Circuit for controlling application of electricity to a coil of an electric current switching apparatus

摘要

A control circuit (30) drives the coil (20) of a contactor (10) in response to a control voltage being applied. The control circui (30) t includes a power supply (31) that produces a regulated output voltage from the control voltage. The onset of the regulated output voltage starts a timer (34) which controls the width of pulses produced by a PWM controller (33). The pulses control a transistor (Q2) that applies the control voltage to the coil (20). Initially the pulses cause a high current to flow through the coil (20) to close the contactor (10) and after an interval of time the timer (34) signals the PWM controller (33) to shorten the pulses which applies lesser current to the coil to keep the contactor closed. A flyback circuit (36) provides a relatively low reverse voltage drop path in parallel with the coil (20) to maintain the electromagnetic field during the periods between the pulses. When the control voltage is removed to open the contactor (10), the flyback circuit (36) provides a high reverse voltage drop path to promptly dampen the coil current.