PISO-P8R8U/P16R16U/PEX-P8R8i/P16R16i User Manual (Ver.1.6,Mar/2010, PMH-021-16) -
17
-
I
f =
2 mA ~ 20 mA
As a rough estimate:
If Vin = 120 V and the photo-coupler turn-on voltage is ignored,
the result is:
Vin /
I
f = Ri
Vin
=
120(V),
I
f
=10(mA), Ri = Vin/
I
f
120(V) / 0.01 (A) = 12000 (
Ω
)
If the resistor Ri is replaced as 1.2 K
Ω
, the power consumption of Ri can be
calculated as follows:
P = I
2
Rex = (10 mA)
2
* 1.2K
Ω
= 1.2 W
The power consumption is 1.2 Watts, but selecting 1.5 or 2 Watts is better.
Thus, a 1.2 K / 2 W resistor can be selected to replace the resistor Ri.