What is a DIAC and how does it trigger conduction in both directions?
1 Answer
A DIAC, which stands for "diode for alternating current," is a two-terminal semiconductor device that conducts electrical current when a certain voltage threshold is reached. It is a type of bidirectional trigger diode that can conduct current in both directions. The DIAC is often used in conjunction with other components, such as TRIACs or thyristors, to control the conduction of alternating current (AC) in various electronic and electrical applications.
The behavior of a DIAC is based on its unique construction and doping profile. It is essentially a two-terminal, four-layer semiconductor device with a symmetrical structure. The two layers in the middle are typically lightly doped and have a high resistance. When a voltage is applied across the DIAC, initially, no current flows because of this high resistance.
However, as the voltage across the DIAC increases, it eventually reaches a critical voltage known as the "avalanche" or "breakover" voltage. At this point, the high electric field across the lightly doped layers causes them to break down, resulting in a sudden decrease in resistance. This allows current to flow through the DIAC in both directions, triggering conduction.
The key feature of the DIAC is its bidirectional behavior. Once conduction is triggered in one direction (forward or reverse bias), the DIAC essentially latches into a low-resistance state until the current drops below a certain level. This behavior is ideal for applications that require triggering of AC conduction in both directions, such as in light dimmers, motor speed controllers, and other power control circuits.
To summarize, a DIAC is a bidirectional trigger diode that conducts electrical current in both directions once a certain voltage threshold (avalanche or breakover voltage) is reached. Its unique construction and doping profile enable it to trigger conduction in response to AC voltage changes, making it useful in various electronic applications involving AC power control.
The behavior of a DIAC is based on its unique construction and doping profile. It is essentially a two-terminal, four-layer semiconductor device with a symmetrical structure. The two layers in the middle are typically lightly doped and have a high resistance. When a voltage is applied across the DIAC, initially, no current flows because of this high resistance.
However, as the voltage across the DIAC increases, it eventually reaches a critical voltage known as the "avalanche" or "breakover" voltage. At this point, the high electric field across the lightly doped layers causes them to break down, resulting in a sudden decrease in resistance. This allows current to flow through the DIAC in both directions, triggering conduction.
The key feature of the DIAC is its bidirectional behavior. Once conduction is triggered in one direction (forward or reverse bias), the DIAC essentially latches into a low-resistance state until the current drops below a certain level. This behavior is ideal for applications that require triggering of AC conduction in both directions, such as in light dimmers, motor speed controllers, and other power control circuits.
To summarize, a DIAC is a bidirectional trigger diode that conducts electrical current in both directions once a certain voltage threshold (avalanche or breakover voltage) is reached. Its unique construction and doping profile enable it to trigger conduction in response to AC voltage changes, making it useful in various electronic applications involving AC power control.