Method and apparatus optically coupling thermostat to control a fan

摘要

An electrical circuit for controlling the activation of a fan includes optically coupled isolators. The circuit is electrically connected in series to a thermostat including a bimetal actuated contact with an anticipator across the contact. Power to the circuit is provided by voltage developed across the system relay coil in series with the thermostat. A zener diode establishes a threshold voltage consistent with the operation of the system relay coil and the thermostat. The optically coupled isolators provide the required electrical isolation needed to protect the thermostat from a power control circuit of an electronically controlled fan.