Motor vehicle windscreen wiper circuit - uses Schmitt trigger output to control auxiliary switching transistor base with input set by dry-wiper key switch

摘要

The electrical switching circuit in direct current network for a motor-driven vehicle is used to operate the windscreen-wipers during a stalling interval and a dry screen delay. The wiper motor with a pre-selected holding position-switch is controlled by closing the 'interval' switch or operating the drying-action switch. The output of a Schmitt trigger controls the base of an auxiliary transistor - acting as a switch - which has an inductive load, ie. relay. The emitter path is set at a supply voltage via the relay and the collector at a reference voltage. The input is controlled via a dry wiping-key-switch, time-gating circuitry ie. a RC - stage and a diode. The Schmitt trigger, is set a zero potential at the output and the transistor conducts, when an upper threshold value of 2/3 UB is attained at the input. The transistor during discharge of the capacitor via a resistor - at the reference potential - between the RC - stage and diode is parallel switched via a series network of resistances and diodes when the lower threshold value of 1/3 UB of the Schmitt trigger is attained.