Figure 42.
ACST310-8B datasheet extract
At 0 °C ambient temperature, I
GT
* 1.4 = 14 mA is required to ensure Triac activation. Gate-cathode resistor (R
GK
= R110) current should be considered in the calculation as it is significant. In this case, the required I
G
is:
IG min =
VGT
R110 + 14 mA =
1.1
220 + 14 mA = 19 mA
Considering this current value and the VCC_AC minimum voltage, the gate resistor calculation is:
R106 + R107 =
V R106 + R107
IG min
=
VCC_AC min + VGT max − VCEsat
IG min
= 13 + 1.1 − 0.3
19 × 10−3
= 726 Ω
The nearest normalized value is 374 Ω.
You can calculate maximum power in the resistors considering VCC_AC maximum voltage:
IG max =
V R106 + R107
R106 + R107 =
VCC_AC min + VGT max − VCEsat
R106 + R107
= 21 + 1.1 − 0.3
748
= 29 mA
PR106 = R106 × IG max
2
= 0.31 W
Therefore, R106 and R107 are 374 Ω/0.5 W resistors.
Note:
Use the above formulas to recalculate resistor values in case of schematic use in another design with a different
ambient temperature.
X103 AC switch
X103 is an ACS108-8TN AC switch. The figure below gives the I
GT
parameter value and its variation against
temperature.
Figure 43.
ACS108-8TN datasheet extract
At 0 °C ambient temperature, I
GT
* 1.6 = 8 mA is required to ensure Triac activation. Gate-cathode resistor (R
GK
=
R111) current should be considered in the calculation as it is significant. In this case, the required I
G
is:
UM2304
AC switch gate control dimensioning
UM2304
-
Rev 3
page 36/46
