Mosfet As A Switch For Inductive Load

I agree. I always use a diode. I've always assumed the built-in diode is more for parasitic inductances than for large coils.

No prob...
But you are not entirely dissagreeing with me...(see first word of my original post)

I did say for small inductive loads example a small DC motor (12v @1A) which will typically give say 3 times the rail as a reverse spike, which is well within the rating of say a 14N05L.
Measurement with a scope is always the best way to see what's going on, and if the spikes are well withing the MOSFET rating then there is no prob.
But better safe than sorry is a good thing, which I meant to be the essence of my reply.
Out of interest isn't it better to place the diode on the actual load as it reduces the current path and thus radiation?

(The position of my comma in line 2 of my original post is incorrect, here are some spares which can be used elsewhere,,,,,,,,,,,,,,,,,,,)
Del

Thanks for all reply...

If the mosfets are used for BLDC motor control, then what is recomended in this case as far as external frewheeling diodes concerns?

<Sigh> if only I knew what BLDC stood for...
Anyhow I think the concensus has been pretty firmy established as, when in doubt fit 'em.

Actually there is a good link in this blog which I wrote a while back about flywheel diodes in DC motor control.
Del

BLDC = Brushless DC motor which generally requires in 3 phase control

Maybe here can help further:-

http://www.embedded.com/columns/technicalinsights/222600637?_requestid=201287

The answer to the question will depend on several items. Without knowing the FET characteristics it would be safest to install a clamping diode.

Many newer FETs can reliably switch an un-clamped inductive load. The ability of the FET can be determined by the Eas specification of the FET. This is the Single Pulse Avalanche Energy rating of the FET. For example the Fairchild FQA24N50 has a rating of 1100 mJ. Knowing the inductance and the current and the duty cycle you will be switching will allow the determination of whether this device can reliably switch your load without an external clamp.

Be careful since not all FET manufacturers will have a high Avalanche Energy rating.

If there's a distance of several inches or so between the FET and the inductive load, you may want to clamp physically at the inductor. Once you open space between the FET and the inductive load you'll have interesting currents flowing through the ground plane that can mess up a control IC, etc. In design reviews I've experienced, the clamp at the inductor would be a requirement.