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bigmik

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Joined: 20/06/2011
Location: Australia
Posts: 2950

Posted: 07:03am 01 Jun 2022

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Hi All,

I have been around Bipolar transistors for way too long (going back to the BC108 and OC-71 varieties). I think it is time I stepped over the bridge into the world of MosFets.

I am looking at having a play with them and I am after suggestions for good ones to use for 3.3v circuits.

I am also mainly looking for SMD SOT-23-3 but I wouldn't mind a couple of suggestions for To-92 variety.

I am leaning towards towards 2N7002 for N-Ch and I have a few A19T P-Ch that I used in the Silicon Chip Pico-Pi backpack that seemed to work but I want any suggestions for a decent general purpose P-Ch suggestion.

So My questions are, What general purpose N-ch an P-ch Mosfets should I look for 3.3V circuits in BOTH sot23-3? And also To-92 packages?

Thanks in advance,

Kind Regards,

Mick

Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<<

CaptainBoing

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Joined: 07/09/2016
Location: United Kingdom
Posts: 2170

Posted: 08:01am 01 Jun 2022

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here are my standard go-to's:

FQP30N06L N-CHANNEL. 60V, 32A. Vgsth 1-2.5V, 35-45mR Rds. TO 220
FQP47P06 P-CHANNEL MOSFET - I use a lot in reverse-polarity protection
SI2300 N-CHANNEL FET 30V 3.3V LEVELS 3.6A SOT23

h

Volhout
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Joined: 05/03/2018
Location: Netherlands
Posts: 5091

Posted: 08:30am 01 Jun 2022

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Hi Mick,

There is such a variety it is hard to suggest.

For logic level I always turn to BSS138 N channel with Vth of 1.8V.
The 2N7002 is similar but has a higher Vth (2.5V) which in some cases over temperature may not turn ON reliable from 3.3V

Volhout

PicomiteVGA PETSCII ROBOTS

bigmik

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Joined: 20/06/2011
Location: Australia
Posts: 2950

Posted: 12:11pm 01 Jun 2022

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Thank you CapnBoing, Volhoult,

I was thinking (for further down the track in my experimenting) of TO-220 types as well, initially I was looking for small SOT23-3 types and closely followed by TO-92 types.

I know it�s hard to specify a good all round choice of mosfet as every situation is different.

I know with bipolar I would immediately say BC548 and BC558 so I was hoping there were similar general purpose ones in the misfit family.

I will take all your suggestions to task and possibly build up a small collection.

Thank you again,

Regards,

Mick

Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<<

palcal

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Joined: 12/10/2011
Location: Australia
Posts: 1993

Posted: 08:17pm 02 Jun 2022

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Still have an OC70 in my parts drawer, from an AWA radio about 1960.

"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"

Volhout
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Joined: 05/03/2018
Location: Netherlands
Posts: 5091

Posted: 05:42am 03 Jun 2022

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Scratch away the black paint and they make great photosensors. Had a whole family of those black glass tubes. OA47, OC44, OC45, OC70, OC71, OC72, and metal, the heavier stuff OC16.

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Mixtel90

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Joined: 05/10/2019
Location: United Kingdom
Posts: 7937

Posted: 06:14am 03 Jun 2022

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Then they caught on and started filling the tube with jelly that made it a much more difficult process. File the glass round the base, carefully snap the tube off, clean the gunk off the junction with meths and reassemble with glue round the base. Still not quite as good as an OCP71, but a lot cheaper. :)

It's a lot cheaper to buy modern optical sensors than NOS OC71s now, and they work a lot better.

If you saw the can off an OC35 and clean the thermal paste out those are often a bit light sensitive too - but rather bulky. I still have an old TO35 case that has been completely cleaned out, including the pin holes, and now makes *the best* template for marking hole positions and outlines on heatsinks.

Mick

Zilog Inside! nascom.info for Nascom & Gemini
Preliminary MMBasic docs & my PCB designs

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