The Boeing Company

Tim R Majoch

Jeffrey A Krinsky

Disclosed is an electrical control circuit (10) for controlling current through a plurality of resistive loads (14(1), 14(2) . . . 14(N)). The control circuit includes a plurality of current control stages (12(1), 12(2), . . . 12(N)), a comparator circuit (18), and a plurality of diodes D.sub.1, D.sub.2. . . D.sub.N-1 in serial connection with the current control stages. The comparator circuit controls the current that is drawn collectively through the loads. The diodes ensure that all preceding current control stages in the series are conducting a predetermined level of current before the next current control stage begins to source current through its respective load. Each current control stage includes an operational amplifier (30), a pass transistor (34), a sense resistor (R.sub.s), and a feedback resistor (R.sub.f). The operational amplifiers are a pre-drive to the pass transistors to allow smaller sense resistors to be used, thereby providing greater efficiency. The feedback resistors (R.sub.f) provide feedback to the operational amplifiers.

Apparatus for controlling current through a plurality of resistive loads

Disclosed is an electrical control circuit (10) for controlling current through a furnace coil or other resistive load (14). The control circuit includes a plurality of current control stages (12(1), 12(2), . . . 12(N)), a minimum circuit (16), and a control system (22) which provides feedback from the load. The control circuit utilizes a signal conditioner (20) and a sensor (18) to provide information regarding the load to the minimum circuit. The minimum circuit provides the minimum of inputs from the control system and a limit circuit (24) to the current control stages, thereby controlling the current that is drawn through the load. Each current control stage includes an operational amplifier (30), a pass transistor (34), a sense resistor (R.sub.s), and a feedback resistor (R.sub.f). The sense resistors ensure that there is current sharing through each of the current control stages. The operational amplifiers are a pre-drive to the pass transistors to allow smaller sense resistors to be used. The feedback resistors (R.sub.f) provide degenerative feedback to the operational amplifiers.

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Puyallup, WA, United States of America

Tim R Majoch