Voltage regulator with current limiting circuitry

• US 4,218,647 A
• Filed: 10/27/1978
• Issued: 08/19/1980
• Est. Priority Date: 10/27/1978
• Status: Expired due to Term

• Current Assignee: Unisys Corporation
• Original Assignee: Burroughs Incorporated (Terreno Realty Corp.)
• Inventors: Haas, Frank J.
• Primary Examiner(s): Miller, J. D.
• Assistant Examiner(s): Wong, Peter S.
• Application Number:
  US05/955,241
• Time in Patent Office: 662 Days
• Field of Search: 323/9, 323/20, 323/17, 323/DIG. 1, 363/50, 363/56, 361/18
• US Class Current: 323/268
• CPC Class Codes: H02H 9/02 responsive to excess current current limitation for voltage regulators G05F1/573; disconnection after limiting H02H3/025
• CPC Class Codes: H02M 3/3376 with automatic control of output voltage or current

Abstract

Voltage regulator having current limiting circuitry. The voltage regulator includes an operational amplifier which has a substantially high output impedance and is disposed in a negative feedback configuration to provide an output signal which is the difference between a reference voltage input and the magnitude of the output voltage of the voltage regulator. Overcurrent detection circuitry is connected to the output of the operational amplifier and provides an on or off signal whenever the magnitude of the current drawn by a load exceeds a predetermined magnitude. When the magnitude of the load current exceeds a predetermined magnitude, the output of the overcurrent detection circuitry will be a low level signal which clamps or draws down the magnitude of the output voltage of the operational amplifier towards ground potential. A resistor-capacitor series circuit connected between ground and the output of the operational amplifier integrates the digital signal and provides an analog signal proportional to the average magnitude of the output voltage of the operational amplifier. A portion of the magnitude of the analog signal is fed back through a resistor to the gain of the operational amplifier and cause the output voltage of the operational amplifier to be linearly reduced which, in turn, through the power amplification controlling circuitry of the voltage regulator linearly reduces the output current of the voltage regulator until the overcurrent condition is eliminated.

Claims

1. A voltage regulator having current limiting circuitry and receiving an unregulated input voltage from an electrical energy source and supplying a regulated D.C. voltage at its output, said voltage regulator comprising:

an operational amplifier means having an inverting input terminal, a noninverting input terminal and an output terminal, said operational amplifier having a substantially high output impedance;

reference voltage circuit means, connected as an input signal to said noninverting input terminal of said operational amplifier, for providing a reference voltage thereto;

power amplifier controlling means, connected to said electrical energy source and said output terminal of said operational amplifier means, for providing a regulated DC output voltage at its output;

means for connecting said output of said power amplifier controlling means as an input signal to said inverting input terminal of said operational amplifier means, with said operational amplifier providing at its output terminal an output signal that is the difference between said two input signals connected thereto;

overcurrent detection means, having on and off states, for detecting when the current drawn by a load exceeds a predetermined magnitude, said output of said overcurrent detection means being connected to said output terminal of said operational amplifier, said overcurrent detection means being operative to lower the magnitude of the output voltage of said operational amplifier means when said current drawn by said load exceeds said predetermined magnitude;

integrating means, connected to said output terminal of said operational amplifier means, for providing an average value of said magnitude of said output voltage of said operational amplifier means; and

feedback means, connected between said output terminal and said inverting input terminal of said operational amplifier means, for feeding back a portion of the magnitude of said output voltage of said operational amplifier means so as to modify the gain of said operational amplifier and cause a linear reduction in said magnitude of said output voltage of said operational amplifier means which acts, through said power amplifier controlling means, to linearly reduce the magnitude of the output current of said voltage regulator to a level sufficient to remove said overcurrent condition.

2. The voltage regulator of claim 1 wherein the feedback means includes resistance means.

3. The voltage regulator of claim 1 wherein the integrating means is a resistor-capacitor series network connected between the output terminal of the operational amplifier means and ground.

4. The voltage regulator of claim 1 wherein the overcurrent detection means includes:

a comparator means having an inverting input terminal, a noninverting input terminal and an output terminal;

a reference voltage circuit means, connected to said inverting input terminal of said comparator means, for providing a reference voltage thereto;

the output of the power amplifier controlling means connected to said noninverting input terminal of said comparator means; and

said comparator having on and off states for, when in said on state, providing an output signal indicating when the current drawn by a load exceeds a predetermined magnitude.