Automatic controller for kitchen ventilator fan - responds to room illumination by using relay to switch ventilator fan motor off between mains and triac controlled by photodetector circuit

摘要

The automatic controller for ventilator fans used in domestic installations senses the illumination level in the kitchen to provide a higher air flow rate to remove cooking odours when the kitchen is occupied. When the kitchen illumination falls the fan motor speed is reduced after a set delay period. The fan motor (2) is supplied from the AC mains both through a triac (6) and directly through a relay contact. The triac is controlled by a circuit (15) which responds to the level of current in a photodetector (12). A timer circuit (13) in series with the photodetector detects the light change and maintains the control voltage for a set time. A relay (7) is activated while the photodetector is active, and switches the motor back to mains supply when the triac is not operating.