High-efficiency programmable power supply

• US 4,893,228 A
• Filed: 11/02/1988
• Issued: 01/09/1990
• Est. Priority Date: 09/01/1987
• Status: Expired due to Fees

• Current Assignee: Hewlett Packard Company (HP Inc.)
• Original Assignee: Hewlett Packard Company (HP Inc.)
• Inventors: Wong, Siu B., Orrick, Herbert P.
• Primary Examiner(s): Salce, Patrick R.
• Assistant Examiner(s): Todd, Emanuel
• Application Number:
  US07/267,745
• Time in Patent Office: 433 Days
• Field of Search: 363/89, 323/265, 323/266, 323/268, 323/274, 323/275, 323/350, 323/351, 323/269, 323/270, 323/271, 323/272, 323/273, 323/279, 323/282, 323/283, 323/284
• US Class Current: 363/98
• CPC Class Codes: G05F 1/563 including two stages of regulation at least one of which is output level responsive, e.g. coarse and fine regulation
• CPC Class Codes: H02M 3/158 including plural semiconductor devices as final control devices for a single load

Abstract

A high-efficiency programmable power supply including a linear regulator and a switching pre-regulator. The switching pre-regulator monitors the voltage drop across the series pass regulator pass transistor and maintains a predetermined voltage drop thereacross. The programmable power supply output voltage is varied according to a digital signal applied to the linear regulator. The switching pre-regulator, in providing a generally constant voltage drop across the linear regulator pass transistor, increases efficiency of the power supply by reducing excess voltage which appears at the input of the linear series pass regulator to a minimum level below which the linear regulator can operate. Therefore, the power supply according to the present invention maintains high efficiency over a wide range of selectively programmed output voltages.

Claims

1. A power supply comprising:

a source of unregulated direct current;

an asynchronous switching pre-regulator receiving said unregulated direct current and providing a pre-regulated direct current output;

a linear regulator receiving said pre-regulated direct current and including a series pass element therein, and selectively providing a regulated output according to an externally applied control signal, wherein

said switching pre-regulator includes means for measuring the voltage drop across the series pass element, and is responsive to the measured voltage drop across said series pass element, providing a selectable pre-regulated direct current potential which maintains a selected voltage drop across said series pass element independent of external periodic signals.

2. The power supply of claim 1, wherein

said switching pre-regulator comprises a forward converter switching regulator.

3. The power supply of claim 1, wherein said linear regulator includes:

a series pass transistor; and

an amplifier connected to selectively activate said series pass transistor according to a signal representative of said regulated output and to said control signal.

4. The power supply of claim 3, wherein

said series pass transistor comprises a bipolar transistor, and the minimum voltage drop across the series pass transistor is 0.6 volts.

5. The power supply of claim 3 wherein

said linear regulator includes a digital-to-analog converter providing an analog signal to said amplifier, and receives a digital control signal as said control signal.

6. A power supply comprising:

a source of unregulated direct current;

an asynchronous switching pre-regulator receiving said unregulated direct current and providing a pre-regulated direct current output;

a linear regulator receiving said pre-regulated direct current and including a series pass element therein, and selectively providing a regulated output, wherein

said switching pre-regulator includes means for measuring the voltage drop across the series pass element, and is responsive to the measured voltage drop across said series pass element, providing a selectable pre-regulated direct current potential which maintains a selected voltage drop across said series pass element independent of external periodic signals.