Abstract: An optical position transducer circuit for an electrical machine, for example a switched reluctance machine, comprises an optical transmitter, an optical sensor and an encoder disc in the path between the transmitter and the sensor. The disc is formed with apertures and light-blocking areas in between in accordance with a digital position code. The optical position transducer is energized by an enabling circuit. When the machine is not in use but in a standby mode, the enabling circuit is responsive to a signal from a controller to disable the transducer and to enable the transducer when an input demand signal is received from the controller. Selective enablement of the transducer considerably extends its lifetime and reduces current consumption in the standby mode.

Abstract: A temperature monitoring circuit comprises a thermistor which is connected with a power supply rail by means of a transistor. The transistor is pulsed to connect the thermistor intermittently in circuit with the power supply. The mean power drawn by the thermistor from the power supply is reduced, causing less drain on the power supply.