Transistor heating up

Three comments:

1.  A single 2222 may be a little weak for this application.  With 1K base resistor you're getting 4 mA current from base to emitter, which the transistor amplifies by a factor of 40 or so resulting in 160mA, which is less than the 200mA required by the fan.  So you might want to reduce 1K down to 750 or so to get more margin.  I don't know how much current the Arduino can source: see what voltage you are actually getting at the Arduino pin.  If it can't source much current, try a Darlington pair instead of a single NPN transistor: http://en.wikipedia.org/wiki/Darlington_transistor

A Darlington pair has two stages of current boost, so you can use a very small current to switch a very large current.

2.  You need a Flyback Diode: http://en.wikipedia.org/wiki/Flyback_diode

Let's say you've successfully turned on the fan with the transistor.  The fan is an inductor with 200 mA or so running through it.  Inductors cannot change current flow instantaneously.  When you turn off the transistor, the current has to go somewhere so it charges up the stray capacitance at the transistor's collector to a really high voltage, which shorts out your transistor.  If you've been burning through transistors, this is why.

The flyback diode goes across the motor from NPN collector to your +16V supply.  When the transistor shuts off and the collector voltage starts to rise, the flyback diode switches on and provides a safe place for the motor's current to go.

3.  IMO you don't need a collector resistor.  The fan motor provides enough of a voltage drop.

Three comments:

1.  A single 2222 may be a little weak for this application.  With 1K base resistor you're getting 4 mA current from base to emitter, which the transistor amplifies by a factor of 40 or so resulting in 160mA, which is less than the 200mA required by the fan.  So you might want to reduce 1K down to 750 or so to get more margin.  I don't know how much current the Arduino can source: see what voltage you are actually getting at the Arduino pin.  If it can't source much current, try a Darlington pair instead of a single NPN transistor: http://en.wikipedia.org/wiki/Darlington_transistor

A Darlington pair has two stages of current boost, so you can use a very small current to switch a very large current.

2.  You need a Flyback Diode: http://en.wikipedia.org/wiki/Flyback_diode

Let's say you've successfully turned on the fan with the transistor.  The fan is an inductor with 200 mA or so running through it.  Inductors cannot change current flow instantaneously.  When you turn off the transistor, the current has to go somewhere so it charges up the stray capacitance at the transistor's collector to a really high voltage, which shorts out your transistor.  If you've been burning through transistors, this is why.

The flyback diode goes across the motor from NPN collector to your +16V supply.  When the transistor shuts off and the collector voltage starts to rise, the flyback diode switches on and provides a safe place for the motor's current to go.

3.  IMO you don't need a collector resistor.  The fan motor provides enough of a voltage drop.

Just got home and started to play with the toys.

Thanks for the replies you guys. Newbie mistake. The NPN transistor was plugged in backwards.. It was drawing current onto itself and was heating up. Thanks for the insights though.

John Beetem wrote:

 

Three comments:

 

1.  A single 2222 may be a little weak for this application.  With 1K base resistor you're getting 4 mA current from base to emitter, which the transistor amplifies by a factor of 40 or so resulting in 160mA, which is less than the 200mA required by the fan.  So you might want to reduce 1K down to 750 or so to get more margin.  I don't know how much current the Arduino can source: see what voltage you are actually getting at the Arduino pin.  If it can't source much current, try a Darlington pair instead of a single NPN transistor: http://en.wikipedia.org/wiki/Darlington_transistor

A Darlington pair has two stages of current boost, so you can use a very small current to switch a very large current.

 

Regarding the 1k resistor. I believe the datasheets stated current gain of min 150 and max 300 for Ic = 150mA which the fan actually stated .16A. That was bad on my part.

Thanks for such great feedback though. You live and you learn. I am so glad I found this community.