Motor drive control circuit

A PWM motor drive control circuit for an electric power steering system, comprising:

• a bridge circuit having a pair of input terminals which are adapted to be connected to a DC electric power source, a pair of output terminals adapted to be connected to an electric motor, and four arms each defined by a transistor;
• a main control unit for producing a first continual direction control signal for activating a selected one of said transistors, and a torque control signal of a variable duty ratio for activating the transistor diametrically opposed to said selected transistor to activate said electric motor in a desired direction at a desired torque according to a steering command signal supplied thereto;
• a sub control unit for exclusively producing, as the only outputs thereof, at least one second direction control signal according to said steering command signal;
• and
• a gate drive control circuit for transmitting said first direction control signal and said torque control signal to said diametrically opposed transistors only when said first direction control signal produced by said primary control unit coincides with said second direction signal produced by said sub control unit.