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a 3amp 5volt switching power supply

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slburris:
I picked up a 5V 3A power supply board from Sure Electronics.  It's based
on the LM2596 Simple Switcher from National Semiconductor.  The cost
at Sure was about same same as if I just bought the LM2596 alone here in
the US, sadly.  So, for about the same cost, I get all the parts for the power
supply, plus a PIC16F57, crystal, and a header for connecting to the PIC:

http://www.sureelectronics.net/goods.php?id=1139

So let's see what I actually got, board photos attached.  OK, first thing
which strikes me are the diodes at the top and bottom of the inductor,
3 each.  Looking at the schematic, it appears the design parallels 3 1amp
diodes to reach a 3 amp specification.  Really?  What, does a 3 amp diode
cost more than a penny or two more?  Does this even work?  Here's the
schematic and manual:

http://www.sureelectronics.net/pdfs/PS-SP12118_Ver1.0_EN.pdf

I'd expect paralleling diodes to be a bad thing.  Invariably, they will
have different forward voltage drops, and the one with the smallest drop
will take the most current.  Off to the 1N5817 datasheet I got.  Hmm,
so as current increases, the forward voltage increases.  I *think* that
means we'll be OK as far as runaway goes, because the diode with the lowest
drop will carry more current, the Vf will increase, then another diode will
become the lowest.

Still, I would have just used the right diode....

Soldering looks mostly OK, except you can see a solder blob on pin 4 of
the regulator chip.  And what are those jumper wires?  Well, they aren't
exactly jumper wires.  They actually seem to be embedded in the board.
Looking at the back of the PCB, we see even more of these "wires".

Never seen this before -- is this an attempt to draw heat away from the
regulator?   Don't know.  It may not be apparent from the photos, but
the cloudy area around the wires in the back is where the solder mask
had been scraped off the PCB.

So I've got another China product with some, uh, unusual design characteristics.
Next up, I'll have to power this up and do some measurements.

Scott

Kiriakos-GR:

--- Quote ---So I've got another China product with some, uh, unusual design characteristics.
--- End quote ---

Do not start acting like Simon does , or else I will shoot my self ..  ;D



Move forward on testing , this is an more interesting part.


.

Jon Chandler:
I have purchased a number of items from Sure and found them to b e well made, functional and some of them truly innovative designs.  I'm a satisfied customer.


Jon

slburris:

--- Quote from: Jon Chandler on September 17, 2010, 09:03:01 pm ---I have purchased a number of items from Sure and found them to b e well made, functional and some of them truly innovative designs.  I'm a satisfied customer.


Jon



--- End quote ---

I've purchased mostly dot matrix displays and controllers from them in the past.  This board is one of several things I recently bought
and I'll put up some kind of review for all of the items I got in a recent purchase.

Scott

mikeselectricstuff:
Nothing wrong with parallelling diodes of the same type - Although Vf may differ slightly at low loads, the increase in Vf with current will tend balance them. The only thing to watch is that they are reasonably well thermally coupled, as if one can get significantly hotter it may tend to hog current.
The only reason I can think they did this is inventory - e.g. they already had the 1A parts in stock, or use them on other products.

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