DIAC structure

When viewed the structure as shown below, not including DIAC thyristor family, but his principle of making it is classified as a thyristor. DIAC is made with structures similar to the PNP transistor. N layer on a transistor made so thin that electrons can easily penetrate across this layer. While at DIAC, N layer is made thick enough so that the electron is quite difficult to penetrate. DIAC structure which can thus also be viewed as two PN diode and the NP, resulting in some literature DIAC classified as a diode.

Difficult to be passed by two-way flow, DIAC was intended for this purpose. Only with a specific breakdown voltage before DIAC can conduct current. Current course can be delivered back and forth from the anode to the cathode and vice versa. DIAC same characteristic curve as TRIAC, but that just need to know is how its breakdown voltage.
Symbol of the DIAC is as shown in the image above. DIAC is generally used as a trigger ON the TRIAC to a specific input voltage is relatively high. An example is the following lamp dimmer applications in the figure below:


If it is known in the circuit TRIAC IGT of 10 mA and above the VGT = 0.7 volts. And note also that is used is a DIAC with VBO = 20 V, the TRIAC will be calculated on the ON voltage:
V = IGT (R) + VBO + VGT = 120.7 V

On a dimmer circuit, the resistor R is usually replaced with series resistors and potentiometers. Here with a series capacitor C R is used to shift the phase voltage VAC.