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To obtain full wave
operation, so that the
lamp can be provided
with the full ac supply
voltage, two thyristors
are required as shown.
Th1 is triggered during
the positive half cycles
of the ac supply, and
Th2 during the negative
half cycles.
The waveforms show the
thyristors being
triggered halfway
through each half cycle
and the current through
the lamp would be the
sum of the two currents.
The lamp will be at
about half brightness
A pulse generator and a
phase shift circuit is
necessary to provide
gate pulses which can
adjust the power from
minimum to maximum.
Since the gate voltages
have to be positive with
respect to the cathodes,
attention must be paid
to the polarity of the
gating pulses with
respect each other.
The high power ac
circuit can be isolated
from the control
circuits by means of
transformers or opto
isolators.
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