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[on:]

Hello All,

I am new to electronics and the Arduino. I am trying to determine what would be the correct diode to use to restrict the reverse current flow for my fan, here is my setup.

ARDUINO PIN OUT ----> 1K resistor to the base of ----> NPN 2SD313 Transistor ----> Archer RS4005 1 amp 600V diode (only one I had lying around that seemed suitable) between collector and emitter. Power source to fan is a PC DC 12V 3AMP. The fan is a 12V 0.23A. Fan ground to Transistor Collector. Transistor Emitter to ground. They all share a common ground. Sorry for no diagram.

Everything to me seems to work fine. I'm not sure i'm using the correct Diode.

Thanks for your assistance.

[Reply #1 on:]

Diode goes across the inductive load (fan) not across the transistor.  Diode goes for +12 to Collector, same as the fan.  Make sure the Cathode (negative) side goes to +12 and the Anode (positive) side goes to the Collector.

[Reply #2 on:]

Look at the setup as so.

[Reply #3 on:]

Thanks for the reply. I guess i'm even asking myself more questions now. I find a lot of similar setups such as this one I've attached. What is this accomplishing?

[Reply #4 on:]

Thanks for the reply. I guess i'm even asking myself more questions now. I find a lot of similar setups such as this one I've attached. What is this accomplishing?

Note: the TIP120 aready has a diode from the Collector to the emitter. See:  http://www.adafruit.com/datasheets/TIP120.pdf

Diode goes across the inductive load (fan) not across the transistor.  Diode goes for +12 to Collector, same as the fan.  Make sure the Cathode (negative) side goes to +12 and the Anode (positive) side goes to the Collector.

He has said what you should do.
See: http://en.wikipedia.org/wiki/Flyback_diode

[Reply #5 on:]

You also might want to add a capacitor parallel to the fan as well. It just to smooth out the signal.