JPH06343263A - Synchronously rectifying converter - Google Patents

Abstract

PURPOSE:To obtain a synchronously rectifying converter in which a synchronously rectifying FET is not operated by a reverse current from the other DC power source when used as a parallel connection with an other DC power source. CONSTITUTION:A synchronously rectifying converter comprises a semiconductor switch 2 for converting a DC input voltage to a square wave pulse voltage to be applied to a primary winding of a transformer 3, and a synchronously rectifying FET 4, a diode 5, a choke coil 6, a capacitor 7, etc., for rectifying.smoothing a desired voltage pulse output from a secondary winding of the transformer 3 to output a DC voltage. A source of the FET 4 is connected to an input side of the coil 6, and a gate of the FET 4 is connected to an output side of the coil 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a synchronous rectification converter, and more particularly to a synchronous rectification converter that can be used in parallel with another DC power supply.

[0002]

2. Description of the Related Art Conventionally, a D using a synchronous rectification circuit of this type is used.
As the C-DC converter, as shown in FIG. 3, the DC voltage of the DC input power supply 1 is converted into a rectangular wave pulse voltage by the switching operation of the semiconductor switch 2, and the rectangular wave pulse voltage is converted into a desired voltage by the transformer 3. After being converted into, the rectification circuit is rectified and smoothed by the rectification circuit of the synchronous rectification element (synchronous rectification FET) 4 and the diode 5 and the smoothing circuit by the choke coil 6 and the capacitor 7, and the average value voltage is taken out. The above-described control of the switching operation of the semiconductor switch 2 is controlled by the voltage detection control circuit 8 which detects the output voltage of the synchronous rectification converter, based on the detection state. In a normal converter, diodes are used for the rectifying elements 4 and 5, but the synchronous rectifying converter of the present invention is a one-side synchronous rectifying system in which only the rectifying side is replaced with a field effect semiconductor switch (FET) as a synchronous rectifying circuit. It is intended for. As such a synchronous rectification converter, a large number of models having a small capacity to a large capacity are provided so as to be able to respond to the load capacity, and a synchronous rectification converter corresponding to the load capacity is selected and used.

[0003]

However, preparing a synchronous rectification converter according to the load capacity means increasing the number of models, which requires inventory for each model. It is desired to reduce the number of models from the viewpoint of design, production and article management, and it is considered to cope with a large capacity load by connecting the same model in parallel. However, the conventional synchronous rectification converter shown in FIG. The following problems occur when they are used in parallel connection or when other DC power supplies (such as batteries) are used in parallel connection.

That is, when another synchronous rectification converter of the same kind or an external DC power supply 11 such as a battery is connected in parallel to the output terminals 9 and 10 as described above, this other power supply connected in parallel is used. However, when the voltage becomes relatively higher than the output voltage of the synchronous rectification converter and the voltage detection control circuit 8 detects this and stops the operation of the semiconductor switch 2, or when the synchronous rectification converter protects the voltage. When the power supply is stopped due to the operation of the
The voltage of the external DC power supply 11 is supplied from 0 and is applied to the gate of the synchronous rectification FET 4, and the synchronous rectification F
The ET4 continues to be in the conducting state. This is because when an FET is used as the synchronous rectification element, if the bias of the gate is normal to the source potential, a current can flow between the drain and the source of the synchronous rectification FET 4 in either direction. The current flows back from the output terminals 9 and 10 and may be destroyed in due course. According to the present invention, the voltage of the external DC power supply 11 connected in parallel to the output terminals 9 and 10 becomes higher than the output voltage of the synchronous rectification converter of the main body, so that the synchronous rectification converter becomes inoperative. Even in the case, the synchronous rectification FET 4 is provided so as not to be turned on by the external DC power supply 11.

[0005]

A synchronous rectification converter according to the present invention converts a DC input voltage into a rectangular wave pulse voltage by a switching element and applies the rectangular wave pulse voltage to a primary side of a transformer.
In a synchronous rectification converter that rectifies and smoothes a desired voltage pulse extracted on the secondary side of the transformer with a synchronous rectification FET, a diode, a choke coil, a capacitor, etc., and outputs a DC voltage, the source of the synchronous rectification FET is The synchronous rectification FET is connected to the input side of the choke coil and the gate of the synchronous rectification FET is connected to the output side of the choke coil, and the synchronous rectification FET operates depending on an external DC power source connected in parallel to the synchronous rectification converter. It is something that is not done.

Another synchronous rectification converter according to the present invention is
The DC input voltage is converted into a rectangular wave pulse voltage by the switching element and applied to the primary side of the transformer, and the desired voltage pulse extracted on the secondary side of the transformer is synchronized rectification FET, diode, choke coil, capacitor. In a synchronous rectification converter that rectifies and smoothes a direct current voltage by outputting the direct current voltage, the source of the synchronous rectification FET is connected to the input side of the choke coil, and the output side of the choke coil and the secondary side of the transformer are connected. A plurality of diodes are connected in series with the end, and an interconnection point of the plurality of diodes is connected to the gate of the synchronous rectification FET. Depending on an external DC power supply connected in parallel to the synchronous rectification converter, This is to prevent the synchronous rectification FET from operating.

