Actuating cct for coil of electromagnetic valve - holding current maintained by phase angle varying arrgt

摘要

An electromagnet to operate a magnetic valve, actuated by an a.c. or pulsed d.c. current, has a coil (11) at the output of a rectifier bridge (13) and in series with a triac (14), which when actuated by closing the supply switch (15), passes a higher value current during approximately a half period, then afterwards the holding current through the coil falls to a lower value with an increase in the phase lead angle. This is controlled by an arrangement of a pulse emitter (16) connected by two branches (17, 18) to a zero current counter (19) connected to a voltage divider formed by two resistors (22, 23) across the supply forming a changeover system giving the change in the phase angle.