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'[EE]:: Jelly Bean Mosfets'
2007\02\21@054302 by Russell McMahon

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(re)tagged
> Subject: Jelly Bean Mosfets

> I'm wondering what types all purpose n&p fets I should keep on hand.
> Ones
> that have a wide range of uses and are inexpensive and easy to
> obtain.  What
> to you keep in your kit?
>
> I have two applications where I may need a low voltage drop
> transistor.  One
> is for around 10A @ 5 or 12volts and the other is 50mA @ 6 volts.
> In the
> second case (50mA) I would like the gate voltage to be logic level.
>
> How sensitive are these mosfets to static?  How easy is it to blow
> them
> before I get them installed?

"What you can get cheaply locally that works for you and meets your
needs" :-)
ie there are a vast number of types and availability varies with where
you are.
Buy what you can get that suits.

Through hole:        I try to keep a tube or so of highish current
grunty package lowish voltage N channel devices (eg the beautiful
TO247 IRFP250), something a bit less grunty in P Channel with similar
voltage ratings and some 200V and 500V plus N Channel parts in TO220.
P Channel I usually aim to have only up to 200V as above that they get
rare and dear. Also, HV P channel tend to have nastily high Rdson
unless you pay vast amounts for them and maybe even then. I'd use an N
channel where I could for one off jobs as they are usually cheaper per
spec. I also have a few lowish voltage TO220 N Channel "logic" FETS
(ie Vgson < 5V for high degree of enhancement) for logic switching,
BUT even non logic parts are often usefully enhanced at Vg=5V as long
as current to switch is not too high. I seldom use smaller than TO220
parts as they are often not substantially cheaper and are less useful
overall.

Once you start into surface mount it's a whole other world ...


> How sensitive are these mosfets to static?  How easy is it to blow
> them
> before I get them installed?

Nowadays gate protection is usually reasonable and you tend not to
find devices mysteriously dying as long as you are sensible. Even
handling without wrist straps and earthing doesn't yield too many
failures, but if you care you should take a little effort. I about
never have a gate failure during installation and I'm sensible but not
ultra paranoid with handling.

Adding a zener gate to source close to the FET can help prevent quite
unexpected failures due to eg Miller effect coupling to the gate
during switching or high frequency ringing. Some say that a zener
there can cause more problems than it helps but I have used them often
with no problems. The excessively dedicated may add a reverse biased
gate-drain Schottky.


       Russell



2007\02\21@061254 by Wouter van Ooijen

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> > I'm wondering what types all purpose n&p fets I should keep
> on hand.
> > Ones
> > that have a wide range of uses and are inexpensive and easy to
> > obtain.  What
> > to you keep in your kit?

what is your use?
- audio / analog
- HF
- low-power switching
- high-power low-voltage switching
- high-power high-voltage switching
- etc

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2007\02\21@094425 by Gordon Williams

picon face

----- Original Message -----
From: "Wouter van Ooijen" <spam_OUTwouterTakeThisOuTspamvoti.nl>

{Quote hidden}

My original question (long ago) included:
...
I have two applications where I may need a low voltage drop transistor.  One
is for around 10A @ 5 or 12volts and the other is 50mA @ 6 volts.  In the
second case (50mA) I would like the gate voltage to be logic level.
...

There seems to be many different ones out there and I was looking for
something in a TO92 package for breadboarding that had an equivalent in a
SMT package for the 50 mA application.  A TO220 package or something similar
would be good for the 10 A application.

I have never used MOSFETs before and I was looking for something cheap and
dirty and robust enough that I'm not going to zap it by looking at it, which
I understand can happen.

Regards,

Gordon Williams


2007\02\21@100337 by David VanHorn

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>
> Adding a zener gate to source close to the FET can help prevent quite
> unexpected failures due to eg Miller effect coupling to the gate
> during switching or high frequency ringing. Some say that a zener
> there can cause more problems than it helps but I have used them often
> with no problems. The excessively dedicated may add a reverse biased
> gate-drain Schottky.


Popping the gate bond wires with too much drive current is always good for a
laugh.

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