Structure operation and Characteristics of DIAC

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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