DIAC
What is Diac?
The Diac is a combination of two diodes. It is a two terminal,three layer,bidirectional semiconductor device which can be switched from its OFF state to ON state for either polarity of applied voltage.
The two terminals are MT1 and MT2.
Circuit diagram:
The diac can be constructed in either pnp or npn form. In pnp form two leads are connected to p regions of silicon seperated by an n region.The structure of diac is similiar to that of a transistor.Howeverthere are some several important differences .
There is no terminal attached to the base layer.
The three regions are nearly identical in size.
The doping level at the two end P-layers is the same so that the device gives symmetrical switching characteristics for either polarity of the applied voltage.
Operation:
Diac circuits use the fact that a diac only conducts current only after a certain breakdown voltage has been exceeded. The actual breakdown voltage will depend upon the specification for the particular component type.
When the diac breakdown voltage occurs, the resistance of the component decreases abruptly and this leads to a sharp decrease in the voltage drop across the diac, and a corresponding increase in current.
The diac will remain in its conducing state until the current flow through it drops below a particular value known as the holding current. When the current falls below the holding current, the diac switches back to its high resistance, or non-conducting state.
Most diacs have a breakdown voltage of around 30 volts, although the exact specifications will depend upon the particular type of device.
Characteristics of a Diac:
Applications of Diac:
Diacs are used primarily for triggering of triacs in adjustable phase contril of a.c mains power.some of the circuit applications of diac are
The two terminals are MT1 and MT2.
Circuit diagram:
The diac can be constructed in either pnp or npn form. In pnp form two leads are connected to p regions of silicon seperated by an n region.The structure of diac is similiar to that of a transistor.Howeverthere are some several important differences .
There is no terminal attached to the base layer.
The three regions are nearly identical in size.
The doping level at the two end P-layers is the same so that the device gives symmetrical switching characteristics for either polarity of the applied voltage.
Operation:
Diac circuits use the fact that a diac only conducts current only after a certain breakdown voltage has been exceeded. The actual breakdown voltage will depend upon the specification for the particular component type.
When the diac breakdown voltage occurs, the resistance of the component decreases abruptly and this leads to a sharp decrease in the voltage drop across the diac, and a corresponding increase in current.
The diac will remain in its conducing state until the current flow through it drops below a particular value known as the holding current. When the current falls below the holding current, the diac switches back to its high resistance, or non-conducting state.
Most diacs have a breakdown voltage of around 30 volts, although the exact specifications will depend upon the particular type of device.
Characteristics of a Diac:
Applications of Diac:
Diacs are used primarily for triggering of triacs in adjustable phase contril of a.c mains power.some of the circuit applications of diac are
- Light dimming
- Heat control
- Universal motor speed control.
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