PROTECTIVE CIRCUIT FOR INTRINSICALLY SAFE ELECTROMAGNETIC EXECUTIVE DEVICES AND PROTECTIVE CIRCUIT FOR INTRINSICALLY SAFE POWER SUPPLY SYSTEMS

摘要

A protective circuit (30) for intrinsically safe electromagnetic actuators operating at the voltage of a power supply approved for underground mining, for switching electrohydraulic valves in underground mining, comprising a coil (11) connected to a first potential (2) and a second potential (3) of the power supply and associated with at least two spaced apart short-circuit means (12) connected in parallel with the electromagnetic actuator coil (11) for short-circuiting ting the coil in the event of a reversal of the potential of the coil voltage. In accordance with the present invention the protective circuit comprises a semiconductor switch (T3) which is inserted between the coil (11) and the second potential (3) and, in the event of a voltage reduction or potential reversal, isolates the coil (11) from the second potential, so that the discharge from the coil (11) has no adverse effect on the energy supply system or the intrinsic safety.