The problem is Andrew some of these board use close to that amperage.
For those that are run near that limit (e.g. the V2 SMB, it takes 1.38 Amps) they get real hot unless you have a very large heat sink (like Cromemco) but there goes about 20% of the boards surface area. I don’t really know how these TO-2 regulators work, but they seem to generate much less heat – or at least radiate it better, probably the latter.
Those HEX displays are real power hungry! Interestingly enough (and much to my surprise), my new 80386 board only consumes a total of0 .78 amps total. 78H05’s sure are way overkill!
John
From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of Andrew Bingham
Sent: Wednesday, June 4, 2014 4:24 PM
To: n8vem...@googlegroups.com
Subject: Re: [N8VEM-S100:3958] Re: Power distribution across an S100 Board and voltage issues with TO-3 Regulators..
If only 1.5A is needed, a TO-220 3-pin design would allow use of http://www.murata-ps.com/data/power/oki-78sr.pdf
Andrew B
On Wednesday, June 4, 2014 3:03:38 PM UTC-7, Rob Doyle wrote:
On 6/4/2014 8:54 AM, John Monahan wrote:
> I agree with Tom, In general I never (fall for) cheap Chinese chips on
> eBay. But I have to say, UTSource seems to be an exception. I’ve gotten
> probably about 6 packages from them over the years. Not yet,
> V-regulators, but in every case the chips were 100% fine, and on the
> surface definitely appeared to be the genuine article. Some (video
> chips)were in their factory packages.
>
> It seem like there is a flood of 323k knockoff’s out there. I have
> actually been using 78H05’s These are 5V, 5A regulators. Yes I know
> overkill for our boards. But I happen to have an old stock of them
> here. Perhaps we should search around for these.
>
> I like Ian’s idea of checking out used parts stores. I have not done
> that in a while. I think I going to drop by a local one here ,
> http://www.weirdstuff.com/ for anybody that lives in the bay Area.
>
> John
I think a far better answer would be to start including a switching
power supply option (in addition to the LM323K) when designing new
boards. A builder could stuff the board either way. Something like:
http://www.digikey.com/product-detail/en/LM2576T-5.0%2FNOPB/LM2576T-5.0%2FNOPB-ND/212636
http://www.ti.com/lit/ds/symlink/lm2576hv.pdf
At $2.83, it saves money and heat.
We could probably design a little tiny circuit board that could adapt
the LM323K footprint to this switching power supply design for retrofit
uses.
Rob.
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