GB1289753A - - Google Patents

Abstract

1289753 Switching systems for consumer devices S A O RYDBORN 17 Feb 1970 [18 Feb 1969] 7450/70 Heading H2H [Also in Division G1] A circuit for connecting and disconnecting a load such as an incandescent lamp L from a supply applied to terminals A, B, comprises a switch circuit including a unijunction transistor T3, a blocking circuit including a transistor T1 and adapted to prevent operation of the switching circuit at a predetermined ambient light intensity and a timing circuit adapted to disconnect the load from the supply after a predetermined time. On depression of push button switch S having an associated glow lamp G, a thyristor D5 becomes conductive and enables a capacitor C3 of the timing circuit to discharge through a resistance R7. The capacitor then begins to charge via a resistor R13 for the predetermined time but during the charging period the transistor T1 and a transistor T2 are non conductive so that the transistor T3 oscillates. A triac D1 therefore conducts so that the lamp is connected to the source. When the charge on the capacitor C3 reaches a certain level, the transistors T1, T2 become conductive so that the transistor T3 stops oscillating and therfore the triac D1 is switched off, thus disconnecting the lamp from the source. When the predetermined ambient light intensity exists, a light sensitive resistor R12 maintains the transistors T1, T2 conductive thereby preventing the lighting of the lamp. In a modification an increased number of transistors including a programmed unijunction transistor is used.