JP3586667B2 - Active clamp type multiple output power supply circuit - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a multiple output power supply circuit using a DC power supply, and more particularly to an active clamp type multiple output power supply circuit using an active clamp circuit.
[0002]
[Prior art]
Conventionally, in a power supply circuit using an active clamp system, when a multi-output power supply is configured by dispersing transformers, a circuit configuration shown in FIG. 3 is generally used.
Since the potential of the drive circuit of the high-side transistor in the active clamp circuit is different in each converter, a PWM control circuit and a pulse transformer are required, and the number of components is increased. As a result, miniaturization is hindered.
[0003]
[Problems to be solved by the invention]
On the other hand, Japanese Patent Application Laid-Open No. 2000-014136 “DC-DC converter” similar to the present invention is disclosed. This DC-DC converter has been developed for the purpose of a high-precision DC-DC converter in which output voltage fluctuation is suppressed, and includes a switch circuit for periodically turning on / off a DC current supplied to a primary winding of a transformer. A clamp circuit for limiting the voltage applied to the primary winding of the transformer and supplying a demagnetizing current to the primary winding of the transformer when the switch circuit is off, and a plurality of cycles output from the secondary side of the transformer. A plurality of synchronous rectifier circuits that respectively rectify the current and supply a demagnetizing current to the secondary winding of the transformer when the switch circuit is off; a plurality of smoothing circuits that respectively smooth their output voltages; A control circuit that detects one output voltage and gives a command to a switch circuit so that the output voltage becomes a predetermined constant voltage to perform loop control. .
[0004]
However, this DC-DC converter uses a single transformer and attempts to obtain a multi-output power supply circuit with a plurality of secondary windings. This is disadvantageous for dispersing heat and miniaturizing a transformer.
[0005]
An object of the present invention is to provide a multi-output power supply circuit in which a circuit is simplified in a multi-output power supply circuit using transformer dispersion using an active clamp circuit.
[0006]
[Means for Solving the Problems]
An active clamp type multi-output power supply circuit according to the present invention includes a DC input power supply circuit, a PWM control circuit for controlling power supply output of the DC input power supply circuit by a specific frequency and a pulse width, and an output transformer connected to the DC input power supply circuit. And a switching circuit that supplies power to the primary side of the output transformer under the control of the PWM control circuit, an active clamp circuit that actively clamps the primary side to demagnetize the output transformer, and a rectifier circuit that is connected to the secondary side of the output transformer. And a plurality of converters for each of the PWM control circuits, including a converter and a smoothing circuit . The high-side transistor of the active clamp circuit is a P-channel transistor,
The source terminals of the respective P-channel transistors are connected so as to be at the same potential, whereby active clamping is performed in parallel on a converter provided with a plurality of PWM control circuits.
[0007]
Further, the rectifier circuit may be a synchronous rectifier circuit using FET transistors.
[0008]
The means for performing the active clamp operation in parallel is that the high side transistor of the active clamp circuit is driven by a pulse transformer, and the active clamp operation is performed based on a reference point which is a common potential of each converter by using a P-channel transistor. It is characterized by doing.
[0009]
Further, the synchronous rectifier circuit has a first MOSFET for rectifying a secondary current of the output transformer and a second MOSFET for flowing a demagnetizing current to a secondary winding of the output transformer.
[0010]
Further, the DC input power supply unit outputs a smoothed DC voltage by full-wave rectification or half-wave rectification of a commercial frequency AC power supply.
[0011]
The present invention is a circuit configuration in an active clamp type power supply, and is particularly a circuit configuration effective for increasing the number of outputs by dispersing a transformer. Conventionally, when a multi-output power supply is configured by dispersing transformers, it is necessary to provide a primary-side PWM control circuit for each converter. Had become. Therefore, the present invention is characterized in that there is one primary-side PWM control circuit, and a P-channel FET is used for the high-side switch of the active clamp circuit, and each converter is active-clamped by one pulse transformer. Therefore, the circuit configuration is greatly simplified, and it is easy to increase the number of outputs by dispersing the transformer. Further, it is possible to easily disperse heat and reduce the size of the transformer, thereby achieving the effect of reducing the size of the power supply and improving reliability due to heat.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of the present invention.
[0013]
In this embodiment, a DC input power supply unit 1, a PWM control circuit 2 connected to the DC input power supply unit 1 and controlling the output of the converter based on a unique frequency and a pulse width, and an output transformer 12 controlled by the PWM control circuit 2 A switching circuit 10 comprising a transistor 10 for supplying a power pulse to the primary side; an active clamp circuit comprising a transistor 9 and a capacitor 11 for clamping the primary side for demagnetizing the output transformer 12; and a secondary side of the output transformer And a plurality of converters 18, 29, and 30 including a rectifying circuit including diodes 14 and 15 and a smoothing circuit including an inductor 16 and a capacitor 17.
[0014]
In particular, the number of the PWM control circuit 5 of the present invention is one, and the transistor 9 which is a P-channel FET is used for the high side switch of the active clamp circuit. 29 and 30 are characterized by performing an active clamp operation. Since the PWM control circuit 2 and the pulse transformer 5 can be shared by configuring the drive circuit of the high-side transistor 9 of the active clamp circuit with the common potential of each converter, the number of parts can be greatly reduced. As a result, multiple outputs can be easily realized by transformer dispersion.
[0015]
Next, the operation of this embodiment will be described with reference to FIG.
Each converter system of the present embodiment is a general forward converter, in which an input voltage obtained from a DC input power supply unit 1 is applied to a transformer 12 of a first converter 18, and an output is obtained by performing on / off control by a transistor 10. The winding 13 has a switching circuit for generating a predetermined AC voltage. Further, it has an active clamp circuit for resetting the transformer 12 by turning on / off the transistor 9. The drives of the transistors 9 and 10 are turned on / off at the frequency and pulse width obtained from the PWM control circuit 2. Further, the high side transistor 9 of the active clamp circuit is driven by the pulse transformer 5 and is configured based on the point a which is a common potential of each converter by using a P channel. Therefore, the second and third converters can also configure a similar circuit using the common PWM control circuit 2 and the pulse transformer 5.
[0016]
The DC input power supply unit 1 can be similarly configured with a DC input voltage obtained by performing full-wave or half-wave rectification on a commercial frequency AC power supply and smoothing it.
[0017]
The active clamp circuit is well known to those skilled in the art, and the detailed configuration and operation are omitted.
[0018]
Next, another embodiment of the present invention is shown in FIG. Although the basic configuration is as described above, the efficiency can be dramatically improved by rectifying the AC voltage obtained from the output winding 13 by using a synchronous rectification method using transistors (FETs) 31 and 32. It became. The same configuration is possible for the second and third converters.
[0019]
As shown in FIG. 2, the synchronous rectifier circuit includes a first MOSFET for rectifying a secondary current of the output transformer and a second MOSFET for supplying a demagnetizing current to a secondary winding of the output transformer. I have. The operation of the FET synchronous rectifier circuit is well known to those skilled in the art, and the description of the operation will be omitted.
[0020]
【The invention's effect】
According to the present invention, an active clamp circuit configuration has an effect that multiple outputs can be easily realized with a simple circuit configuration. Further, the heat is dispersed by the dispersion of the transformer, and the size can be reduced, and there is an effect that the reliability can be improved by the heat dispersion.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an embodiment of the present invention.
FIG. 2 is a circuit diagram showing another embodiment of the present invention.
FIG. 3 is a circuit configuration diagram showing a conventional example.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 DC input power supply unit 2 PWM control circuit 3, 4 capacitor 5 pulse transformer 6 resistor 7 diode 8, 19 input capacitor 9, 20 high side transistor (P channel)
10, 21 Transistor 11, 22 Capacitor 12, 23 Transformer 13, 24 Output winding 14, 25 Rectifying diode 15, 26 Commutating diode 16, 27 Smoothing coil 17, 28 Output capacitor 18 First converter 29 Second converter 30 3 converters 31-34 Synchronous rectification transistor (FET)

