Series pass voltage regulator with overcurrent protection

• US 4,254,372 A
• Filed: 02/21/1979
• Issued: 03/03/1981
• Est. Priority Date: 02/21/1979
• Status: Expired due to Term

• Current Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Original Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Inventors: Moore, Chester A. Jr.
• Primary Examiner(s): Shoop, William M.
• Assistant Examiner(s): Wong, Peter S.
• Application Number:
  US06/013,141
• Time in Patent Office: 741 Days
• Field of Search: 323/9, 323/22 T, 323/4, 323/17, 323/DIG. 1, 361/18
• US Class Current: 323/277
• CPC Class Codes: G05F 1/573 with overcurrent detector

Abstract

A series pass voltage regulator compares the output voltage with a reference voltage and adjusts the base bias of a PNP series pass transistor coupled between an unregulated voltage source and a load to maintain the output voltage at a predetermined constant value. A current sensing resistor senses the base current of the PNP series pass transistor and limits the base current to a predetermined value indicative of a maximum allowable load current.

Claims

1. A voltage regulator having overcurrent protection comprising, in combination:

an input terminal adapted for connection to an unregulated voltage source;

an output terminal adapted for connection to a load;

a series pass transistor having base, emitter and collector electrodes, the emitter and collector electrodes being coupled between the input and output terminals for regulating the voltage at the output terminal;

means effective to provide a fixed reference voltage related to a desired regulated voltage at the output terminal;

an amplifying circuit responsive to the reference voltage and the voltage at the output terminal effective to control the current through the base electrode to a value producing substantially the desired regulated voltage at the output terminal, the base electrode current having a value that is indicative of the current supplied to the load through the series pass transistor;

a current sensing resistor series coupled with the base electrode, the current sensing resistor having a voltage thereacross that is a measure of the base electrode current and being indicative of the current supplied to the load through the series pass transistor; and

means responsive to the magnitude of the voltage across the current sensing resistor effective to limit the current through the base electrode of the series pass transistor to a predetermined value indicative of a maximum allowable current through the series pass transistor to thereby provide overcurrent protection.

2. A voltage regulator having overcurrent protection comprising, in combination:

an input terminal adapted for connection to an unregulted voltage source;

an output terminal adapted for connection to a load;

a series pass transistor having base, emitter and collector electrodes, the emitter and collector electrodes being coupled between the input and output terminals for regulating the voltage at the output terminal, the series pass transistor having a current amplification factor beta;

means effective to provide a fixed reference voltage related to a desired regulated voltage at the output terminal;

an amplifying circuit responsive to the reference voltage and the voltage at the output terminal effective to control the current through the base electrode to a value producing substantially the desired regulated voltage at the output terminal, the base electrode current having a value that is equal to the collector electrode current divided by the current amplification factor beta;

a current sensing resistor series coupled with the base electrode, the current sensing resistor having a voltage thereacross that is a measure of the base electrode current; and

means effective to limit the current through the base electrode of the series pass transistor when the voltage across the current sensing resistor is substantially equal to the maximum allowable collector electrode current divided by the current amplification factor beta multiplied by the resistance of the current sensing resistor to thereby provide overcurrent protection.

3. A voltage regulator having overcurrent protection comprising, in combination:

an input terminal adapted for connection to an unregulated voltage source;

an output terminal adapted for connection to a load;

a series pass transistor having base, emitter and collector electrodes, the emitter and collector electrodes being coupled between the input and output terminals for regulating the voltage at the output terminal, the current to the load being directly related to the base electrode current;

a current responsive amplifier effective to adjust the base electrode current of the series pass transistor in direct relationship with drive current supplied thereto;

means effective to provide a fixed reference voltage related to a desired regulated voltage at the output terminal;

a sensing circuit effective to sense the voltage at the output terminal and provide a voltage having a value directly proportional to the sensed voltage and equal to the fixed reference voltage when the sensed voltage at the output terminal is equal to the desired regulated voltage;

circuit means effective to compare the fixed reference voltage and the voltage provided by the sensing circuit and provide drive current to the current responsive amplifier having a value that is inversely related to the voltage provided by the sensing circuit;

a current sensing resistor series coupled with the base electrode, the voltage across the current sensing resistor being a measure of the base electrode current and being indicative of the current supplied to the load through the series pass transistor; and

means responsive to the voltage across the current sensing resistor effective to limit the drive current to the current responsive amplifier when the magnitude of the voltage across the current sensing resistor represents a base electrode current indicative of a maximum allowable current through the series pass transistor to thereby provide overcurrent protection.