Abstract: A drive circuit including a motor for positioning a damper from a rest position to a stalled position and protect the drive mechanism from damage due to increased current to the drive motor when the damper stalls by including a current limiter to prevent the current in the motor from exceeding a predetermined value.

Abstract: A drive circuit including a motor for positioning a damper from a rest position to a stalled position and protect the drive mechanism from damage due to increased current to the drive motor when the damper stalls by including a current limiter to prevent the current in the motor from exceeding a predetermined value.

Abstract: A linear voltage-to-duty cycle converter is disclosed in which an input voltage to be converted is transformed to a triangle wave signal which has up and down ramps whose slopes are variable with the input voltage. A hysteresis comparator receives the triangle wave signal and produces a resulting output signal that has either a high value or a low value depending on the triangle wave signal condition. The time the resultant output signal is high or low compared to the overall time constitutes a duty cycle that is linear with respect to changes in the input voltage.

Abstract: A circuit to bypass the Zener diodes in the flyback circuit of a DC brush motor actuator which uses a voltage sensitive device to detect when the power to the motor is de-activated to control a switch that short circuits the Zener diodes.

Abstract: A spring return rotary actuator incorporating a DC brush commutated electric motor and a pulse width modulation drive circuit which reduces the voltage at which current is supplied to the motor once a rotation sensor senses that the actuator output shaft has stalled. The drive circuit also includes a temperature responsive feature which increases the voltage at which current is supplied to the motor in the event a sensed temperature exceeds a temperature limit.