Re: MOSFET answer

On Thu, 01 Jun 2006 20:01:45 GMT, the renowned Joerg
<notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote:

Hello Spehro,


Answering my own question about a TO-220 MOSFET that switches on solidly
with 2.7 volts on the gate, the answer appears to be IRF3708.

This stuff is quite difficult to search. MOSFETs are one of those
components that's just exploding in options, and the parametric
searches often give you Rds(on) without telling you the Vgs for that
parameter. Many of the most attractive newer options (especially the
newer packages) turn out to be will-o'-the-wisp fata morgana parts
which are unavailable in small quantities.


It's also important to rely on guaranteed data and for Rdson at a
certain Vgs that would be the "max" column. I have seen many designs
where people just took the graph. Worked fine initially. Then another
batch arrived and it was like popcorn.

Of course. Fortunately there are more and more that are guaranteed to
have a certain Rds at 2.5V or even 1.8V. Unfortunately, that usually
goes along with a low breakdown voltage (I've seen as low as 8V, so
the D-S might break down before the gate). Still, the latter provides
a clue for searching, which will help until the people designing the
parametric searches get a clue and make it possible to search for what
you need.

Quite a few devices that are marketed as logic level are too marginal
for my taste.

4.5V ratings are usually safe enough with a 5V supply, assuming a
solid CMOS drive, but not with a 3.3V supply, or with BJT emitter
followers ( a resistor from (CMOS) input to output with the latter can
help with slow switching).


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@xxxxxxxxxxxx Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
.

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