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# Precision Current Clamp for Force Voltage Measurement Current Test Function

IP.com Disclosure Number: IPCOM000081950D
Original Publication Date: 1974-Sep-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 34K

IBM

## Related People

Hutson, DJ: AUTHOR

## Abstract

This circuit will automatically limit the current to some safe value when forcing a voltage to an unknown value of resistance, in a conventional force-voltage-measure current test function. The circuit performs a precision bidirectional current-clamp function at the output.

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Precision Current Clamp for Force Voltage Measurement Current Test Function

This circuit will automatically limit the current to some safe value when forcing a voltage to an unknown value of resistance, in a conventional force- voltage-measure current test function. The circuit performs a precision bidirectional current-clamp function at the output.

A maximum differential voltage across R1 is established for normal operating conditions. This voltage is a function of the range of current to be measured. Any differential voltage above the maximum means excessive current is flowing. The circuit clamps the differential voltage across R1 to a value just greater than the maximum value established under normal operating conditions, thereby eliminating the possibility of damage to any component or test probe in the test configuration.

Under normal operating conditions, V1 V4 V5 and V0' V OUT. V1 increases or decreases in magnitude with respect to V OUT, depending on how much current is flowing in or out of the pin under test. E3 = (V1V OUT) + delta V. Operational amplifiers 2 and 3 compare voltage V4 to (V OUT +/- E3) max. If V4 is more positive than (V OUT E3), then operational amplifier 2 will operate open loop and will saturate at a large negative voltage. Diode D1 will be reversed biased and normal operation is maintained.

If V4 is more negative than (V OUT E3), then operational amplifier 2 will operate closed loop and will clamp V4 to the value (V OUT E3). Operation...