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July 2001

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Subject:
From:
"Nagel, Michael" <[log in to unmask]>
Reply To:
DesignerCouncil E-Mail Forum.
Date:
Tue, 31 Jul 2001 10:09:38 +0200
Content-Type:
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text/plain (79 lines)
Hello David!

For currents if that magnitude nobody seems to think about IGBTs.
They are quite OK, even for high voltages and switching frequencies
up ~20kHz AFAIK.

Best regards,
        Michael Nagel


-----Original Message-----
From: David Cary [mailto:[log in to unmask]]
Sent: Donnerstag, 26. Juli 2001 23:18
To: [log in to unmask]
Subject: [DC] high-current relay


Dear Designer Council,

I'm working on a project where I need to switch a little over 60 A of
current.

I know I could just put lots of MOSFET transistors in parallel, and they
will
share the current. Just like light bulbs in parallel, if one is getting more
than its share, it heats up, *increases* resistance, which redirects more
corrent to the other items.

It looks like mechanical relays are much cheaper, although they are only
rated
up to 40 A (something about UL rating ?).
If I just put 2 relays in parallel to switch that 60 A, will they share the
current properly (like MOSFETs) ?

Is there any tech notes talking about putting relays in parallel ? I didn't
find
any at
  http://siemens.com/
  http://www.azettler.com/
  http://www.pandbrelays.com/
.

I hear that if I put lots of (BJT) npn transistors in parallel, when one
gets
more than its share, it heats up, *decreases* in resistance, then the
positive
feedback (``thermal run-away'') makes that transistor blow up, soon followed
by
its neighbors. That doesn't happen with relays, does it ?

--
David Cary

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