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Constant Current Source for Energizing Active Inductive Loads

IP.com Disclosure Number: IPCOM000050858D
Original Publication Date: 1982-Dec-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 3 page(s) / 46K

Publishing Venue

IBM

Related People

Presley, DR: AUTHOR [+2]

Abstract

In certain circumstances a current source must exhibit stability while responding to signal voltage variations. Such instances occur when using inductive loads wherein it may be desirable to maintain a desired direct current magnitude in the load.

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Constant Current Source for Energizing Active Inductive Loads

In certain circumstances a current source must exhibit stability while responding to signal voltage variations. Such instances occur when using inductive loads wherein it may be desirable to maintain a desired direct current magnitude in the load.

Turning now to the drawing, a controlled or constant current source 40 is illustrated therein. An FET (field-effect transistor) amplifier 41 is controlled by an operational amplifier 42. The circuit illustrated uses the operational amplifier 42 and associated feedback as through resistor RS1 and associated capacitor C15 to maintain the desired current at DC and low frequencies. This circuit takes advantage of the high drain impedance of the FET 41 to maintain the desired current at high frequencies. A sample of the load variation across R48 (which is a sense resistor (RS)) allows the operational amplifier 42 to gate the FET and vary the circuit impedance to maintain a constant current in the load, in the present instance, series-connected phases of an inductive load, such as a step motor phase winding.

The controlling current magnitude may be established by a controllable reference. The controllable reference may be either operator controlled, as through a potentiometer R47 connected to a source of voltage +V, through resistor R46 or programmed with digital control through a digital to-analog (D/A) converter 47, as illustrated in the drawing. If a microprocessor is available, a controllable reference may be applied digitally by the microprocessor.

The overall control source stability is maintained by the operational amplifier 42 and the frequency compensation. The circuit ma...