Reference voltage generating circuit in a DC power supply

• US 4,321,525 A
• Filed: 01/02/1980
• Issued: 03/23/1982
• Est. Priority Date: 10/11/1978
• Status: Expired due to Term

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Hattori, Masayuki, Nakamura, Shigeo, Imazeki, Ryoji
• Primary Examiner(s): BEHA JR, WILLIAM
• Application Number:
  US06/109,118
• Time in Patent Office: 811 Days
• Field of Search: 307/356, 307/360, 307/361, 323/22 T, 323/8, 323/94 R, 323/22 Z, 323/273, 323/281, 323/349
• US Class Current: 323/281
• CPC Class Codes: G05F 1/468 characterised by reference voltage circuitry, e.g. soft start, remote shutdown

Abstract

A reference voltage generating circuit in a DC power supply includes a differential amplifier for detecting a difference voltage between a reference voltage and the output voltage, and a voltage control circuit which is responsive to an output signal from the differential amplifier so as to control the DC power supply output voltage to limit the difference between the output voltage and the reference voltage to zero. More specifically, the reference voltage generating circuit includes a reference voltage source, a first variable resistor connected in parallel with the reference voltage source, a second variable resistor connected to the negative side of the reference voltage source, a third variable resistor connected to the positive side of the reference voltage source, and a switching circuit for connecting a movable contact piece of the first variable resistor to either the second or third variable resistors, or to neither of them. A predetermined voltage of a magnitude greater than, equal to or less than a rated value can be delivered as a reference voltage at the movable contact piece of the first variable resistor by selecting from a plurality of preadjusted voltage divider circuits using a single selection operation.

Claims

1. A reference voltage generating circuit in a DC power supply which generates an output voltage, comprising:

a reference voltage source for generating a reference voltage;

a first variable resistor connected in parallel with said reference voltage source at first and second nodes and having a movable contact piece which acts as a tap to provide a tapped reference voltage;

a differential amplifier, operatively connected to said movable contact piece, for detecting a difference voltage between the tapped reference voltage and the output voltage and for generating a differential output signal;

a voltage control circuit, operatively connected to said differential amplifier and responsive to the differential output signal from said differential amplifier, for controlling the output voltage so as to limit the difference between the tapped reference voltage and the output voltage to zero;

a second variable resistor having a first terminal connected to the negative side of said reference voltage source at said second node and having a second terminal;

a third variable resistor having a first terminal connected to the positive side of said reference voltage source at said first node and having a second terminal; and

switching means for selectively connecting said movable contact piece of said first variable resistor to the second terminal of said second variable resistor, or to the second terminal of said third variable resistor, or to selectively disconnect said movable contact piece from said second variable resistor and said third variable resistor, so that the tapped reference voltage of said movable contact piece of said first variable resistor is a preset voltage having a magnitude greater than, equal to or less than a predetermined voltage.

2. A reference voltage generating circuit according to claim 1,

wherein said first variable resistor has a first leg connected between said first node and said movable contact piece and a second leg connected between said second node and said movable contact piece,

wherein said second variable resistor is independently adjustable so that when said switching means connects the second terminal of said second variable resistor to said movable contact piece, a first voltage divider circuit, including said second variable resistor and the first leg of said first variable resistor, is formed, wherein the preset voltage produced at said movable contact piece is a first predetermined and independently adjusted reference voltage,

wherein said third variable resistor is independently adjustable so that when said switching means connects the second terminal of said third variable resistor to said movable contact piece, a second voltage divider circuit, including said third variable resistor and the second leg of said first variable resistor, is formed, wherein the preset voltage produced at said movable contact piece is a second predetermined and independently adjusted reference voltage,

whereby said switching means provides one of said predetermined voltage, said first predetermined and independently adjusted reference voltage, and said second predetermined and independently adjusted reference voltage as said tapped reference voltage.

3. A reference voltage generating circuit according to claim 1 or 2, wherein said switching means comprises:

a movable switch contact having a first end connected to said movable contact piece of said first variable resistor and having a second end movable to one of first, second, and third positions, wherein in said first position the second end of said movable contact piece is connected to the second terminal of said second variable resistor, wherein in said second position the second end of said movable contact piece is connected to the second terminal of said second variable resistor and wherein in said third position the second end of said movable contact piece is connected to provide the predetermined voltage; and

a drive circuit, operatively connected to the second end of said movable switch contact, for moving the second end of said movable switch contact to one of said first, second, and third positions in dependence upon an externally applied drive signal.

4. A reference voltage generating circuit according to claim 1 or 2, wherein said second and third variable resistors comprise rheostats for finely adjusting the tapped reference voltage.

5. A reference voltage generating circuit according to claim 1 or 2, wherein said reference voltage source comprises first and second reference voltage sources, wherein the voltage difference between said first and second reference voltage sources is divided to produce the tapped reference voltage.

6. A reference voltage generating circuit according to claim 1 or 2, further comprising means for increasing the stability of the tapped reference voltage, including a resistor connected in series with said movable contact piece.

7. A reference voltage generating circuit according to claim 3, wherein said switching means includes means for operating said switching means in one of a manual and automatic mode.

8. A reference voltage generating circuit according to claim 5, further comprising means for increasing the stability of the tapped reference voltage, including a resistor connected in series to said movable contact piece.