Two transistors on a regenerative switch are used to trigger a triac. This circuit is from the RCA Power Circuits manual. Transistors admit equivalents.
The circuit shown is from the Texas Instruments optoelectronics manual, applying to low power...
This circuit was found in a 1968 General Electric documentation. It has an input impedance of 2 M ohms...
This filter that rejects a frequency range determined by the double-T was found in the August 1993...