Technical question on Fets and MOSFETS...

[orange_glow_fan]

 In an effort to increase current handling abilities, a 'friend' suggest that one could connect a fet or mosfet in parallel with another identical device....

I tried to wrap my mind around that, but my limited knowledge pretty  much put a stop to that...In theory it sounds possible, yet somehow it seems wrong...


How's that for indecision....

What say you?

Thanks,

Kerry

[orange_glow_fan]

P.S. it would probably help if I mentioned what this is doing.. the mosfet is controlling a brushed, DC motor in a small quadcopter.

[Terry S]

Yes, you can put FETs in parallel -- a technique I've used many times for motor controls. There are things you need to keep in mind, such as being sure to use identical parts, and keep them at the same thermal potential. You also need to understand the gate drive requirements that can change dramatically when you put FETs in parallel.... and that the PCB layout is critical, keeping traces identical and sized properly. Most of this is learned from many years of experience and trial and error, and not well discussed in technical literature. Well, it wasn't when I was learning it....

Terry

[NeonJohn]

With FETs, it works naturally, as the conduction channel has a positive
temco. The cooler FET has the lowest resistance and so it takes more of
the load until it reaches the temperature of the others.

IGBTs have a negative tempco EXCEPT for those designed to be run in
parallel. In my highest power induction heaters, I have three 900 volt,
30 amp IGBTs in parallel on each side of the Royer oscillator. One key
to making it work is to have the devices tightly thermally coupled so
they all see the same temperature.

John

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[gregebert]

However, for nixies you wont encounter enough load-current that would require paralleling of devices.

Here's a tech paper, albeit old, that describes paralleling of MOSFETs in detail. It was written by my college prof back in the 1980's. At that time, there were far fewer choices for devices.

http://www.infineon.com/dgdl/para.pdf?fileId=5546d462533600a401535744b4583f79