JPH03218260A - Dc power supply for parallel operation - Google Patents

Abstract

PURPOSE:To prevent current from flowing in from other power supply at the time of non-operation by inserting an output switch comprising a power MOSFET into an output line, and turning the output switch ON upon generation of output voltage. CONSTITUTION:When a converter 1 operates to produce an output voltage V1, a voltage higher than V1 is produced on the secondary of a transformer T1 and a power MOSFET 6 is turned ON. When the converter 1 is not operating, no voltage is produced on the secondary of the transformer T1 and the output switch, i.e., the power MOSFET 6, is turned OFF. Consequently, current does not flow in from other power supply connected in parallel with a feeder line 5, and power loss due to the output switch can be reduced.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a DC power supply device for parallel operation in which a plurality of DC power supply devices are connected in parallel to a common load power supply path. In particular, the present invention relates to an improvement in a circuit that prevents current from flowing backward into the interior of another power supply device when in a non-operating state.

<<Prior Art>> A schematic configuration of this type of DC power supply device is shown in FIG. The converter 1 is controlled by the control section 2 and produces a DC output with a stabilized voltage 1. The DC output of converter 1 is connected to load 4 via backflow prevention diode 3.
It is connected to a power supply path 5 that leads to. Other power supply devices having a similar configuration are also connected to the power supply path 5, so that a plurality of power supply devices are connected in parallel to the power supply path 5, and power is supplied to the common load 4 by these power supply devices. When this power supply is in a non-operating state (no output voltage V1 of converter 1), the output line A diode 3 is inserted between the two.

<<Problems to be Solved by the Invention>> As is well known, a forward voltage drop Vf occurs in the diode 3, and if other power supply devices connected in parallel are not taken into account, the diode forward voltage drop Vf will be reduced from the output voltage v1 of the converter 1. A voltage V2 lowered by Vf is applied to the load 4. A Schottky diode is generally used as the diode 3, and the forward voltage drop Vf is about 0.55 volts.

Here, if the specified output voltage V1 is relatively low, for example 5 volts, the ratio of Vf to V1 will be 10% or more, and the power loss due to the diode 3 will be so large that it cannot be ignored. In other words, power loss in the diode 3 significantly reduces the efficiency of the power supply.

This invention was made in view of the above-mentioned conventional problems, and its purpose is to have a switch function that prevents current from flowing from other power supplies when it is not in operation, and to minimize power loss in the switch element. The object of the present invention is to provide a DC power supply device for parallel operation that is highly efficient and minimizes the number of parallel operations.

<<Means for Solving the Problems>> Accordingly, in the present invention, an output switch using a power MOSFET is inserted in the output line, and this output switch is turned on when an output voltage is generated.

<<Function>> When the power supply device is in a non-operating state, the output voltage is not generated, so the output switch of the power MOSFET is turned off to prevent current from flowing into the power supply device from other power supply devices. do.

The voltage drop due to the on-resistance of the MOSFET is smaller than the forward voltage drop of the diode.

<<Embodiment>> FIG. 1 shows a schematic configuration of a DC power supply device for parallel operation according to an embodiment of the present invention. The converter 1 is controlled by the control section 2 and generates a DC output with a stabilized voltage 1. In the converter 1, Q1 is a chopper switching element, T1 is a transformer, D1 and D2 are rectifier diodes, and L1 and 01 are a smoothing choke coil and a capacitor.

The output of the converter 1 is connected to an output terminal 7 via a power MOSFET 6 as an output switch, which is the main point of the present invention, and this output terminal 7 is connected to a power supply path 5 connected to a load 4. Another DC power source (not shown) is connected to this power supply path 5 in parallel with the power supply device.

A voltage taken out from the secondary side of the transformer T1 of the converter 1 is applied to the gate 2 of the power MOSFET 6 after being smoothed by a bias circuit including a diode D3, a capacitor C2, and resistors R1 and R2. When converter 1 operates to generate output voltage v1, a voltage higher than output voltage V1 is output to the secondary side of transformer T1, thereby turning on power MOSFET 6. If the specified value of the output voltage v1 is, for example, 5 volts, the power MOSFE
The source-drain voltage of T6 is approximately 10 volts,
FET 6 is biased sufficiently deep in the forward direction. FET6
By selecting one with appropriate characteristics, the on-resistance (resistance between the source and drain) of the FET 6 can be made very small. For example, if the voltage between Sos and drain is set to about 0.4 volts, the forward drop voltage of the diode is 0.5 volts.
It's considerably smaller than 5 volts. Therefore, power loss due to FET 6 is reduced.

Also, when converter 1 is inactive, transformer T
No voltage is generated on the secondary side of MOSFET 1, and power MOSFET 6 as an output switch is turned off.

Therefore, no current flows into the power supply device from other power supply devices connected in parallel to the power supply path 5.

5 <<Effects of the Invention>> As explained in detail above, the parallel operation DC power supply device according to the present invention has an output switch using a power MOSFET inserted in the output line, and this output switch is turned on when an output voltage is generated. Therefore, in a non-operating state where no output voltage is generated, the output switch is turned off, and no current flows into the power supply device from another power supply device connected in parallel. In addition, the on-resistance of a power MOSFET is smaller than that of a diode used for conventional backflow prevention, so even in a power supply with a low output voltage setting, the power loss caused by the output switch is extremely small, resulting in a highly efficient power supply. can do.

[Brief explanation of drawings]

FIG. 1 is a block diagram of main parts of a power supply device according to an embodiment of the present invention, and FIG. 2 is a block diagram of main parts of a conventional device. 1...Converter 2...Control unit 3...Reverse flow prevention diode (conventional) 6 4...Load 5...Power supply path 6 ...Power MOSFET (output switch) 7.
...output terminal

Claims (1)

[Claims] A DC power supply device for parallel operation, characterized in that an output switch using a power MOSFET is inserted in an output line, and the output switch is turned on when an output voltage is generated.