Re: Bulletproof your WG6100!

>>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.

I feel lucky.

>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..."

Yea. That'd be cool. he he.

>>At any rate, shorting the pass (power) transistors will not harm the new
>>regulator board.
>
>That's true!

This *is* the best feature of the new LV PCB.

>>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.

True. One thing that I had thought would help protect both the power pass
transistors, and the deflection transistors, would be to add a TVS
(transient voltage suppressor) accross the collector-emitter. This would
clamp any voltage spikes. It is just a matter of soldering one directly
across the ce of the transistor!

>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.

Like you said, may not be worth it.

-Anders.

 -----------------------------------------
| Anders Knudsen
| ASIC Design Engineer
| Adaptec, Inc., Boulder Technology Center
| anders_knudsen@btc.adaptec.com
| http://www.adaptec.com
 =========================================
Received on Wed Jan 14 14:54:20 1998