The DB4 is a bilateral trigger diode (DIAC) from STMicroelectronics, designed to switch on when the voltage across it reaches the breakover threshold of 35 to 45 V. Once triggered, it conducts a peak output current of 2 A — enough to drive the gate of a medium-power TRIAC in phase-control circuits like dimmers, motor speed controllers, and heater regulators. The 50 µA breakover current is the minimum current needed to initiate conduction; below that level the DIAC remains in its high-impedance blocking state. This low trigger current means the RC timing network in a typical phase-control circuit can use smaller capacitors and higher-value resistors, reducing component size and cost.
Package and temperature — fitting the board and the environment
Housed in a DO-35 axial-lead glass package, the DB4 is a through-hole part that mounts directly into a PCB or can be soldered point-to-point. The glass body provides hermetic sealing, making it suitable for humid or condensing environments where plastic-packaged parts might absorb moisture.