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.
