Programmable micro-calculator for controlling domestic equipment - contains switching circuit to connect micro-calculator back up power supply when mains supply trips out

摘要

A power supply, comprising a mains transformer supplying a bridge rectifier, provides a stabilised voltage via a series regulating transistor. A back up power supply comprises a transistor in series with a battery with the transistor collector connected to the power supply rail. A cut out circuit contains a voltage detector comprising a zener diode whose cathode is connected to the regulated power supply rail. This zener provides a voltage when the mains regulates circuit operates. This causes a transistor to conduct and route the power to the micro calculator with its non volatile memory. An initialisation circuit interrupts the base drive to the series transistor in the back up circuit to prevent the battery from discharging when the mains supply is present.