JP2836382B2 - DC power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC power supply for converting an input voltage into a voltage by a voltage converter, and more particularly to a DC power supply capable of ensuring load protection under no load and light load.

[0002]

2. Description of the Related Art A conventional DC power supply will be described with reference to a circuit diagram of FIG. 4 and a power supply characteristic diagram of FIG.

In this DC power supply, when an input voltage is applied to a power supply input terminal 7, a voltage converter 1 converts the input voltage to a first DC voltage and outputs a first DC voltage to a converter output terminal, that is, a power supply output terminal 8.
Produces the same output voltage as the first DC voltage. A voltage divider composed of a series circuit of resistors 4 and 5 provided between the output terminal 8 and the ground terminal divides and detects a voltage corresponding to the output voltage, and outputs the divided voltage to a voltage dividing point P. Output voltage detection circuit. The control unit 2 controls the voltage conversion unit 1 based on the divided voltage. As a result of this control, as shown in FIG. 5, the voltage converter 1 generates the first DC voltage whose output voltage is stabilized regardless of the output current.

[0004]

In this conventional DC power supply, the output voltage with respect to the first DC voltage cannot be changed because the voltage conversion ratio from the output voltage to the divided voltage is constant. For this reason, this DC power supply has a problem in that it is not possible to perform control to reduce the danger to the load in the DC power supply with a high voltage output, that is, to perform control to lower the output voltage under no load and light load.

[0005]

A DC power supply according to the present invention has a power supply input terminal to which an input voltage is applied, and a voltage converter for converting the input voltage to generate a first DC voltage at a converter output terminal. A power supply output terminal that generates an output voltage corresponding to the first DC voltage, an output voltage detection circuit that detects a voltage corresponding to the output voltage, and a power supply terminal configured to generate the stabilized first DC voltage. In a DC power supply including a control unit that controls the voltage conversion unit based on a detection voltage, the output voltage detection circuit includes a first resistor inserted between the conversion unit output terminal and a power supply output terminal; A voltage divider that is connected between the power output terminal and the ground terminal and that divides the output voltage to a voltage dividing terminal and outputs the divided voltage as the detection voltage;
A field effect transistor (hereinafter referred to as an FET) having a drain terminal connected to the voltage dividing terminal, a source terminal connected to the power output terminal, and a gate terminal connected to the converter output terminal.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of one embodiment of the present invention, FIG. 2 is a graph showing a gate voltage vs. source-drain resistance characteristic of the FET 6 used in this embodiment, and FIG. 3 is a graph showing an output current versus output voltage characteristic of this embodiment. is there.

Referring to FIG. 1, this DC power supply is shown in FIG.
The power supply input terminal 7, the voltage conversion unit 1, the power supply output terminal 8, the voltage dividing circuit composed of the resistors 4 and 5, and the control unit 2 are the same as the DC power supply according to the prior art. This DC power supply also
A resistor 3 for detecting a load current (output current) inserted between the output terminal of the converter 1 and the power output terminal 8, a drain terminal connected to the voltage dividing terminal P, and a source terminal connected to the power output terminal 8. And an FET 6 for connecting the gate terminal to the output terminal of the conversion unit 1.

The operation of this DC power supply will be described. When no load is connected to the power supply output terminal 8,
Since no load current flows, no voltage is generated in the output current detecting resistor 3, and the gate-source voltage (hereinafter, gate voltage) of the FET 6 becomes zero. When the gate voltage is zero, as shown in FIG. 2, the resistance between the source and the drain of the FET 6 is low (point a in FIG. 2), and the divided voltage generated at the point P is high. Here, the control unit 2 controls the voltage conversion unit 1 so that the input voltage, that is, the divided voltage at the point P becomes constant. Therefore, in the above state, the output voltage generated at the power supply output terminal 8 becomes low (point a in FIG. 3).

On the other hand, when a load is connected to the power supply output terminal 8, a voltage is generated in the resistor 3 by the load current,
The gate voltage of No. 6 becomes +. When the gate voltage is sufficiently large, the resistance between the source and the drain of the FET 6 is large (point b in FIG. 2), and the divided voltage generated at the point P of the voltage divider corresponds to the voltage corresponding to the division ratio determined by the resistors 4 and 5. The output voltage at the power supply output terminal 8 is the set voltage (point b in FIG. 3).
become.

[0010]

As described above, in the DC power supply of the present invention, the source terminal and the drain terminal of the FET are connected in parallel to the high-potential-side resistor of the voltage divider. -Since the drain-to-drain resistance is reduced to reduce the voltage division ratio of the voltage divider and the output voltage, the danger to the load is reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of one embodiment of the present invention.

FIG. 2 is a graph showing a gate voltage vs. source-drain resistance characteristic of an FET 6 used in this embodiment.

FIG. 3 is an output current-output voltage characteristic diagram of this embodiment.

FIG. 4 is a circuit diagram of a DC power supply according to the related art.

5 is an output current-output voltage characteristic diagram of the DC power supply of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Voltage conversion part 2 Control part 3-5 Resistor 6 Field effect transistor (FET) 7 Power supply input terminal 8 Power supply output terminal

Claims (1)

(57) [Claims] 1. A power supply input terminal to which an input voltage is applied, a voltage conversion unit for converting the input voltage to generate a first DC voltage at a conversion unit output terminal, and an output corresponding to the first DC voltage. A power supply output terminal for generating a voltage, an output voltage detection circuit for detecting a voltage corresponding to the output voltage, and controlling the voltage conversion unit based on the detected voltage so as to generate the stabilized first DC voltage A DC power supply comprising: a first resistor inserted between the converter output terminal and a power output terminal; and a first resistor inserted between the converter output terminal and a power output terminal. A voltage divider that outputs the divided output voltage to a voltage dividing terminal and uses the divided voltage as the detection voltage; a drain terminal connected to the voltage dividing terminal; a source terminal connected to the power output terminal; and a gate terminal. To the converter output terminal. DC power supply, characterized in that it comprises a effect transistor.