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Paralleling ULN2803 transistors

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Grant Fair

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Jun 19, 2001, 5:03:55 PM6/19/01
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Can I parallel the darlington transistors in the ULN2803 by soldering
one chip piggyback onto the same pins on the chip below?

Grant

Frank Bemelman

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Jun 19, 2001, 6:19:18 PM6/19/01
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Grant Fair <grant...@sympatico.ca> schreef in berichtnieuws 3B2FBE3B...@sympatico.ca...

> Can I parallel the darlington transistors in the ULN2803 by soldering
> one chip piggyback onto the same pins on the chip below?

Sure, but the maximum current handling will be less
than the expected(?) factor 2.

I recall a pin-compatible version that used fets with
low rds-on. Forgot the number. Might be worthwhile
to look into.


--
Frank Bemelman
(to email, remove 'x')


Grant Fair

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Jun 19, 2001, 8:23:46 PM6/19/01
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Frank Bemelman wrote:
>
> Grant Fair <grant...@sympatico.ca> schreef in berichtnieuws 3B2FBE3B...@sympatico.ca...
> > Can I parallel the darlington transistors in the ULN2803 by soldering
> > one chip piggyback onto the same pins on the chip below?
>
> Sure, but the maximum current handling will be less
> than the expected(?) factor 2.

I tried it just placing one on the top of the other while driving a
stepper. Both got warm, so I assume they both were working. I only need
1.6 amps per output, and the original design parallels two darlington's
per coil output. Guess I should try measuring the current.

> I recall a pin-compatible version that used fets with
> low rds-on. Forgot the number. Might be worthwhile
> to look into.

Will do, great idea if it exists. Any more info, such as the
manufacturer?

> Frank Bemelman
> (to email, remove 'x')

Many thanks,
Grant

Frank Bemelman

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Jun 20, 2001, 11:52:11 AM6/20/01
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Grant Fair <grant...@sympatico.ca> schreef in berichtnieuws 3B2FED12...@sympatico.ca...

> Frank Bemelman wrote:
> >
> > I recall a pin-compatible version that used fets with
> > low rds-on. Forgot the number. Might be worthwhile
> > to look into.
>
> Will do, great idea if it exists. Any more info, such as the
> manufacturer?

It was the TPIC2701 by Texas, but I was mistaken, this is a
driver with only 7 outputs, replacement for uln200x types.

--

Mike Page

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Jun 20, 2001, 4:59:16 PM6/20/01
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Grant Fair wrote:

The problem with this sort of darlington package is that the switch when ON is still around 0.7 to
1.0 volts. If power dissipation is a problem, consider using FETs, or rolling your own darlingtons,
with the collector of the first transistor connected to V+, whatever that is. That allows the second
transistor to properly saturate. I have seen some tasty FET packs - two per package I think but
small, juicy, and cheap.

Best Regards,
Mike.
===========================================================
Mike Page mi...@eclectic-web.co.uk
BEng(Hons) AMIEE www.eclectic-web.co.uk

Make it idiot proof and someone will make a better idiot.
- anonymous

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