Low current consumption voltage supply threshold monitor - has bistable relay reset by charging current surge supplied via RC element

A circuit producing an output signal when a voltage supply exceeds a threshold level has a relay connected in the emitter-collector of a transistor. It consumes considerably less current than conventional quiescent current circuits without reducing response rate. This makes it more suitable for battery operation. The supply voltage (11) is connected across a parallel capacitor (3) which it charges via a diode (1) and series resistor (2). The transistor (5) is biassed off by a potential divider (4,6) connected across the supply voltage. The bistable relay (7) has a reset coil connected to the supply voltage via a further diode (8) and RC element (9,10). The latter is selected so that the relay resetting is caused by the charging current surge. Its discharge time constant is larger than its charging constant.