Found in a Popular Electronics from the 90s, this circuit applies to flashes with xenon lamps. The transistor admits equivalent and the phototransistor is of the Darlington type.
Two operational amplifiers are used in this source obtained in an American documentation...
This circuit is suggested by the Linear Applications Handbook of National Semiconductor, being used...
This simple circuit for headphones or small speakers was found in documentation from the 90s. The...