Re: Bulletproof your WG6100!

On Wed, 14 Jan 1998 15:03:12 -0700, Anders Knudsen
<Anders_Knudsen@btc.adaptec.com> wrote:

>>Don't think I'm not interested (I am) but the last design you had was not
>short
>>circuit proof, have you tried connecting a jumper across the output to see
>what
>>happens to those pass transistors?
>
>I have been meaning to to that! I'll give it a jolt tonight and report what
>happens.

It's probably not worth doing, there's nothing protecting the transistor it that
case. So one of two things will happen:

1) It will survive (possibly stressing your pass transistors for a future
failure). This'll prove nothing (except your a lucky guy!) because there's
still nothing protecting the pass transistors.

2) It will destroy your pass transistors which you will have to replace, at
which point you have to ask, "Why the hell did you put a wire across the output
when you know it was going to destroy the transistor? Are you going to pour
sugar in your gas tank next to see if it really gums up your cars engine? Maybe
it will, maybe it won't..."

>At any rate, shorting the pass (power) transistors will not harm the new
>regulator board.

That's true!
>
>>Either way I'm not sure short circuit proof is that big a deal and I'm
>>interested in a few of these even if they're not short proof.
>
>I did not add any short circuit protection to the LV PCB because it is not
>necessary. If the pass transistors do short, the LV PCB will not be damaged
>(not so with the old original design!)
>However, adding some kind of short circuit protection to the pass (power)
>transistors themselves would be a good idea. I have some short circuit
>protection schemes jotted down on paper, specifically a foldback current
>limit circuit, that could easily be added to the power transistors. I'll
>add it to my list of things to do when I am done with the fab order.

I think it's more trouble than it's worth. The best I can tell voltage surges
seem to be the culprits that kill the X/Y transistors, not too much current. I
believe current wise the transistors are highly overrated, yet they still die.

However you do it, adding current protection to the schematic is easy, but it
means a bit more hacking on the WG monitor. You'll lose your nice and easy drop
in replacement.

It wouldn't be hard to explain to someone how to add current limiting and let
them do it if they want. I've never seen it done (for the low voltage supply)
on any X/Y monitor I've seen the schematic to.

-Zonn

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Received on Wed Jan 14 14:33:46 1998