Control circuit for vapour extraction hood - by-passes speed control circuit when starting motor to ensure rapid start=up

摘要

The control circuit continuously controls the quantity of air conveyed by the extractor fan and exhibits short start-up times for the fan's ac motor whilst at the same time being cheap and simple. The motor (4) speed is controlled by a conventional speed control circuit (D). A start-up circuit (E) briefly bypasses the speed-setting component (16) of the speed control circuit when the motor is switched on. The speed control circuit resumes control of the speed after a given time has elapsed. This time is defined by the start-up circuit. The motor therefore starts more quickly than it would under the sole control of the speed control circuit.