On Fri, 27 May 2011 18:00:45 +0100, "Ian Field" wrote:


"Grant" wrote in message
.. .
On Wed, 25 May 2011 18:12:11 +0100, "Ian Field"
wrote:


"John Larkin" wrote in
message
...
On Mon, 23 May 2011 16:35:57 -0700, Tim Wescott
wrote:

On 05/23/2011 03:52 PM, Jim Thompson wrote:
Is this the correct pin out for a 2N7000...

http://analog-innovations.com/SED/2N...ak_Pin_Out.pdf

My expectations, from bipolar's, would be, facing the flat, leads
down. left-to-right...

D-G-S

My expectations, from browsing many data sheets, is that the pinout of
any three-terminal device is pretty well standardized:

Pin 1: random
Pin 2: random
Pin 3: random

Even the pin numbers can be random. I've seen all possible
permutations of 1-2-3 on various SOT23 parts. We use the "Motorola"
convention, and force any parts that we use into it.


So, maybe the 2N7000 is a little randomer than you thought -- it's still
normal.

All you need is a ohmmeter to discover/verify the pinout.


What I use is a Steinel continuity checker, it has a 12V keyfob battery &
2
LEDs. Stick the + probe on the drain and the - on source, usually stray
charge will cause enough conduction to make the LED glow, breifly moving
the - probe to gate discharges it then back to source and no light means
good MOSFET, move the positive to the gate to charge it and it conducts
again.

With unknown leadouts its relatively simple to identify the gate as
there's
no continuity to either other terminal either way round. Which way round
the
body diode is tells you half of what else you need to know.

A decent meter identifies the body diode by voltage drop, not continuity.

Meter I'm using here is half the price I paid for decent test leads for it


So knowing which two pins hold the body diode unambiguously identify the
three pins for me.


About half the time there will be enough stray charge on the gate to make it
difficult to tell between diode & channel conduction - at some point you'll
have to guess the channel polarity and precharge the gate capacitance with
the right polarity to cause channel cutoff.

No, because when I 'short' all pins together in my fingers, the gate is
discharged, I've never met a MOSFET turned on during simple metering.

Its a quicker route to find out which pin doesnt continuity to anywhere,
then figure out which polarity there turns what's between the other 2 pins
into a 1 way street.

You do it your way, I do my way -- I'm trust measurement methods I use
because they work reliably, because if I get a funny result, I repeat
until I get a proper result or decide the part is blown. You don't seem
to realise the value of measuring the body diode forward drop voltage,
use a decent DVM with a diode range and there's no ambiguity.


Only time I've been caught out recently is when I tested a three lead
TO220 device and all pins open circuit to each other -- lookup the part
number and it's an IGBT, I have no idea how one tests them! I imagine
there's an argument for turning the gate on with them, since there's
no body diode to discover. How to safely do that in=circuit?

Grant.