a control circuit for controlling the current through an inductive load powered by a unipolar power source . the current through the inductive load is controlled by three electronic switches and a subcircuit . the switches provide three different voltage levels across the inductive load . the closing of the first switch supplies positive voltage across the load , thereby increasing the load current . opening of the first switch and closing of the third switch disconnects the power source from the load and short circuits the inductive load resulting in zero voltage across the load . opening of the third and first switches directs the inductive current through the subcircuit , developing a negative voltage across the load and thereby rapidly decreasing the inductive current . by controlling the load voltage between a positive and zero voltage and between a negative and zero voltage , the load current is changed quickly and efficiently .