Rule of thumb for replacing power transistors with MOSFets?...

[John Robertson]

On 2023/03/17 9:41 a.m., John Robertson wrote:

On 2023/03/16 12:15 a.m., Jan Panteltje wrote:
On a sunny day (Wed, 15 Mar 2023 12:00:02 -0700) it happened John
Robertson
jrr@flippers.com> wrote in <tut4jn$10ok6$1@dont-email.me>:

I\'m updating some game board designs and was curious if there is any
sort of printed guideline for replacing silicon driver transistors with
MOS? Both NPN and PNP.

For example TIP122 Darlington transistors driven by another pre-driver,
that is the TTL interface. I\'ve seen many a substitute, but would like
to have the theory explained so I can make better use of it and
understand exactly what I am doing.

A good reference book you can recommend perhaps? Books and I usually get
along very well.

Too many projects and not enough to hunt down all the solutions!

Thanks, and sorry for the on-topic post...

John :-#)#

This is how MOSFETs work:
https://en.wikipedia.org/wiki/MOSFET


If you want to use one: there are basically 2 types: some conduct with
zero volts at the gate
and some do not conduct with zero volts at the gate.

To interface with 5V logic I usually use an IRFZ44A MOSFET (off when
0V at the gate).
10 for $8.63 on ebay..
  https://www.ebay.com/itm/324380901727
even cheaper at other places
datasheet:
  https://datasheetspdf.com/pdf-file/799031/Samsung/IRFZ44A/1

look at page 3 figure 2 for at what voltage the thing starts conducting.

At 5 V from TTL logic it can do several amps.
MOSFETS do not pose a current drain on the driver (very high
impedance, these should work for a pinball machine I\'d think).
Also these MOSFETS have a reverse diode that limits the peak voltages
when switching an inductive load,
see figure 13 in that datasheet (may save you a protection diode, but
of course you can leave it in too).

So this is a \"simple practicle man\'s few lines book\" but you gotta
start somewhere...

More in my book \'The Fart Of Electronics\' provided I ever can find a
decent pen to write it.

There also exists a book \'The art of electronics\' I\'v never read it
but people get all exited about it it seems.
The author used to post here...

I\'ve been meaning to buy Winfield (& Horowitz)\'s book for a while, and
now you have tipped the balance. I\'m sure that will be a useful addition
to my library!

Thanks!

John :-#)#

Ordered the hard cover - 2015 3rd edition - (I prefer books) and also
picked up the PDF from Academia.edu.

Wow! What can I say other than this is the book I\'ve needed my whole
career! To say it goes into detail but in plain enough language for a
non formally (EET) student like me to understand.

Now I think I will have to get the X Chapters (2020) that Winfield spoke
of here, after reading the 3rd edition first.

I\'m sorry Mr. Hill no longer posts here, he was a great reference and I
think he enjoyed interacting with the folks here that are actually
interested in learning about electronics and sharing their knowledge.

John :-#)#

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