Circuit arrangement for detecting cross-over by an alternating voltage of a fixed reference voltage level

摘要

A circuit for detecting the crossings by an applied alternating voltage of two separate voltage threshold levels above and below a fixed reference voltage level. The circuit includes the series combination of two resistances (1 and 2) in an electrical path between the applied alternating voltage and a dc reference voltage. Two voltage comparators each having two logic output states compare the voltage at the junction (P) of the two resistances with the reference voltage so that the logic output state of the comparators at any instant is determined by the voltage at the junction relative to the reference voltage. A logic gate combines the logic output states of the comparators to produce a pulse spanning each instant of cross-over by the alternating voltage of the reference voltage. The pulse has a leading edge and a trailing edge which respectively correspond with the instants of crossing by the alternating voltage of the two separate threshold levels. One threshold level is determined by the magnitude of the reference voltage and the other by the ratio of the resistance values of the two resistances and the dc supply voltage. A circuit adapted for use in an replaces one resistor by a non- linear network.