GB1453996A - Power supply and battery charging circuit for mains or battery operated electronic equipment - Google Patents

Abstract

1453996 Mains/battery supply systems; battery charging circuits SABA SCHWARZWAELDER APPARATE-BAU - ANSTALT AUGUST SCHWER SOEHNE GmbH 18 April 1974 [22 May 1973] 16942/74 Heading H2H A circuit for supplying power to equipment such as a portable television set from a mains supply, an external battery 3 or a built-in battery 17, comprises two change over contact assemblies 14, 15 and a voltage stabilizing circuit so that when the equipment is switched on a stabilized output voltage is supplied to the equipment and when the equipment is switched off an increased stabilized output voltage is supplied to charge the battery 17. When the equipment is switched on contacts a, b of the assemblies 14, 15 are closed and, assuming that a mains plug has not been inserted in a socket 1, contacts 22a, b are closed. A transistor 8, connected to a voltage divider 9, 10 and a zener diode 12, controls a transistor 7 which provides the equipment with a stabilized voltage derived from the battery 3 or 17. Alternatively, when the mains plug is inserted, contacts 22 b, c are closed to disconnect the battery 17 and supply the equipment with the stabilized voltage derived from a transformer 2 and a rectifier 6. When the equipment is switched off, the contacts b, c of the assemblies 14, 15 are closed and the output voltage is stabilized at a higher level by a voltage divider 18, 19 and a zener diode 20. This voltage charges the battery 17 via the closed contacts 15b, c and 22b, c. To prevent the battery 17 discharging through the contacts 22b, c, 15b, c, 14b, c and the voltage divider 18, 19 when the equipment is switched off and the mains plug is inserted but disconnected from the supply, transistors 25, 30 are provided, the transistors being non-conductive in these conditions.