need help with the terminology behind resistors (im new!)

[evilcow]

Okay. I have a vague post before under "electronics =\". I'm basically going to rephrase the whole question. I'm asking for what kind of resistor (ohms) do i need? Here are the specs for the load on the circuit. It's pretty small and simple.

-> I've got a 12.38V powersupply (alternates from 12.38V to 12.37V) Ofcourse this is DC.

-> Now the first load is a LED that requires 25mA & 6V.

-> My switch can handle upto 12A / 125V's (just wanted to let ya know!).

-> Lastly my fan requires 12V (not sure about how many mAs).


I need to know what kind of resistor i need to use to powerdown from 12V to 6V. Basically trying to halve the voltage.

 

[phalanx]

okay, here's how it works.
You place a resistor of 470 Ohm in series with the LED, then you place that circuit parallel over your fan.
Put the switch in series with the fan and voila.

You see, the LED has a forward voltage of approx. 2 V depending on the colour (doesn't really mather much), so that leaves 10.38 V over the resistor. To get a current of 25 mA you'd need a 417 ohm resistor which doesn't exist, the closest higher one to that is a 470 ohm one. That leaves you with 22 mA which is more than enough for any LED.

The fan will draw something of a 150 - 200 mA but that doesn't affect the LED at all, since they are parallel and the current through every branch of a parallel circuit is totally independent of the other ones. Your switch will have to switch the current that goes into the fan AND the current of the LED but that shouldn't be a problem with a 12A switch.

 

[evilcow]

i love you! THX haewohaeohea =)