Vertical Mounted PCB on Switching Converters

[D from BC]

And now for something technical...

I've noticed smps's sometimes have a small vertical mounted
PCB.. Most likely it's the controller..but not every smps is
like this..
(For reference, see pictures of open chassis smps's on ebay.)

My initial guesses are:
1) Better grounding scheme
2) Orientation to dodge electric and magnetic fields from power
components
3) Enables the controller PCB to be changed either before or
after production
4) Enables single sided PCB
5) Enables shortest connection to power MOS or other
6) Orientation to dodge hot components

Is a vertical mounted controller PCB the best way in a smps?
And what is the main reason it's designed like that?

D

 

[David L. Jones]

And now for something technical...

I've noticed smps's sometimes have a small vertical mounted
PCB.. Most likely it's the controller..but not every smps is
like this..
(For reference, see pictures of open chassis smps's on ebay.)

My initial guesses are:
1) Better grounding scheme

For single sides boards - yeah, it can help a lot.

2) Orientation to dodge electric and magnetic fields from power
components

Don't think so.

3) Enables the controller PCB to be changed either before or
after production

Maybe, that's kinda handy.

4) Enables single sided PCB

Yep, can be a big benefit.

5) Enables shortest connection to power MOS or other

It doesn't hurt.

6) Orientation to dodge hot components

Don't think so.

Is a vertical mounted controller PCB the best way in a smps?

As always, it depends.

And what is the main reason it's designed like that?

If you are short on board area for some reason, it's a good choice.
If you want future flexibility to change the controller type/package
etc it's handy.
Might be cheaper if your main PCB is single sided and your controller
is some SMD package or something, saves double side loading. Get the
main single sided board made cheaply, then the controller can be double
sided or whatever and manufactured elsewhere, then simply inserted like
a component.

Dave

 

[Emanuele]

D from BC ha scritto:

And now for something technical...

I've noticed smps's sometimes have a small vertical mounted
PCB.. Most likely it's the controller..but not every smps is
like this..
(For reference, see pictures of open chassis smps's on ebay.)

My initial guesses are:
1) Better grounding scheme
2) Orientation to dodge electric and magnetic fields from power
components
3) Enables the controller PCB to be changed either before or
after production
4) Enables single sided PCB
5) Enables shortest connection to power MOS or other
6) Orientation to dodge hot components

Is a vertical mounted controller PCB the best way in a smps?
And what is the main reason it's designed like that?

D

Another features is that You can make a 70micron solder (or much more)
in a only Power board, with the vertical control board in smd.
All points You write is good, only for the 2 i don't know but i see
al lot of circuit with vertical board controller

Infineon 200W smps reference project for example

Emanuele


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[[email protected]]

I've noticed smps's sometimes have a small vertical mounted
PCB.. Most likely it's the controller..

Some parts of a power supply handle high currents, and the copper
on the printed wiring board is thick to handle the current. It's
cheaper to etch thin copper, and quicker to heat it to solder
temperature.

So, a small board with surface mount components on both sides can
be IR-reflow-oven soldered, while the large board, components
crimped in place on one side only, with thick copper, is wave-soldered.

 

[Terry Given]

And now for something technical...

I've noticed smps's sometimes have a small vertical mounted
PCB.. Most likely it's the controller..but not every smps is
like this..
(For reference, see pictures of open chassis smps's on ebay.)

My initial guesses are:
1) Better grounding scheme

possibly, but probably not. many smps have terrible layouts.

2) Orientation to dodge electric and magnetic fields from power
components

again, possibly but probably not. If the layout is bad, then they
clearly werent considering E & H fields.

3) Enables the controller PCB to be changed either before or
after production

No. why would you want to do this? The object of the exercise is to
build things that work first time....

what it can give you is a standard SMT controller that can be used in
various products, and the controller can also be tested before being
soldered into the main smps, which can simplify the final tester.

4) Enables single sided PCB

likely. cheaper is better....

5) Enables shortest connection to power MOS or other

it can do.

6) Orientation to dodge hot components

possibly. usually heat isnt the problem for controllers, it is for the
electrolytics, which usually sit right beside the heatsinks!

what it does do is make life much easier wrt voltage creepage and
clearance. So if you mean electrically "hot" then Yes!

Is a vertical mounted controller PCB the best way in a smps?
And what is the main reason it's designed like that?

D

All the other posts make good points, and:

- often its far cheaper to do discrete SMT than use dedicated controller
chips (eg UCC38xx), but this requires more space. My last smps used a
Fairchild controller that cost US$1.50 in volume; the one I am now doing
(using this vertical PCB approach) costs NZ$0.25 1-off, and every part
is multiple-sourced, but it needs about 4x the PCB area.

- there is often a lot of wasted space inside a smps, and going 3-D
helps fill it up - minimising waste space gives a smaller package

- heavy current PCBs have minimum track widths and separations that can
be incompatible with fine lead pitch SMT. the last 4-Oz PCB I did
(1-4-4-1 Oz 4-layer) had a min track width of 15mil, and a min spacing
of 18mil per vendors instructions, but we still had problems with shorts
(5% failure rate), so I upped the separation to 22mil, and 20k units
later that seems to have worked pretty well (5 PCB failures). Some of
the fine lead pitch devices I use have a 7.92mil gap between pads (so
much for 8/8 design rules), and I dont use the really small stuff!

bear in mind most smps are designed for minimum cost.

Cheers
Terry