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Old 4th September 2008, 12:33 PM   #31
h_a is offline h_a  Europe
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Thanks for your help!!

A regulator after the SMPS seems a good idea as I regularly hear that SMPS have a lot of noise on the output rails, especially at high frequencies. Sure a regulator would get rid of at least a part of that.

What about pcb-layout?

In general pcb-layout seems critical; however here ICs do the PWM, so my impression is that in this special case the layout is not more critical than for other circuits- true?

Have fun, Hannes
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Old 4th September 2008, 01:35 PM   #32
luka is offline luka  Slovenia
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Hi

Regulators won't regulate noise away, only good output filter of smps will minimize it as much as possible. I had no noise problems...

As for layout goes, apart from all the safetys you should take, it is pretty straightforward, you place element as you want them then start connecting, put them in groups or something, like primary side (caps and fets are near each other, so is trafo and so on), then secondary,.. Or copy someoes design and change something if you wouldn't like

Quote:
In general pcb-layout seems critical; however here ICs do the PWM, so my impression is that in this special case the layout is not more critical than for other circuits- true?
So far I have found layout to be critical only in swithching amps, because of sensitive input circuit and high freq./high current output...if not done right you can have problems...but I didn't have this with any smps
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Old 4th September 2008, 04:02 PM   #33
Eva is offline Eva  Spain
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If a SMPS is leaking RF to the outputs, no linear regulator will solve the problem, it may make it worse if you manage to add more RF resonances (pass transistor capacitances plus layout inductances). The SMPS has to be designed to be quiet.
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Old 4th September 2008, 04:42 PM   #34
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Default Re: PCB for SMPS +/-50V

Quote:
Originally posted by alex mm
Hi folks.

Another PCB variant http://freepdfhosting.com/3bb9b920ad.pdf not tested , but I hope to be good all the best alex mm
Hi Alex mm

Another nice board layout...

Do you mind sharing the PCB files? I am thinking about prototyping your board in the near future. The plan is to use this SMPS to power the DX HR Turbo.

Thanks!
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Old 4th September 2008, 05:28 PM   #35
Eva is offline Eva  Spain
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Be very careful, there is no primary side to secondary side clearance on that PCB layout. At least 5mm are recommended.
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Old 5th September 2008, 05:14 AM   #36
Eva is offline Eva  Spain
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The negative output rail is not connected to the diodes properly either.
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Old 5th September 2008, 07:48 AM   #37
h_a is offline h_a  Europe
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Quote:
The SMPS has to be designed to be quiet.
Hi Eva,

that's exactly the problem. Finding a schematic, ideally with board layout (in my needed size ) of a proven, quiet SMPS. So one of yours would be nice.

I've been looking for quite some time for such a thing, but usually it's not fully tested or it has tons of features I don't need (that I would need to strip from the board-layout) or is overkill power wise. Or uses a non-standard core so that one cannot clone it.

Or do you guys know a proven, quiet 300-400W SMPS for symmetric rails?

I would be interested to drop the usual transformer-psu and use such a thing for my power amp Just for sake of doing something more interesting.

Any links appreciated!

Have fun, Hannes
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Old 5th September 2008, 07:58 AM   #38
h_a is offline h_a  Europe
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By the way, why's that SMPS-board that large? It's larger than a 300W transformer?

Why does it use 2x 470uF/400V caps? These don't exist on the schematic?

I suppose they replace the 4x 600uF/200V caps? I can't see the need for 400V parts here.

Guys, be aware that the layout is not 1:1 identical to the schematic.

Have fun, Hannes
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Old 12th September 2008, 08:05 PM   #39
stcboy is offline stcboy  Saudi Arabia
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Hi Mahmood

Can you send to my email the file for the pcb layout as I cannot email you since I'm still on supervised by the moderator. and also can I use toroid transformer in the output and lastly if I want to convert to 13.6vdc as output what would be the winding in the transformer?

my email: stcboy2002@yahoo.com

thanks
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Old 12th September 2008, 10:12 PM   #40
mahmood is offline mahmood  Iran
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Default request

hello

dear stcboy

please check your mailbox . in the zip file u can find

1: my spms main file that open with pad2pad software
2: an108 that is a smps calculations based on toroidal core

and this is good . from chas1:

calculating the volume for the transformer plus number of turns Post #5
To answer your question, you will find many methods for calculating turns and core size. I will try to explain a easy one for me. You must remeber all methods are based on Faraday's law and just rearranged so you can find the unknowns.

Faraday's law:
E= N*AE *(dt/dt) * E-8

E is the voltage across the transformer winding, N is the number of turns on the winding, Ae is area of core in cm^2, DB is flux change (gauss) and dt time for flux to change (seconds)

Now we rearrange the terms and plug in some definitions and we can get the following for finding number of primary turns.This is for halfbridge. For Forward or Fullbridge you double this number because they have to support the rectified mains not just half.

V(in) * E8 / (4 * Fs * Bmax *Ae) = NT(pri)

Now for the core volume to support the power we need:

Lets set up a design for 500watts:

The primary current will be equal to :
Ip= 3 *P(out) /V(in)

V(in) will be calculated based on 110VAC line at it highest value:
130 VAC therefore with a voltage doubler we can expect about:

2(130 * 1.4) = 370 VDC after rectifiers
therefore Ip = 1500 /370 = about 5 Amps from this we calculate the input power which is 1500/ .85 for 85% eff which is about 1750 watts.

core size = .68 * P(out) * current density / Fs * Bmax

Choose a industry standard of 500 c.m. /A for current density and we get:

AcAe = .68 * 1500 * 500E3 / 100E3(Fs) * 1200 (bmax) =4.25 cm^4

If we check the ETD49 specs we find that its AcAe is about 5.7 cm^4 which is a good choice for this design

Look what happens when we raise the Fs to 200KHz:
AcAe = .68 * 1500 *500e3 / 200e3(Fs) *1200(bmax) =2.125 cm^4

so you can see the higher the frequency the smaller the core within reason (copper loss, core temp and other things come into play)

In this case we used a Bmax of 1200 and could have used up to 1600, recalucate using 1600 and then we get 3. 18 cm^4 which means we might be able to use an ETD44 coreset now for the turns calculation:

If we use the highest voltage we expect on our transformer windings when the supply turnon:

N(pri) = 370(V(inmax)E8 / (4 * 100E3 * 2400(B(max) *2.11(Ae) =
18Turns for ETD49 and for ETD44 = 23 Turns

Now a good guess for the secondary is Ns = VS/VP I want an output of 35 volts , so that means after the rectifiers I need twice that and to help with transits and load changes I will increase that by 5% or so make it 80 volts , I expect at low line to have about 110 volts after the main rectifiers using a 110VAC input so now my secondary turns will be :

18*(80/110) = 13 turns make it 14, After you wind and test your transformer you might find you need to add or take off a winding or two. And at high line you wil need 11 turns make that 12.

So there is your transformer calculations regardless of how you do it the frequency along with the Amount of flux will determine the output power and the core size along with the size of the winding area and wire size.

All this is more or less what I have found in appnotes,books and other articles plus a little experience mixed in. It is up to the designer or DIY to verify this thru research and reading as this forum is full of material covering this subject and I will not get in a contest with which is right or wrong, however if you find an error or have a question I will try to help if I can and I will correct the errors you find ... just remeber a transformer is just that and the law and priciples for their design is basic and well documented its just when you lump them into a design at high frequency that a lot of care must be taken for them to provide proper results.

thank u chas1

chek this page for toroid core data table :

http://coremaster.com/2000_core.htm

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