Protection of a semiconductor controller with a downstream-connected converter transformer against excess current resulting from the occurrence of single-sided magnetisation of the converter transformer

摘要

A semiconductor controller with a downstream-connected converter transformer is protected, without the fuse which is connected upstream of the semiconductor controller triggering, against the occurrence of an excess current in the event of interruptions in the input AC voltage (UN) in that two immediately successive half-cycles of the input AC voltage are detected via a measurement transformer (1) and their voltage/time integrals are compared with one another. This is done by means of two integrators (2, 3) which supply the measurement voltages which are proportional to the voltage/time integrals to an element (4) which forms the difference between the two measurement voltages. If the difference between the two measurement voltages exceeds a value which is predetermined by a window comparator (5) a locking device (9) for the control pulses of the semiconductor controller is activated. <IMAGE>