Quote9v 30mAI thought you were 0.006 wire that needed 400mA?
I can't open that link.Are you connecting the wires in series or in parallel?The transistor will also have a voltage drop across it, probably approaching 2V with 400 or 800mA. You need to adust your resistor to account for that:(12V - 2V)/.4A = 25 ohm - 15.6 ohm = 10 ohm resistor.Presistor = I^2*R = 0.4 * 0.4 * 10 = 1.6W, so at least a 2W rated resistor.
Oh, that diagram is just wrong! If you are wired like that, you have to fix that before proceeding.http://www.fairchildsemi.com/ds/TI/TIP122.pdfProblem is TIP120 is not a straight NPN transistor - it is 2 NPN connected in Darlington fashion, where 1st NPN provides extra drive to the 2nd for higher Collector-Emitter current flow. The drawback is higher Collector-Emitter voltage drop, closer to 2V than say 0.5 or 0.7V.That may work out okay here tho:(5V - 2V)/(7.8 ohm) = 384mA.If the 5V is something else, re-do the math and add the appropriate current limit resistor.
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