Advantech MIC-3723 User Manual page 39

Where
VS: Power supply voltage of current sink.
RL: Load of current sink.
PD: Power dissipation of FET.
When you determine VS and RL, three conditions must be satisfied.
VS > (RL + 251) ( 0.02)
PD = (VS - (RL + 251) * 0.02) * 0.02 < 0.2
Example 1
If you use the internal power supply VS = +12 V,
RL must be less than 349 W. (12 / 0.02 - 251 > RL).
Select RL = 200, PD = 0.0696 < 0.2 OK!
Example 2
If you use the external power supply VS = +40 V,
RL must be less than 1.75 kW (40 / 0.02 - 251 > RL).
Select RL = 200 W, PD = 0.62 > 0.2 fail!
Reselect RL = 1 kW, PD = 0.3 > 0.2 fail!
Reselect RL = 1.5 kW, PD = 0.1 < 0.2 OK!
33 Chapter 3