# Max power density of SMPS?

Discussion in 'General Electronics Discussion' started by eem2am, Feb 22, 2014.

1. ### eem2am

414
0
Aug 3, 2009
Hello,
We need to design the following Buck-boost converter for 650W.
Vin = 18 to 32V
Vout = 5 to 34V
Output power = 650W

Do you know of any PWM controllers on the market which can implement this?
I believe that a synchronous boost controller could do the job?
I believe that we will need to implement isolated high side bias supplies to power the upper fet gate drivers.

Also, do you believe that the current sense transformer primary should be placed upstream of the most "upstream" fet (ie upstream of M4 or M8)?
(Schmatic and LTspice simulation of the basic 4 fet buckboost converter attached)

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2. ### eem2am

414
0
Aug 3, 2009
Hello,
What is the accepted limit of power density (in W/cubic inch) for a SELV (all voltages inside <42V) SMPS without a fan, but has potting around all the electronics, and has a metal heatsink.?
Is it about 100W/cubic inch?
Ambient temperature 85 degrees C max
(My 230VAC laptop power supply is 65W in 7 cubic inches. (10W/cubic inch))

3. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,401
2,777
Jan 21, 2010
Wait! I thought you were the expert?

4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,401
2,777
Jan 21, 2010
Wait!

I thought you were the expert?

5. ### eem2am

414
0
Aug 3, 2009
Well...maybe not...I have been asked to do a 680W output SMPS, for 18-32Vin and 5 to 34Vout...at 200KHz, nonisolated smps, and all voltages SELV (<42V).
Its for supplying a fuel pump.
The space we have been given implys 120W/cubic inch, which to me , seems too small, what do you think, may I ask?

6. ### eem2am

414
0
Aug 3, 2009
no, this is quite a rare form of buckboost, there don't seem to be controllers...it looks like a roll your own job, with high side bias supplies etc etc.

7. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,401
2,777
Jan 21, 2010
It depends on what's inside and what's outside the cubic inches you have, oh and what counts as "inside".

But yeah, on the face of it, I would wonder if I could fit the inductors in that space. I would next wonder about cooling.

But as I said, you're the expert. I'm expecting you to tell us how it should be done.

And this is my last post on this thread. I've spent far too much time on your question lectures.

edit: Except to say I'm giving you another holiday to let you consider keeping a single question in a single thread in the future.

Last edited: Feb 23, 2014
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