Browse Prior Art Database

LOW CURRENT REGULATOR INPUT RANGE EXTENDER

IP.com Disclosure Number: IPCOM000005613D
Original Publication Date: 1986-Oct-01
Included in the Prior Art Database: 2001-Oct-19
Document File: 1 page(s) / 45K

Publishing Venue

Motorola

Related People

Dave Bush: AUTHOR

Abstract

Many electronic devices operating from a variety of power sources require regulators to supply fixed operating voltages. For low current applications, the ICL7663 programmable voltage regulator (by lntersil and others) is desirable in that it has a low input-output differential and low operating current. However, the input voltage of the ICL7663 regulator is limited to 16 volts. This limitation can present significant design constraints in low current systems.

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MO7VROLA Technical Developments Volume 6 October 1986

LOW CURRENT REGULATOR INPUT RANGE EXTENDER

by Dave Bush

   Many electronic devices operating from a variety of power sources require regulators to supply fixed operating voltages. For low current applications, the ICL7663 programmable voltage regulator (by lntersil and others) is desirable in that it has a low input-output differential and low operating current. However, the input voltage of the ICL7663 regulator is limited to 16 volts. This limitation can present significant design constraints in low current systems.

   The regulator input voltage operating range can be extended to the 40 to 50 volt range - without any cur- rent penalty - with the addition of a single JFET as a pre-regulator. As shown in the figure, the gate of the FET is connected to the regulator output, and the source of the FET is connected to the regulator input. The regulator then sees a voltage up to the FET pinchoff above the output. Furthermore, there is no source current flow through the pre-regulator to ground.

   The FET is selected to have a pinchoff smaller than the difference between the regulator maximum input voltage and the regulated output voltage, with an IDS greater than the maximum load current. For example, for a 5 vdcl20 mA load, a good choice would be the 2N4092 FET with a pinchoff of 3.5 volts and an IW of 55 mA. The breakdown of the FET would allow the circuit to be used with input voltages up to 30 volts.

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