2N3055 sun switch - a power-photo transistor

july/august 1984 a power-photo transistor The 2N3055, strange though it may seem, can operate very well as.a photo transistor, as the circuit here shows. The power transistor must be made light sensitive, of course, and this is done by cutting off the top of the case. The light-sensitive area revealed is quite large enabling the "new" photo transistor to operate very effectively. The sunswitch is based on two tran- sistors, the decapitated 2N3055 (T1) and a switching transistor, T2. As long as no light (or not enough) falls on T1 this transistor does not con- duct. Resistor R1 then provides a base current for T2, which conducts and lights the lamp at the output of the circuit. When enough light falls on T1 it conducts and earths the base of T2 so the lamp extinguishes. The two transistors are coupled via R2 and P1 to improve the switching behaviour. The light intensity at which the cir- cuit switches is set by means of preset P1. 14 from an idea by H.J. Hooft 12V