Switchover system for binary load control

摘要

A system for alternately activating and deactivating a load comprises a high-resistance d-c circuit branch connected across a power supply downstream of a load-operating impedance, this branch including a voltage limiter and a voltage multiplier in series with each other and with a switching stage responsive to commands from a timer and/or a parameter sensor such as a thermostat. The junction of the voltage limiter and the voltage multiplier is connected to one input of a differential amplifier whose other input is energized with either of two potentials, respectively higher and lower than that of the junction, by the switching stage. The amplifier output controls a variable-resistance element, such as a transistor of the bipolar or the MOSFET type, connected across the high-resistance branch to form a current path in series with the load-operating impedance, the resistance of this path being variable between a high value minimizing the flow of load current and a low value sufficient to maintain the switching stage operational. A standby source may be provided for keeping the switching stage or at least an electric timer thereof energized during interruptions of the main power supply.