This shield circuit is from a 1968s Motorola documentation. The relay is according to the supply voltage. R1 can be reduced to lower trigger voltages.
This circuit is suggested by a 1965 General Electric documentation. The triac must be in...
This circuit is from the 1990 Motorola Linear Databook. The integrated circuit used is the LF355,...
This circuit from an 80's publication also features low input capacitance. FET can be a modern...