Connect VGA cooling fan (12vdc - 0.1A) to constant current driver (120Vac to 12- 22vdc @ 0.3A)
If you hooked the fan directly to the constant-current driver, it would raise the voltage until it got to its compliance limit (22 V), which would seriously overpower the fan. What can you do with resistors?


You could use a series resistor as a voltage dropper. It would have to be (22 V - 12 V) / 0.1 A = 100 &Omega;, and will be dissipating 1 W. This works as long as the 22 V is a fairly firm limit &mdash; it may or may not be.
You could use a shunt resistor to bypass the excess current. It would have to be 12 V / 0.2 A = 60 &Omega;, dissipating 2.4 W.


Neither of these seems particularly desirable. Get a 12 V power supply for the fan.