SMPS Layout

[pokka]

Hi,
I built a SMPS on copper board, and it seems to be working. I drawed over 100 watts out of it without any real heat in the FETs. I'm gonna draw more out of it once it is layed out on a PC board. I've got a push-pull topology with +-35V rails, which will hopefully drive a car amplifier later.
I am going to build the SMPS on it's own i.e. on it's own PC board, with a high current plug connector on the side. My amplifier will plug into this SMPS unit. The reason I'm doing it, is because I actually want to build a Class AB amplifier for my front stage and a Class D mono block for my Subwoofer. The SMPS will be the same, but it won't be able to drive both amps due to power limitation in the output transformer (~500W) I'm using, so I have to build two SMPS for my front stage and Sub amplifiers. It also makes the design process and PC board layout alot easier by having plug in modules.
I'm currently busy with the PC Board layout of the SMPS. This is where I want to spend alot of time on, as layout is very important. I'm going to have a ground plane on the bottom of the board and I want to keep all tracks as "symmetrical" as possible on both FETs side.
I would like to know if it is wise to put circuitry (PWM driver circuits and optocouple feedback) underneath the high frequency transformer. I'm using an ETD49 core, with bobbin and clips. So there's quite a bit of room underneath the transformer. With this design I can make my layout perfectly symmetrical to both side FETs (which is 4 in parallel) . I've got a gutt feeling that it's not good, because of the magnetic field, which might induce noise in the circuitry. Can any of u advise me. I'm using surface mount components.
Thanks

[Alme]

I saw one car amplifier design with SMD components on bottom PCB side, but they were not quite UNDER transformer, rather aside. And transformer was toroid type, so with less external EM field. I don't see a point why you have to economy PCB space in that way. I think practical efficiency of ETD cores is lower than toroids at lower input voltages and high currents like car battery supply, unless you make special primary 'winding' like punched copper plates. Typical is 90% efficiency under steady maximum power load. Half-windings symmetry is some critical only in regard to ohmic resistance of push and pull current path halves if switching freqency is low like 25-35kHz. Don't be scared to make layout looking asymmetrical as this is usual case in real life

[bellx]

Mr Pokka

I am using an ETD49 ,doing over 1kW, in an offline smps, ok it gets a bit warm but it works fine. I don't see a problem for 500w. I kind of like them very much. Have u tried Powerhouse in JHB, they are quite cheap.

bell

[pokka]

Thank you for your replies guys!
I must admit that I don't really like laying out PC Boards. It takes up too much time!! Maybe I'm too impatient, that's why I wanted to place components under my transformer. I'm using Orcad Layout at the moment, which is quite good. I think I'm finally getting somewhere.
Thanks

[Danko]

Originally posted by bellx
Mr Pokka

I am using an ETD49 ,doing over 1kW, in an offline smps, ok it gets a bit warm but it works fine. I don't see a problem for 500w. I kind of like them very much. Have u tried Powerhouse in JHB, they are quite cheap.;)

bell

Hi!

How warm does the ETD49 core heat up?
I'm asking this, becouse i'm building a SMPS, which will do about 500-700watts, and i'm interested in this transformer-waring-thingie :-)

Could you post a picture of you SMPS? :-)

[bellx]

Danko, the smps I built with the EDT is not for a car amp, but rather for 220vac to 13.8v dc , tested up to 80amps.

[bellx]

I will post some pics later of a car amplifier I built that puts out in excess of 1kw, class AB.But it uses toroids not ETD cores.

[Danko]

bellx: i'm making my SMPS also for 230V AC
Here are some pictures of the "stuff":
http://sziget.mine.nu/~danko/aramkor.../9/2004-11-06/
Theese pictures are a little bit old, I had re-designed some parts of the board.
maybe, i will totally redesign the layout of mayor components on the board. ETD orientation, MOSFETs and ouput diodes to be placed on the edge of the board, etcetc

http://sziget.mine.nu/~danko/aramkor.../9/2004-08-19/ this is the very first board :)

What are thoose TO220 packaged devices, bellx? Fast recovery diodes? Why are they necessary to be placed there? I don't use them.

How did you makage the feedback? operational amplifier + optocouple? Or Zener-diode(ot TL431) + optocoupler, or something else?

[microsim444]

I am unable to understand how most users test there SMPS, and determine the POWER, as the above example, have you tested your supply for full load for couple of hours? contnius full load?


It will blow UP

[luka]

Originally Posted by bellx

Danko, the smps I built with the EDT is not for a car amp, but rather for 220vac to 13.8v dc , tested up to 80amps.

80A?? are you sure? really?