The DB3 diode is an electronic component known as a trigger coupler diode (also known as a DIAC diode). It is a type of diode used to trigger a triac or a thyristor in a power control circuit. DIAC diodes are commonly used in power control circuits to control the power that is supplied to a load, such as a motor or lamp, via a triac or thyristor.

DIAC diodes have two terminals and are used in pairs to trigger a triac or a thyristor. When a voltage is applied to one terminal of the diode DIAC, a current is produced through the diode which gradually increases until it reaches a critical level, at which time a rapid discharge of current occurs through the diode. This current discharge is used to fire the triac or thyristor, allowing current to flow through the load.

DIAC diodes are very useful components in power control circuits and are used in a wide variety of applications, such as fluorescent lamps, lighting equipment, heating and air conditioning systems, and many other electrical and electronic devices.