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Hi everyone, hopefully someone can give me a quick trouble free answer.

I would like to know which transistor I require?

The signal is a pwm pulse of about 300hz from the arduino (244.4hz i think) obviously at 5v. I would like this to be at 12v though?

Can anyone help me? Also how would I wire it up? PWM pulse to Base, and then would it be 12v to collector and the 12v pwm would be output from the emitter?

Thanks.
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Here is a circuit for a fan controller that shows one way to wire it up:

http://ruggedcircuits.com/html/circuit__7.html

This design uses a MOSFET transistor (drain/gate/source), though you could also use a BJT (collector/base/emitter).

An important question is what you are doing with the 12V PWM signal. Will it be required to supply/sink a lot of current? If it is not an inductive load then you can omit diode D1 in the circuit.

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What I am using the PWM for worked fine connected directly to the arduino using 5v but its supposed to work with 12v so it worked using whatever current the arduino can supply so very minial I believe.
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So you are switching less than 40mA?

Pretty much _any_ small-signal NPN transistor will do that job (or a logic-level n-channel MOSFET).   For NPN you must use common-emitter configuration, not the emitter-follower you initially describe (which has no voltage gain!)

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add 2nd stage if you 12V out to follow 5V in (high for high, low for low)
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Quick google searched turned up:



So I'd use this setup but with a 1kohm resister between the arduino and the base? And what value would the resisitor be between the output at the collector and +12v be? around 1k again?
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RE not needed.
RC 1K would be fine, gives ~10mA thru Rc to for driving the next stage high.
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Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

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