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Publication numberUSH1319 H
Publication typeGrant
Application numberUS 07/671,594
Publication dateJun 7, 1994
Filing dateMar 19, 1991
Priority dateMar 19, 1991
Publication number07671594, 671594, US H1319 H, US H1319H, US-H-H1319, USH1319 H, USH1319H
InventorsThomas C. Stroup
Original AssigneeStroup Thomas C
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Current limit circuit for power supply regulators
US H1319 H
Abstract
Most power supply regulators either cause the output voltage to drop-off gradually, or caused output oscillation upon reaching or exceeding the limit current. Current limit feedback to an error amplifier within a switching regulator is used to control the output voltage, prevent oscillation, insure that current limiting does not occur until a well-defined threshold is achieved and then steeply limit the current. The circuit uses feedback to the switching regulator to maintain the output voltage within desired limits. The output current flows through the current limit resistor Rc thus providing a voltage proportional to the current at the base-emitter junction of Q1 via CR1 and R2. During normal operation, the forward biased CR1 voltage maintains a reverse bias on the B-E junction of Q1. When the voltage across Rc exceeds the forward bias on CR1, Q1 turns on, hence turning on Q2, thus providing its contribution to the current limit feedback circuitry for use by the switching regulator.
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Claims(1)
What is claimed is:
1. A circuit for regulating voltage in a power supply, comprising:
a power control circuit means for controlling a voltage of a power source,
a current limiting means for generating a feedback signal to said power control circuit means while limiting current to an output, and
a feedback circuit means for scaling a signal from a signal generation means to be sent to said power control circuit means.
Description
FIELD OF THE INVENTION

This invention pertains to a method and apparatus for limiting current in a power supply.

BACKGROUND OF THE INVENTION

Most prior art circuits either caused the output voltage to drop-off gradually, or caused output oscillation upon reaching or exceeding the limit current.

OBJECTIVES OF THE INVENTION

It is therefore a primary objective of the present invention to provide a circuit for regulating voltage of a power supply to provide good regulation of voltage up to a desired current limit value.

It is another objective to drop the voltage sharply above the desired current limit.

Still another objective is to avoid oscillation of the output voltage.

A further objective is provide a highly reliable circuit.

SUMMARY OF THE INVENTION

Current limit feedback to an error amplifier within a switching regulator is used to control the output current, prevent oscillation, insure that current limiting does not occur until a well-defined threshold is achieved and then steeply limit the current.

These objects of the invention and other objects, features and advantages to become apparent as the specification progresses are accomplished by the invention according to which, briefly stated, current limit feedback to an error amplifier within a switching regulator is used to control the output voltage and prevent oscillation.

LIST OF ADVANTAGES OF THE INVENTION

An important advantage of the present invention is that the circuit uses provides a square voltage-current curve.

Another advantage is that the circuit uses few components.

A further advantage is that most components of the circuit are fairly insensitive to component tolerances or parameters.

Still another advantage is that oscillation is prevented.

These and further objectives, constructional and operational characteristics, and advantages of the invention will no double be more evident to those skilled in the art from the detailed description given hereinafter with reference to the figures of the accompanying drawings which illustrate a preferred embodiment by way of non-limiting example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the circuit according to the invention.

GLOSSARY

The following is a glossary of circuit elements as referenced and employed in the present invention.

Q1 --2N2222A transistor

Q2 --2N2907A transistor

Q3 --2N3584 transistor

Q4 --2N3584 transistor

CR1,CR2--1N414B diodes

Rc --0.249Ω resistor

R1 --1000Ω resistor

R2 --16.2Ω resistor

R3 --4.99Ω resistor

R4 --499Ω resistor

R5 --3.01kΩ resistor

R6 --499Ω resistor

R7 --90.9Ω resistor

R8 --10kΩ resistor

C1, C2 --0.01 mfd capacitors

SR--switching regulator IC, e.g. Harris FG1532

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings wherein like reference numerals are used to designate like or corresponding parts throughout the various figures thereof, there is shown in FIG. I the circuit according to the invention.

The invention uses feedback to the switching regulator to maintain the output voltage Vout within desired limits. The output current flows through the current limit resistor Rc thus providing a voltage proportional to the current at the base-emitter junction of Q1 via CR1 and R2. During normal operation, the forward biased CR1 voltage maintains a reverse bias on the B-E junction of Q1. When the voltage across Rc exceeds the forward bias on CR1, Q1 turns on, hence turning on Q2, thus providing its contribution to the current limit feedback circuitry for use by the switching regulator SR.

R1 is a resistor that maintains the continuous forward bias current through CR1. R2 provides some current limiting for the base-emitter junction of Q1 during hard current limiting conditions and output current spikes. R3 prevents Q2 from being driven too hard by Q1. R4 provides a path for leakage current from the base-collector junction of Q2 thus helping to hold it off during normal operation. Capacitor C1 is simply a filter capacitor for the regulator output.

Within the feedback circuit, R5 and R6 scale the feedback signal to the power control circuit. C2 and CR2 are filters to reduce the noise to the power control circuit.

This invention is not limited to the preferred embodiment and alternatives heretofore described, to which variations and improvements may be made, without departing from the scope of protection of the present patent and true spirit of the invention, the characteristics of which are summarized in the following claims.

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US7098635Dec 31, 2003Aug 29, 2006Intel CorporationRegulating voltage applied to an integrated circuit and proxy frequency
Classifications
U.S. Classification323/282, 361/79, 323/277
International ClassificationG05F1/573
Cooperative ClassificationG05F1/573
European ClassificationG05F1/573
Legal Events
DateCodeEventDescription
Apr 2, 1991ASAssignment
Owner name: NAVY, THE UNITED STATES OF AMERICA, AS REPRESENTED
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:LOCKHEED MISSILES & SPACE COMPANY, INC.;REEL/FRAME:005657/0108
Effective date: 19910327