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From: John Larkin on 18 Jul 2010 16:52
We blew up a couple more of the SIP dc/dc converters, CUI type VASD1.
This one is 12 volts in, +-15 out, rated 1 watt. I don't totally blame
the bricks, since certain un-named parties likely shorted the outputs
while probing channels, but it would be nice if they could stand a
load short.

There are 12 on this board...

ftp://jjlarkin.lmi.net/V220_top.jpg


Anyway, I took one home and tore off the potting shell. It's potted
with something soft and a bit gritty, maybe a filled soft epoxy.
Looking around the garage, I had some Jasco paint remover (methylene
chloride mostly) some acetone, and some MEK, so I mixed them all in a
glass jar and soaked the thing overnight. The potting swelled up and
got really soft. I did lose the transformer, which stayed in the epoxy
glob when I ripped it off the board.

ftp://jjlarkin.lmi.net/VASD1_top.JPG

This looks like a simple 2-transistor forward converter on the left,
and a couple of dual diodes and caps on the right. The substrate is a
pc board, unlike the Muratas which are ceramic.

Maybe we'll add a polyfuse or something to protect them, although
things like this tend to quit failing when people quit probing.

With another part or two, they could have made this short-resistant.
But these are only about $4 each and work very nicely otherwise.

John


From: Joel Koltner on 18 Jul 2010 17:21
John Larkin wrote:
> ftp://jjlarkin.lmi.net/VASD1_top.JPG

I'm surprised someone decided to get "fancy" and mount a capacitor at a 45
degree angle...

On your board they look rather thick -- I take it the transformer is what
makes them so thick? (Since the PCB you show there sure isn't...)

---Joel

From: Tim Williams on 18 Jul 2010 17:29
Yuck, hard switching into a capacitor, too? I'd rather use one of these. Regulated, current protected, and only twice as many transistors.
http://webpages.charter.net/dawill/tmoranwms/Circuits_2010/Fast_DCDC.png

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message news:7ap646lto6hs7j6u8iu5ueh1i89960dntb(a)4ax.com...
> We blew up a couple more of the SIP dc/dc converters, CUI type VASD1.
> This one is 12 volts in, +-15 out, rated 1 watt. I don't totally blame
> the bricks, since certain un-named parties likely shorted the outputs
> while probing channels, but it would be nice if they could stand a
> load short.
>
> There are 12 on this board...
>
> ftp://jjlarkin.lmi.net/V220_top.jpg
>
>
> Anyway, I took one home and tore off the potting shell. It's potted
> with something soft and a bit gritty, maybe a filled soft epoxy.
> Looking around the garage, I had some Jasco paint remover (methylene
> chloride mostly) some acetone, and some MEK, so I mixed them all in a
> glass jar and soaked the thing overnight. The potting swelled up and
> got really soft. I did lose the transformer, which stayed in the epoxy
> glob when I ripped it off the board.
>
> ftp://jjlarkin.lmi.net/VASD1_top.JPG
>
> This looks like a simple 2-transistor forward converter on the left,
> and a couple of dual diodes and caps on the right. The substrate is a
> pc board, unlike the Muratas which are ceramic.
>
> Maybe we'll add a polyfuse or something to protect them, although
> things like this tend to quit failing when people quit probing.
>
> With another part or two, they could have made this short-resistant.
> But these are only about $4 each and work very nicely otherwise.
>
> John
>
>
From: John Larkin on 18 Jul 2010 19:17
On Sun, 18 Jul 2010 16:29:21 -0500, "Tim Williams"
<tmoranwms(a)charter.net> wrote:

>Yuck, hard switching into a capacitor, too? I'd rather use one of these. Regulated, current protected, and only twice as many transistors.
>http://webpages.charter.net/dawill/tmoranwms/Circuits_2010/Fast_DCDC.png
>
>Tim

Lots-o-parts.

The CUI is probably...

ftp://jjlarkin.lmi.net/VASD1_sch.JPG

which is the classic circuit. The resistor has to be small enough to
furnish the worst-base operating base current requirement, which fries
transistors if you short the output. A couple more parts would fix
that, with a smaller startup current and then let the oscillation feed
the bases as it grows.

The FR4 substrate doesn't cool the transistors like ceramic would.

They actually work pretty well. Regulation is good (for certain
definitions of "regulation") and the 1-watt units work fine, barely
warm, at 2 watts. Noise isn't bad at all. It's not worth making your
own for $4, and the sip package uses board height and saves footprint.
They also protect those tiny JTAG headers.

This business is, increasingly, about putting boxes together.

John


From: Robert Baer on 19 Jul 2010 03:47
John Larkin wrote:
> We blew up a couple more of the SIP dc/dc converters, CUI type VASD1.
> This one is 12 volts in, +-15 out, rated 1 watt. I don't totally blame
> the bricks, since certain un-named parties likely shorted the outputs
> while probing channels, but it would be nice if they could stand a
> load short.
>
> There are 12 on this board...
>
> ftp://jjlarkin.lmi.net/V220_top.jpg
>
>
> Anyway, I took one home and tore off the potting shell. It's potted
> with something soft and a bit gritty, maybe a filled soft epoxy.
> Looking around the garage, I had some Jasco paint remover (methylene
> chloride mostly) some acetone, and some MEK, so I mixed them all in a
> glass jar and soaked the thing overnight. The potting swelled up and
> got really soft. I did lose the transformer, which stayed in the epoxy
> glob when I ripped it off the board.
>
> ftp://jjlarkin.lmi.net/VASD1_top.JPG
>
> This looks like a simple 2-transistor forward converter on the left,
> and a couple of dual diodes and caps on the right. The substrate is a
> pc board, unlike the Muratas which are ceramic.
>
> Maybe we'll add a polyfuse or something to protect them, although
> things like this tend to quit failing when people quit probing.
>
> With another part or two, they could have made this short-resistant.
> But these are only about $4 each and work very nicely otherwise.
>
> John
>
>
It has been said, for a car, that addition of a 50 cent part
increases the consumer price by 5 dollars.
So...the addition "of another part or two" would almost double the price.
"QED"

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