DIAC
Diode for alternating current
Bidirectional
When avalanche breakdown voltage is achieved
◦DIAC goes from ON to OFF if operating in forward direction
◦DIAC goes from OFF to ON if operating in reverse direction
Structure
Four layer
Two terminals- MT1 and MT2
◦Both can be interchangeable as anode and cathode
No controlling element(like Gate)
Similar to pair of diodes facing towards each other.
Working
Depends on breakdown voltage of device
Conduction of current takes place immediately after exceeding breakdown.
At breakdown the resistance suddenly decreases creating a sharp voltage drop.
This drop increases the current conduction.
The diode will conduct up to holding current
Further increase in voltage drop brings the device to high resistance state
Characteristics
Dual characteristics- symmetrical forward and reverse characteristics
Conducts after breakdown voltage below which acts as an open switch.
Conducts until the current falls beneath holding current.
DIAC has negative resistance characteristics when conducting
◦Voltage decreases with increase in current
Applications
Light circuits to dim the light intensity
Trigger for TRIAC
Temperature control unit
Motor speed control.
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