Triacs and
AC switches insulated control
UM2027
30/37
DocID029048 Rev 1
the NPN transistor collector-emitter, I
GT
the TRIAC gate current and V
GT
is the TRIAC gate
triggering voltage.
The collector resistor (R
18
) of the NPN transistor is defined in the next equation, with R40
being the NPN transistor resistor filter, VCC_AC the power supply to provide the gate
current to the AC switch, VCE(SAT)
Opto
the transistor collector-emitter of the optocoupler,
I
GT
the TRIAC gate current, ß
NPN
is the NPN transistor gain and VBE(SAT)
NPN
is the NPN
transistor base-emitter.
Given the optocoupler and the R
28
resistor value, the LED resistor R
29
of the optocoupler is
defined by the equation below.
in our example, with the IS127 optocoupler and the 2N2222 NPN transistor, the following
resistor values should therefore be chosen.
