Two transistors on a regenerative switch are used to trigger a triac. This circuit is from the RCA Power Circuits manual. Transistors admit equivalents.
This battery-powered micropower supply was shown in Radio Electronics magazine in 1991. The...
Found in a 1965 Electronic Design, this circuit can be made with modern equivalent transistors. The...
In this circuit, the current in solenoid X1 can be adjusted and its intensity measured to the...