DIAC

The DIAC is a diode that conducts electrical current only after its breakover voltage, V_BO, has been reached momentarily. The term is an acronym of diode for alternating current.

When breakdown occurs, the diode enters a region of negative dynamic resistance, leading to a decrease in the voltage drop across the diode and, usually, a sharp increase in current through the diode. The diode remains in conduction until the current through it drops below a value characteristic for the device, called the holding current, I_H. Below this value, the diode switches back to its high-resistance, non-conducting state. This behavior is bidirectional, meaning typically the same for both directions of current.