nuckolls.bob(at)aeroelect
Guest
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 Posted: Thu Sep 17, 2009 10:46 am Post subject: mc3423 Overvoltage Crowbar Sensing Circuit |
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At 12:11 PM 9/17/2009, you wrote:
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I don't know why my original message didn't get through but what I wrote was:
Pending availability of AEC9004 has anyone looked at implementing the
crowbar in the interim circuit with a mc3423?
One chip, three resistors and an SCR, total cost approximately $4. Any
catches I'm missing?
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The AEC9004 is not an SCR based crow-bar protection
module. The AEC9003 (AEC), OVM-14 (B&C), and CbOVM-14
(AEC) modules are still in production in one form
or another . . .
The 3423 is a well thought out device that would
nicely emulate the functionality of the AEC/B&C crowbar
OV protection modules.
It features a constant current source charging
a clamped dV/dT capacitor to set a "window" of tolerance
for short duration transients. I did an implementation
of the same configuration with dual comparators
a few years after we offered the first OV crowbar
design to Beech. The MC3423 came along some years
later to offer a one-chip implementation of the
idea. As long as our supply of trigger-diodes
holds out, the design we offer will continue with
the minimum-parts-count approach.
It's a slick chip. However, I note that Digikey
has no stock on the DIP8 package it and appears to
offer the SOIC 8 package with only 11 pieces in
stock at .93/ea each right now. Allied has DIP8
chips on hand at .71/ea.
Other folks may have DIP8 packages on hand. If this
chip is going the way that many others do, the
alternatives will be to revisit the dual-comparator
approach I cited earlier. I can supply a schematic
for the design if anyone wants it.
Bob . . .
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( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
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