Emerson Electric Co.
Control circuits for supplying current to actuate gas valves in HVAC systems

Abstract:

A control circuit for supplying current to actuate a gas valve in an HVAC system includes a solenoid coil adapted to selectively open and close the gas valve, input terminals coupled to receive an AC power input, and a rectifier bridge coupled between the input terminals and the solenoid coil. The rectifier bridge includes four nodes and at least four diodes. The control circuit also includes a capacitor, and a switch coupled in series with the capacitor between a ground potential and a node defined between the rectifier bridge and the solenoid coil. The switch is coupled to selectively electrically connect and disconnect the capacitor in parallel with the solenoid coil to allow the capacitor to smooth the voltage rectified by the rectifier bridge when the switch is on and to inhibit smoothing of the rectified voltage by the capacitor when the switch is off.