Regulator to Control Current Sharing among Parallel-Connected Power Transistors

摘要

A current regulator is described that controls the peak current of a power transistor driving the inductive load, such as magnet coils. Presently, the current pulse has a 0.1 to 1-ms adjustable duration with duty cycle to 5%. Ultimately, the pulse length must be approx. 7 ms with 50% duty cycle. The peak current nominally is 200 A, as set by a reference pulse. Several transistors, each controlled by an individual regulator, are connected in parallel to provide the total peak load current. The regulators compensate for differences between the power transistors and assure equal current sharing among the collectors. The regulator comprises an 8-bit multiplying digital-to-analog (D/A) converter that drives the base of the power transistor, an 8-bit up-down counter, an analog differencing circuit, and a comparator. For control purposes, a current-sensing resistor in the transistor's collector produces the second input to the differencing circuit. Regulation is accomplished over a collector current range of 200 +- 50 A per stage. (ERA citation 08:030143)