Data Sheet

©2006 Fairchild Semiconductor Corporation www.fairchildsemi.com
FODM30XX Rev. 1.2 9
FODM30XX — 4-Pin Full Pitch Mini-Flat Package Zero-Cross Triac Driver Output Optocouplers
If sufficient holding current is still flowing through the
opto-TRIAC, the opto-TRIAC will turn-on and attempt
to carry the power TRIACs load. This situation typically
causes the opto-TRIAC to operate beyond its
maximum current rating, and product and resistor
failures typically result. For this reason, using an opto-
TRIAC to drive a three quadrant “snubberless” power
TRIAC is not recommended.
Power in the 360Ω resistor, when driving a sensitive
gate 4 quadrant power TRIAC:
I
GT
= 20mA
V
GT
= 1.5V
DF = 0.6%
P = (I
GT
+V
GT
/ 330Ω)
2
x 360Ω x DF
P = (20mA + 1.5
/ 330Ω)
2
*x 360Ω x 0.6% = 1.3mW
A 1/4 watt resistor is more than adequate for both the
360Ω and 330Ω resistors.
The real power in the snubber resistor is based upon
the integral of the power transient present when the
load commutes. A fast commuting transient may allow
a peak current of 4A to 8A in the snubbing filter.For
best results, the capacitor should be a non-polarized
AC unit with a low ESR. The 39Ω seriesresistor sets
a time constant and limits the peak current. For a
resistive load with a power factor near unity, the
commutating transients will be small. Thisresults in a
very small peak current given the 0.01 μF capacitor’s
reactance. Normally, for factional horse-power reactive
loads, the resistor found in the snubber circuit will
have a power rating from 1/2 W to 2 W. The resistor
should be a low inductance type to adequately filter
the high frequency transients.