[0007]

1 is a circuit diagram showing a first embodiment of the present invention, and the same parts as those in the conventional example shown in FIG. In this embodiment, the synchronous rectification FET 4 is
Since the gate is connected to the output side of the choke coil 6 connected to the negative polarity line, if a normal rectangular wave pulse is output to the secondary side of the synchronous rectification converter, the synchronous rectification FET 4 will operate normally. It is supposed to work. However, when the voltage of the external DC power supply 11 connected in parallel becomes relatively higher than the output voltage of the synchronous rectification converter, the external DC power supply 11 stops operating when the synchronous rectification converter stops operating. Output terminals 9 and 10
The synchronous rectification FET 4 is not operated by the external DC power supply 11 because the positive voltage is not applied to its gate even if it is connected to the. Therefore, unlike the conventional synchronous rectification converter, there is no possibility that the synchronous rectification FET 4 is destroyed by the external DC power supply 11.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention, and the same parts as those of the first embodiment shown in FIG. 1 are designated by the same reference numerals. In the embodiment of FIG. 2, the gate of the synchronous rectification FET 4 is connected to the output side of the choke coil 6 connected to the negative polarity line through the diode 12, and the cathode side of the diode 5 is opposite to the diode 12 described above. The diode 13 is connected in the direction. That is, the diodes 12 and 13 are connected in series between the output side of the choke coil 6 connected to the negative polarity line and the positive polarity line on the secondary side of the transformer 3, and the interconnection points of the diodes 12 and 13 are connected. It is connected to the gate of the synchronous rectification FET 4.

Therefore, in the first embodiment shown in FIG. 1, the voltage applied to the gate of the synchronous rectification FET 4 in the operation of the present synchronous rectification converter has the positive and negative polarities generated in the choke coil 6. Both voltages are applied, but in the second embodiment shown in FIG. 2, only the positive voltage is applied, the negative voltage is blocked by the diode 12, and the gate by the diode 13 is applied during this period. Since the gate voltage is maintained at 0 by the discharge of, the amount of charge that charges and discharges the gate is greatly reduced and the conversion efficiency is improved.
However, in this embodiment, when the voltage is not generated in the choke coil 6, the impedance of the gate circuit of the synchronous rectification FET 4 becomes high, so that the resistor 14 and the diode 1
Needs 5 In each of the embodiments shown in FIGS. 1 and 2, the choke coil 6 is connected to the negative polarity line. However, a p-channel FET is used as the synchronous rectification FET 4, and the choke coil 6 is connected to the positive polarity line side. It is also possible to implement the present invention by connecting to.

[0010]

As described above, according to the present invention, the synchronous rectification FET of the present synchronous rectification converter is the same as that of the transformer.
It operates only by the rectangular wave pulse voltage generated on the secondary side, and prevents the synchronous rectification FET from operating by the external DC power supply connected in parallel with the synchronous rectification converter, enabling the parallel connection operation of the external DC power supply. In particular, the same type of synchronous rectification converters can be connected in parallel according to the load capacity, and it is possible to achieve the effect of reducing the number of types of synchronous rectification converters as well as the safety of operation.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a first embodiment of a synchronous rectification converter according to the present invention.

FIG. 2 is a circuit diagram of a second embodiment of a synchronous rectification converter according to the present invention.

FIG. 3 is a circuit diagram of a conventional one-sided synchronous rectification type synchronous rectification converter.

[Explanation of symbols]

 1 DC input power supply 2 Semiconductor switch 3 Voltage conversion transformer 4 Synchronous rectification FET 5, 12, 13, 15 Diode 6 Choke coil 7 Capacitor 8 Voltage detection control circuit 9, 10 Output terminal 11 External DC power supply 14 Resistance

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Naoki Murakami 1-1-6 Uchisaiwai-cho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (2)

[Claims] 1. A direct current input voltage is converted into a rectangular wave pulse voltage by a switching element and applied to a primary side of a transformer, and a desired voltage pulse taken out on the secondary side of the transformer is converted into a synchronous rectification FET and a diode. In the synchronous rectification converter that rectifies and smoothes by a choke coil, a capacitor, etc. and outputs a DC voltage, the synchronous rectification FET
Is connected to the input side of the choke coil, and the gate of the synchronous rectification FET is connected to the output side of the choke coil. 2. A direct current input voltage is converted into a rectangular wave pulse voltage by a switching element and applied to a primary side of a transformer, and a desired voltage pulse taken out on the secondary side of the transformer is converted into a synchronous rectification FET and a diode. In the synchronous rectification converter for rectifying and smoothing with a choke coil, a capacitor and the like to output a DC voltage, the synchronous rectification FE
The source of T is connected to the input side of the choke coil, and a plurality of diodes are connected in series between the output side of the choke coil and the other end of the secondary side of the transformer, and the diodes are connected to each other in series. A synchronous rectification converter characterized in that a connection point is connected to the gate of the synchronous rectification FET.