Electronic changeover device for DC-excited AC solenoids (coils) with a pick-up winding and a holding winding

摘要

The invention relates to an electronic changeover device for DC-excited AC solenoids with a pick-up winding and a holding winding. According to the invention, when the solenoid control voltage is present, a sensor (V10) detects the marginal field of the solenoid and, when the marginal field strength falls below a predetermined threshold value, initiates the changeover from pick-up to holding magnetomotive force. The specified circuit manages without an auxiliary contact and is configured in a very simple manner due to the digital changeover from pick-up to holding operation. In addition, the functions of overvoltage limitation, time-dependent protective disconnection, undervoltage protection, polarity reversal protection and temperature protection can be implemented with little expenditure. By switching the changeover device into the standby mode, the interference immunity is increased and the current consumption after completion of the switch-on operation is reduced. The entire control circuit including the sensor can be accommodated in a plastic cup, which is fixed on the outside of the apparatus, the sensor coming into the region of the solenoid marginal field which forms (Fig. 1). <IMAGE>