Claims (5)

DC input power circuit,
A PWM control circuit for controlling a power output of the DC input power circuit by a unique frequency and a pulse width;
And connected to the output transformer to the DC input power supply circuit, a switching circuit for supplying power under the control of the PWM control circuit on the primary side of the output transformer, is active clamp the primary side for the output transformer demagnetized An active clamp circuit; a converter provided for each of the PWM control circuits, including a rectifier circuit and a smoothing circuit connected to the secondary side of the output transformer ;
A high-side transistor of the active clamp circuit is a P-channel transistor;
An active clamp type multi-output power supply circuit in which the source terminals of the respective P-channel transistors are connected so as to have the same potential, whereby the PWM control circuit performs active clamp in parallel on the plurality of converters. . 2. The active clamp type multi-output power supply circuit according to claim 1, wherein the rectifier circuit is a synchronous rectifier circuit using an FET transistor. 3. The active device according to claim 2, wherein the synchronous rectifier circuit includes a first MOSFET for rectifying a secondary current of the output transformer and a second MOSFET for supplying a demagnetizing current to a secondary winding of the output transformer. Clamp type multiple output power circuit. 2. The active-clamp multi-output power supply circuit according to claim 1, wherein the DC input power supply section performs full-wave rectification on a commercial frequency AC power supply and outputs a smoothed DC voltage. 2. The active clamp type multi-output power supply circuit according to claim 1, wherein the DC input power supply unit performs half-wave rectification on a commercial frequency AC power supply and outputs a smoothed DC voltage.

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