Mains Powered Timer

056 MAINS POWERED TIMER This timer may be inserted in a power line to provide a controllable delay before a load is energized. It was developed to work in conjunction with a passive infra- red movement detector as part of an intruder alarm. The mains voltage is reduced by C3 and rectified to give about 30 V across Cl. This potential charges C2 slowly via R4-P1. When Ut2 reaches about 14 V, electronic switch T1-T2 actuates a solid- state relay (a Type S202DS from Sharp). When the mains voltage is removed,C2 discharges rapidly via D6 and R10. The delay extends from 15 s (P1 set to mini- mum resistance) to 5 min (P1 set to maxi- mum resistance). The solid-state relay needs cooling in accordance with the current drawn by the load: at up to 1 A no heat sink is re- L S a Fl N 0 Sib 894049.11 IA T RI C3 NNE 470n 400V R2 1W H „wol 1N4 C1 1N4 148 R3 1WH D3 8L 006 =1 mim An, D2 R10 BC547B S202D5 - 1000 1N40 T.000 W 405 006 1N4006 408 C4 GENERAL INTEREST D4 BC557B 05 ELEKTOR ELECTRONICS ...