Hey guys. Wondering if some fancies throwing their two pence worth in.
I'm trying to control the fans in an old xbox 360 chassis without much luck, mainly because I like learning the hard way.
Eventually I want the fans temperature controlled through PWM.
I'm fairly new to electronics so please forgive me if my knowledge is lacking.
The fans are rated at 12v 0.4A.
I am using a 12v 60w 5A LED power supply inside the chassis to power the fans, arduino, raspberry pi and network switch.
I was trying to use a BC547 to control the fans, well burnt a couple of those fairly quickly before reading datasheet and realising I was trying to send too much current for it.
So, I have some IRFZ44N and IRF3205, can I use either of those with the BC547 to make a darlington transistor to control the fans, or do I need to order one??
Darlingtons are for BJT's - they are essentially obsolete technology. Modern logic level MOSFETs are what you want - unfortunately the two MOSFETs you have aren't really spec'ed for use with 5v on the gate - though the IRF3205 would probably work well enough, from the looks of the datasheet.
Just search digikey/etc for a "logic level" mosfet (this is a feature you can filter the search by on these sites), and find one that comes in a package you won't mind soldering to, with a current rating well above what you need.
I'm not expecting this project to produce too much heat so I'm not convinced the fans will run that much, therefore probably work well enough would do, will be good enough for this. Can I use the 3205 straight up or will I need the BC547 controlling it??
I would try using the 3205 straight up. Using another transistor to control it will not work very well, because your problem is getting the gate voltage high enough, not getting current through it. There are a couple of schemes I can think of to use one of those and get better performance from it - but all of them are harder than just buying logic level fets in the first place, as others have suggested.
But yeah, the datasheet suggests that you should be able to get away with the 3205. Gate through 100 ohm resistor to Arduino pin, source to ground, drain to the - side of the fan. Higher value resistors are okay - the 220 ohm ones that everyone has on hand for driving LEDs are fine. (but - this only works because the fet turns on at a somewhat lower voltage than most non-logic level fets, and is rated for many times the current the fan uses - in general, the fet is inappropriate for use with the Arduino)
Long term, you should buy a stock of decent logic level FETs. (as an aside, I happen to sell some small logic level fets that work as low as 1.8v on the gate, pre-mounted on breakout boards because they don't make low voltage fets in through-hole packages - but you only need a normal logic level (4.5v) fet, not the lower voltage ones - so stand-alone through-hole fets that will work for you are readily available )
4-pin fans can be powered straight off 12v and the speed controlled with logic level PWM on the PWM pin, without - they have the circuitry internally to deal with that (that's the point of that fourth pin).
Non logic-level MOSFETs are designed for 12V of gate drive, 10V minimum.
Most logic level MOSFETs are designed for 5V of gate drive, 4.5V minimum, that's the sort to use from 5V
Using a non logic-level MOSFET at 5V isn't a good idea - switching is at best incomplete, very slow,
you might as well use a darlington it will probably perform better.
