DC actuator control circuit with voltage compensation, current control and fast dropout period

A DC actuator system for a high current contactor comprising:

• a spring-biased DC actuator including a coil circuit for opening and closing contacts, the coil circuit having a switch controllable by a switch control signal;
• a voltage source;
• and
• control circuit means for controlling current to the coil circuit for providing sufficient armature force for contact closure and rapid dropout of the contactor to break welded contacts and for allowing pickup.

A control circuit for coil current in a spring biased DC actuator having a coil circuit receiving power from a voltage source, the control circuit comprising:

• an oscillator chopper circuit for periodically interrupting power to the coil, said oscillator controlled by a feedback amplifier sampling coil current;
• a sustaining current return circuit providing a current return for the coil when power is interrupted by the chopper;
• and
• a dropout switch in series with the coil and ground for opening the current return circuit responsive to removing power to the coil circuit.

A control circuit for coil current in a spring biased DC actuator having a coil circuit receiving power from a voltage source, the control circuit comprising:

• a switch in the coil circuit and controllable by a switch control signal to close the coil circuit;
• a power switching circuit connected to the switch to provide the switch control signal, the power switching circuit having
• a threshold detector providing a triggering signal for initiating operation of the control circuit responsive to a predetermined source voltage,
• a gate signal generator responsive to the triggering signal and having a time constant sufficient to drive the coil through a pickup interval,
• means for generating the switch control signal responsive to the gate signal and having a duty cycle determined by an oscillator controlled by a feedback amplifier sampling coil current for a first inrush level limit current and a second holding current responsive to the voltage of the voltage source;
• a sustaining current return circuit providing a current return for the coil when power is interrupted by the chopper;
• and
• a dropout switch in series with the coil and ground for opening the current return circuit responsive to removing power to the coil circuit.