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Constant Current Circuit

IP.com Disclosure Number: IPCOM000073704D
Original Publication Date: 1971-Jan-01
Included in the Prior Art Database: 2005-Feb-22
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Hyland, RN: AUTHOR

Abstract

This circuit allows any power amplifier to be used as a controlled constant-current AC source. The provided source responds to changes in either a resistive or reactive load within a few microseconds.

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Constant Current Circuit

This circuit allows any power amplifier to be used as a controlled constant- current AC source. The provided source responds to changes in either a resistive or reactive load within a few microseconds.

A DC level controls amplifier 10 operation so that reactive phase changes in load 11 do not alter the supplied current amplitude.

For control of amplifier 10, current flow through inductive load 11 is sensed by current probe 12. Amplifier system 13 supplies a linearly amplified current-probe signal to peak detector 14. For providing additional load-impedance ranges, amplifier 13 may include selective frequency compensation and gain portions. Peak detector 14 includes high-speed matched diodes 15 and 16 respectively in its input and feedback portions. Variable-gain amplifier 17 receives the peak-detected signal in gain control portion 18. Voltage-responsive variable resistor 19 responds to the peak-detected signal for varying the gain of operational-amplifier stage 20. Diodes 21 limit the voltage across resistor 19. Oscillator 22 supplies a selected frequency sine wave to amplifier 17. Amplifier 17 supplies a variable-gain amplified sine wave to power amplifier 10 for regulating the load current amplitude at a predetermined magnitude.

The resistance of voltage-responsive variable resistor 19 decreases with the applied voltage. As the peak-detected voltage decreases, i.e., the current in load 11 decreases, resistor 19 increases its resistance...