when the resonance frequency of the resonance circuit matches the switching frequency. As a result, the inductance of the drive transformer T1 is controlled.

That is, a voltage corresponding to the output fluctuation of the converter transformer T2 is detected by the control circuit block 11, and the control winding Nc added to the drive transformer T1 is detected.
By controlling the current flowing through the converter transformer T, the switching period is changed, and the control is performed in a direction to eliminate the output fluctuation of the converter transformer T2.

[0012]

In the power supply device shown in FIG. 2, when the input voltage on the primary side decreases, the main power supply unit lowers the switching frequency (oscillation frequency) to reduce the output impedance of the system, thereby reducing the output. The voltage is stabilized. However, if the input voltage on the primary side drops extremely, the switching frequency becomes lower than the resonance frequency of the system, and the switching transistors Q1 and Q2 cannot perform a zero-cross operation. Occurs.

To cope with this problem, a drop in the primary-side input voltage is detected, and (1) the relay is turned off; (2) the switching frequency is increased (away from the system resonance frequency); , Etc.

However, in either case, it is necessary to transmit a detection signal of the primary-side input voltage drop to the secondary side. For this reason, conventionally, components for transmitting signals between the primary and secondary such as the photocoupler 12 and a power supply for driving the components are required on the primary side, increasing the number of components and supplying power to the primary side. In order to obtain it, it was necessary to take measures such as providing a new winding on the transformer.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has as its object to obtain a secondary output voltage proportional to a primary input voltage by a simple circuit configuration so that an overvoltage of a primary input can be obtained. Another object of the present invention is to provide a power supply device that detects a decrease in voltage and prevents destruction and malfunction of a main power supply.

[0016]

(1) The present invention provides a main power supply unit having a switching element and a transformer, and an auxiliary power supply unit having a switching element and a transformer through which a current intermittently flows by the switching element. In the power supply device, the secondary winding of the transformer of the auxiliary power supply unit is provided with voltage acquisition means for obtaining a voltage proportional to a primary-side input voltage at a timing when a switching element of the auxiliary power supply unit is turned on. Wherein the overvoltage or undervoltage of primary input is detected based on the voltage obtained by the voltage acquisition unit, and the undervoltage detection unit detects the overvoltage or undervoltage of the primary power supply. A protection means for performing protection is further provided.

(2) According to the means described above,
Components such as a photocoupler for detecting the primary side input voltage and transmitting it to the secondary side are not required, and are proportional to the primary side input voltage without providing a dedicated winding in the transformer of the main power supply unit. The voltage can be obtained with a simple circuit configuration. Therefore, a protection circuit against overvoltage and undervoltage of the primary side input can be configured with a small number of parts.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, the same parts as those in FIG. 2 are denoted by the same reference numerals. In the present invention, as a means for obtaining a voltage proportional to the primary-side input voltage, a rectifier diode D8 is connected to the anode side of the rectifier diode D7 which is one end of the secondary winding N2 of the flyback transformer T3 of the auxiliary power supply unit.
And a smoothing capacitor C7 is connected between the anode of the diode D8 and the other end of the secondary winding N2.

Here, the voltage between the primary windings of the flyback transformer T3 is V1, the number of turns of the primary and secondary windings is N, respectively.
If the switching transistor Q3 is on, a voltage of V2 = (N2 / N1) V1 is generated between the secondary windings.

In the flyback converter, the rectifier diode D7 and the smoothing capacitor C6 are connected so that the output on the secondary side is taken out when the switching transistor Q3 is turned off. By connecting D8 to the opposite polarity to D7, An output can be taken out when the switching transistor Q3 is on. This is smoothed and the voltage of V2 is subjected to peak rectification, so that 1
A negative voltage proportional to the input voltage on the secondary side can be extracted.

The negative voltage thus taken out is monitored by the under-voltage detecting circuit 10 to detect the under-voltage or over-voltage of the AC input.
It is possible to protect the device from destruction by the protection circuit of (1).

As described above, according to this embodiment, a voltage proportional to the primary input voltage can be obtained on the secondary side by an extremely simple circuit having only two components. Therefore, for example, the conventional photocoupler 12 for signal transmission described in FIG. 2 and the tertiary winding S4 of the converter transformer T2 as a power supply for driving the photocoupler 12 are unnecessary.

[0023]

As described above, according to the present invention, a voltage proportional to the primary-side input voltage can be obtained on the secondary side with a very simple circuit configuration. can get. (1) A component such as a photocoupler for detecting the primary-side input voltage and transmitting it to the secondary side is not required.

(2) A primary-side power supply for driving the photocoupler is not required, and the transformer can be simplified.

(3) It is possible to configure a protection circuit against an undervoltage of the primary-side input with a smaller number of parts as described above.

(4) According to the above (1) to (3), it is possible to reduce the size and cost of the device.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a power supply device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional power supply device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Under voltage detection circuit 11 ... Control circuit block 12 ... Photo coupler E1 ... DC power supply T1 ... Drive transformer T2 ... Converter transformer T3 ... Flyback transformer Q1-Q3 ... Switching transistor D7, D8 ... Rectifier diode C6, C7 ... Smoothing Capacitor

Claims (2)

[Claims] 1. A power supply device comprising: a main power supply section having a switching element and a transformer; and an auxiliary power supply section having a switching element and a transformer through which a current intermittently flows by the switching element. A power supply device, wherein a voltage acquisition means for obtaining a voltage proportional to a primary-side input voltage at a timing when a switching element of the auxiliary power supply unit is turned on is provided in a secondary winding of the transformer. 2. An under-voltage detecting means for detecting an over-voltage or under-voltage of a primary-side input based on a voltage obtained by said voltage obtaining means, and said main power supply when said over-voltage or under-voltage is detected. The power supply device according to claim 1, further comprising a protection unit that protects the unit.