GB1535321A - Washing machines - Google Patents

Abstract

1535321 Automatic electric control SERVIS DOMESTIC APPLIANCES Ltd 8 Jan 1976 [11 Jan 1975] 1245/75 Heading G3N A washing machine has a plurality of functional units e.g motors and valves, 12a, 12b &c., a logic circuit 10 which provides signals to energize them in accordance with instructions from a program selector and a gate controlled semi-conductor such as a triac Qlc controlling the application of an appropriate (mains) power supply to the functional units in response to signals from the logic circuit 10 via an output circuit, e.g. transistor TR1c. The logic circuit 10 is supplied with power at a suitable voltage e.g. from transformer Tl secondary L4, and stabilizing components ZD1, TR2 and C1. If any voltage spikes are generated by element 12c the logic circuit 10 is protected from them since they are attenuated in passing to the gate electrode of the triac Q1c and on arrival at the collector of TR1c are not communicated to its base. The breakdown voltage of the collector/base junction is arranged to be sufficient to prevent the passage of a damaging spike. Figure 4 (not shown) illustrates an alternative output circuit TRO1c employing an optical coupling which acts as a buffer between the input and output if a voltage spike occurs. In operation, transistor TR1c is normally held near cut-off by a biasing power supply L3, D1, D2 &c. on line 17. A pulse output from logic circuit 10 allows TR1c to conduct, gating Q1c on for a half cycle of the mains supply. The RMS power to the unit 12c depends on the proportion of each half cycle for which the triac is made to conduct.