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ACTIVE CURRENT LIMITER

IP.com Disclosure Number: IPCOM000024196D
Original Publication Date: 1979-Dec-31
Included in the Prior Art Database: 2004-Apr-02
Document File: 2 page(s) / 96K

Publishing Venue

Xerox Disclosure Journal

Abstract

An improvement to a regulated power supply is disclosed, which allows active surge protection while reducing the amount of power wasted by the conventional feedback resistor. With reference to the prior art of Figure 1, the unregulated voltage source 10 typically comprises a transformer 11, a rectifier bridge 12 and a capacitor 13. Transistor 14 is a power transistor often designated as a pass transistor. Amplifier 15 is a high-gain amplifier. An accurate reference voltage -V is applied to terminal 16. Transistor 17 is a small-signal PNP transistor. R%ltage shifting circuitry 18 is connected between transistors 14 and 17. During normal operation, transistor 17 is off and does not have any effect. Resistor 19 is the voltage dropping resistor. The regulated output voltage is available across terminals 20 and

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CEROX DISCLOSURE JOURNAL

ACTIVE CURRENT LIMITER Proposed Carlo Infante Classification

U.S. C1. 330/127

Int. CI. H03g 3/00

PRIOR ART

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- -

FIG. I

Volume 4 Number 6 November/December 1979 763

[This page contains 1 picture or other non-text object]

Page 2 of 2

ACTIVE CURRENT LIMITER (Cont'd)

An improvement to a regulated power supply is disclosed, which allows active surge protection while reducing the amount of power wasted by the conventional feedback resistor.

With reference to the prior art of Figure 1, the unregulated voltage source 10 typically comprises a transformer 11, a rectifier bridge 12 and a capacitor 13. Transistor 14 is a power transistor often designated as a pass transistor. Amplifier 15 is a high-gain amplifier. An accurate reference voltage -V is applied to terminal 16. Transistor 17 is a small-signal PNP transistor. R%ltage shifting circuitry 18 is connected between transistors 14 and 17. During normal operation, transistor 17 is off and does not have any effect. Resistor 19 is the voltage dropping resistor. The regulated output voltage is available across terminals 20 and


21.

During normal operation, any deviation from the correct output voltage is sensed by amplifier 15 and fed to transistor 14 in order to correct the value of the output voltage. If excessive current is drawn, this will result in a voltage appearing across resistor 19, thereby turning on transistor 17, which will limit the output current by decreasing the output voltage across terminals 20 and 21. The use of this prior art, regulated power supply is often difficult when designing high...