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Floating Programmable Current Supply

IP.com Disclosure Number: IPCOM000076398D
Original Publication Date: 1972-Feb-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Frushour, JE: AUTHOR

Abstract

This circuit combines a constant-current source with the further advantage of being able to ground either side of the load (or neither side) and simultaneously limit the output voltage. The current supply is programmable with a range of from 10ua to 10MA and a selection of the output current direction is by remote control. In addition, the output current is limited to the desired programmed value regardless of the output voltage polarity, and is normally shorted until a signal is applied removing the output short.

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Floating Programmable Current Supply

This circuit combines a constant-current source with the further advantage of being able to ground either side of the load (or neither side) and simultaneously limit the output voltage. The current supply is programmable with a range of from 10ua to 10MA and a selection of the output current direction is by remote control. In addition, the output current is limited to the desired programmed value regardless of the output voltage polarity, and is normally shorted until a signal is applied removing the output short.

In operation, the voltage V1 is established by virtue of operational amplifier performance. The output current is then programmed by providing an uplevel on the appropriate gate (or gates). The circuitry comprised of D1, D2, etc., clamp the -20 floating-voltage supply within limits to enable the gate voltages to control T1 and T2. If, for example, the uplevel is provided on the gate of T1, the output current will be equal to Io = -20 -V(ref) over R1 provided currents li and Ig are neglected. For the field-effect transistor (FET), the value for lg is less than 10 picoamps (typical for MOS FETS) and for the operational amplifier, the value for Ii is 25 PA (typical for FET op AMPS) so that the aforementioned assumptions are valid.

FET 4 serves both to protect the load by shorting the current supply until a control signal is applied and as a control to shunt out a portion of the output current, whenever the output voltag...