JPH06327248A - One-transistor forward type multiple output converter - Google Patents

Abstract

PURPOSE:To PWM-control a second secondary output circuit synchronously with the PWM-control of a first secondary output circuit when the output voltage of the second secondary output circuit is deviated from a reference voltage, by feeding back the current corresponding to the difference between the output voltage and the reference voltage to the gate driving circuit of a FET. CONSTITUTION:A FET 23 is so connected respectively in series with the secondary winding of a transformer 4 of a secondary output circuit 2 and with a rectification diode 19 of the circuit 2 as to be interposed between them, and via a pulse transformer 10 of a control circuit 3, a semiconductor switching element 5 on the primary side of the transformer 4 and the FET 23 are controlled synchronously with each other. Also, the output voltage of the secondary output circuit 2 is sensed by voltage dividing resistors 20, 21, and the cathode current of a shunt regulator 15 is varied responding to the difference between the sensed output voltage and a reference voltage, and further, the cathode current is fed back to the gate driving circuit of the FET 23 through the amplification by a transistor 16. Subsequently, by the reset quantity of a saturable reactor 11 which is varied responding to the output voltage of the secondary output circuit 2, the FET 23 is controlled, and thereby, the output voltage of the secondary output circuit 2 is controlled independently of others.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-output converter which constitutes a DC power supply device necessary for communication devices, information processing devices and the like.

[0002]

2. Description of the Related Art A conventional multi-output converter uses a transformer provided with a plurality of secondary windings for a common primary winding, and as a method for stabilizing the output voltage of these secondary windings, A stabilizing circuit using a saturable reactor shown in 2 is used. There is an output circuit 1 and an output circuit 2 on the secondary side of the one-stone forward type transformer 4 shown in FIG.
The output circuit 1 feeds back the output circuit voltage, and the control circuit 3 causes the semiconductor switching element 5 on the primary side to PW.
M control is performed to stabilize the output voltage. In the output circuit 2, a saturable reactor 28 is inserted between the secondary winding and the rectifying diode 19, and the output voltage is detected via the voltage dividing resistors 20 and 21 provided in the output circuit, and the operational amplifier 24 Further, the difference voltage detected by comparing with the reference voltage 25 is fed back from the p-type transistor 26 via the diode 27 to the connection point between the saturable reactor 28 and the rectifying diode 19.

When the primary input voltage fluctuates, or when the output circuits 1 and 2 fluctuate in load, a cross regulation error occurs due to the resistance of the secondary winding and the voltage drop of the rectifying diode. To compensate for this, a voltage controlled magnetic amplifier including a saturable reactor 28 is used. That is, the saturable reactor 28 connected in series with the rectifying diode 19 in the output circuit 2
Is reset by a current applied through the p-type transistor 26 while the semiconductor switching element 5 provided on the primary side of the transformer 4 is off. The output voltage of the output circuit 2 is controlled and stabilized by adjusting the amount of reset magnetic flux of the saturable reactor 28.

[0004]

As described above, in the conventional multi-output converter, the saturable reactor is inserted in series with the output circuit. Therefore, in order to make a large current output circuit, it is necessary to increase the capacity of the saturable reactor, which increases the size of the saturable reactor, and if necessary, connect multiple saturable reactors in parallel. I had to do it. Also, in the case of a large output, it is necessary to configure each output circuit by a separate converter, so the number of circuit components increases, and considering adding a DC chopper to the Ichikoku forward converter,
An extra filter is needed. The present invention has been made to solve the above-mentioned drawbacks of the conventional multi-output converter, in which the saturable reactor may have a small capacity, and even if it is a single-stone converter, a plurality of secondary output circuits can be used. It is an object of the present invention to provide a forward type multi-output converter capable of configuring

[0005]

As described above, the one-stone forward type multi-output converter according to the present invention is a forward type in which the semiconductor switching element provided on the primary side of the transformer is shared by the secondary output circuits 1 and 2. The secondary output circuit 1 is a multi-output converter, and the secondary output circuit 1 is an ordinary forward converter that feeds back the output voltage and PWM-controls the semiconductor switching element on the primary side via the control circuit.
Further, the secondary output circuit 2 is one in which an FET is inserted in series with a rectifying diode in an ordinary forward converter, and the gate drive circuit of this FET is the secondary output circuit 1
The switching of the FET and the semiconductor switching element on the primary side is synchronized by connecting via the pulse transformer provided in the control circuit of the above, and the shunt regulator and the transistor provided in the output circuit of the secondary output circuit 1 are connected. The fluctuation of the secondary output voltage is fed back to the gate drive circuit of the FET via the reset circuit, and the saturable reactor connected in series with the gate drive circuit is reset.
The output voltage of the secondary output circuit 2 is controlled by controlling the ON width of ET.

[0006]

When the output voltage of the secondary output circuit 2 changes from the reference voltage, the current corresponding to the difference is fed back to the gate drive circuit of the FET through the shunt regulator and the p-type transistor. As a result, the reset amount of the saturable reactor also changes, so that the F
ET is PWM-controlled to adjust the output voltage of the secondary output circuit 2. Therefore, the secondary output circuit 2 is also PWM-controlled in synchronization with the PWM control of the secondary output circuit 1.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a single-stone forward type multi-output converter according to the present invention, in which the primary side circuit and the secondary output circuit 1 constitute a normal forward converter, which is the same as that in the prior art, and therefore its explanation is omitted. However, only different parts will be described.

