With a 120 ohms resistor this circuit can also be used as a shield for 3.3 V output voltages. The circuit uses an opto-diac enabling the control of triacs connected to the power grid with total isolation.
This circuit is from a 90's Radio Electronics. The circuit operates accurately up to about 15 kHz...
This circuit is from a 1980s Signetics documentation but is valid for modern operating. Next to...
This circuit from a 1979 publication uses FETs which can be BF245 and integrated circuits, unlike...