Structure and principle of bidirectional trigger diode

Structure and principle of bidirectional trigger diode

Bidirectional trigger diodes are quite familiar to electronics enthusiasts. They can be seen in thyristor voltage regulation circuits and fluorescent lamp electronic rectifiers. This article compiles knowledge articles about bidirectional trigger diodes for everyone to learn and refer to.

Introduction to Bidirectional Trigger Diode

Bidirectional trigger diodes were developed simultaneously with bidirectional thyristors and are commonly used to trigger them.

In addition to triggering bidirectional thyristors, bidirectional trigger diodes are also commonly used in overvoltage protection, timing, phase shifting, and other circuits. Figure 2 shows an overvoltage protection circuit composed of bidirectional trigger diodes and bidirectional thyristors. The following diagram shows an overvoltage protection circuit:

When the transient voltage exceeds DIAC and Ubo, DIAC quickly conducts and triggers the bidirectional thyristor to also conduct, protecting the subsequent load from overvoltage damage. In addition to triggering bidirectional thyristors, bidirectional trigger diodes are also commonly used in overvoltage protection, timing, phase shifting, and other circuits. Figure 2 shows an overvoltage protection circuit composed of bidirectional trigger diodes and bidirectional thyristors. When the transient voltage exceeds DIAC and Ubo, DIAC quickly conducts and triggers the bidirectional thyristor to also conduct, protecting the subsequent load from overvoltage damage.

Introduction to Bidirectional Trigger Diode Part 2

The bidirectional trigger diode (diode AC switch), abbreviated as DIAC, has a characteristic curve as shown in the figure. From the structural diagram, it can be seen that DIAC is equivalent to a five layer diode composed of two parallel Schottky diodes connected in opposite directions. As the name suggests, it is a diode that can conduct in both directions, meaning that regardless of the polarity of the applied voltage, as long as the applied voltage is greater than the touch voltage VBO, it can conduct. Once it is turned on, to restore it to a disconnected state, the only way is to cut off the power supply or reduce its current and voltage to below the holding current and holding voltage.

Characteristic curve of bidirectional trigger diode

The electric shock voltage of DIAC is approximately between 20~40V, and it is commonly used as a trigger for bidirectional thyristor controlled rectifiers (TRIAC). Or as a relaxation oscillator.