The secondary output circuit 2 has a FET 23 connected in series between the secondary winding of a transformer 4 and a rectifying diode 19 in a normal forward converter. The gate drive circuit of the FET 23 is connected to the secondary circuit of the pulse transformer 10 provided in the control circuit 3 of the secondary output circuit 1 via the saturable reactor 11, the diode 14, and the p-type transistor 12. Further, the cathode terminal of the shunt regulator 15 in which the connection point of the voltage dividing resistors 20 and 21 connected in parallel between the smoothing reactor 18 and the smoothing capacitor 22 of the secondary output circuit 2 is connected to the REF terminal is p.
Connected to the base terminal of the p-type transistor 16, and the collector terminal of the p-type transistor 16 is the diode 1
4 is connected between the anode terminal and one terminal of the saturable reactor 11 to form a feedback circuit.

Since the secondary output circuit 1 is intended to stabilize the output voltage by the normal PWM control, the voltage control method of the secondary output circuit 2 will be described. Since the gate drive circuit of the FET 23 of the secondary output circuit 2 is connected to the secondary winding of the pulse transformer 10 provided in the control circuit 3 of the secondary output circuit 1, the semiconductor switching element 5 on the primary side The FET 23 is synchronously controlled by the control circuit 3. The output voltage of the secondary output circuit 2 is the voltage dividing resistor 20.
And 21 are input to the REF terminal of the shunt regulator 15, and the cathode current of the shunt regulator 15 changes corresponding to the difference with the reference voltage. This change in the cathode current is amplified by the p-type transistor 16 and fed back to the gate drive circuit of the FET 23.
The saturable reactor 11 and the diode 14 are connected in series, and since the feedback current flows into this connection point, the saturable reactor 11 is reset only in one direction,
The reset amount changes depending on the feedback current. Therefore, even if the semiconductor switching element 5 on the primary side is turned on, the saturable reactor 11 has a large inductance until the magnetic flux change corresponding to the reset magnetic flux amount by the saturable reactor 11 occurs,
No current flows through the gate drive circuit 23. That is, the ON / OFF of the FET 23 is controlled by the reset amount of the saturable reactor 11 fed back corresponding to the output voltage of the secondary output circuit 2, and the secondary output circuit 1 is synchronized with the secondary output circuit 1 and The output voltage of the output circuit 2 is independently PWM-controlled by the semiconductor switching element 5 on the primary side.

[0010]

As described above, the one-stone forward type multi-output converter according to the present invention performs the PWM control by synchronizing the secondary output circuits 1 and 2 with the semiconductor switching element provided on the primary side. The secondary output circuit 1 is a normal forward converter, but the secondary output circuit 2 is provided with an FET connected in series with a rectifying diode, and the gate drive circuit of this FET is used as the control circuit of the secondary output circuit 1. Synchronous control is performed via a pulse transformer provided, and on / off of the FET is controlled by a saturable reactor inserted in this gate drive circuit. Since this saturable reactor only controls the gate pulse of the FET of the secondary output circuit 2, even a large capacity secondary output circuit can be configured with a small saturable reactor. Therefore, one converter can be configured even with multiple outputs of several hundred W, and there is no need to use two converters according to the conventional method, and the circuit configuration can be simplified.

[Brief description of drawings]

FIG. 1 is a block diagram of a single-stone forward type multi-output converter according to the present invention.

FIG. 2 is a block diagram of a conventional one-stone forward type multi-output converter.

[Explanation of symbols]

 3 Control Circuit 4 Transformer 5 Semiconductor Switching Element 11 Saturable Reactor 12, 16 p-type Transistor 15 Shunt Regulator 23 FET

Claims (1)

[Claims] 1. A forward type multi-output converter in which a semiconductor switching element provided on the primary side of a transformer is shared by the secondary output circuits (1) and (2), wherein the secondary output circuit (1) is Two diodes that make up,
An output circuit voltage in a forward converter composed of a capacitor and a reactor is fed back, and the primary side semiconductor switching element is PWed through a control circuit.
The output voltage of the secondary output circuit (1) is controlled by M control, and a semiconductor switching element connected in series is provided on the anode side of the rectifying diode forming the forward converter in the secondary output circuit (2). The semiconductor switching element and the semiconductor switching element on the primary side are connected by connecting the gate drive circuit of the semiconductor switching element via a secondary circuit of a pulse transformer provided in the control circuit of the secondary output circuit (1). And the reset current of the saturable reactor connected in series between the secondary circuit of the pulse transformer and the gate drive circuit of the semiconductor switching element to the smoothing reactor in the secondary output circuit (2). Via a shunt regulator and a transistor between the smoothing capacitors Controls the on width of the FET by settling, Ichiseki forward type multiple-output converter that the output voltage, characterized in that the constant voltage control of the secondary output circuit (2).