This is a simple Temperature Controller Circuit Diagram with U217B. A triac controller for switching resistive loads directly from the mains supply using the zero crossing technique. The device is powered directly from the mains via a diode and dropper resistor, and the IC has its own regulator to limit its supply to 9.25V.
To ensure that no switching occurs outside of the zero crossing point, full wave logic is employed to guarantee that complete mains cycles only are switched to the load. A ramp a freely selectable ramp duration (as determined by a timing capacitor),together with the full-wave logic block, synchronised to the AC supply at pin 8 via a dropper resistor (RSync). The ramp generator not only provides symmetrical trigger pulse c .