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Old 29th May 2007, 07:07 PM   #1
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Default Toroidal core for Elliott Project 89

Hi I want to build a SMPS based on the one showed here http://sound.westhost.com/project89.htm.

The input will be 12v-14v and the output should be +-25v running at 150 watt continual and 300 watt peak.

The SMPS will feed 4 x lm3886 in a 2 way active system.

And now the questions:

Which core should I use and can you guide me to one that I can buy in denmark, sweden or germany?

What frequency should I be runing the SMPS at?

Should the SMPS be regulated?
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Old 29th May 2007, 08:27 PM   #2
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hi

in europe,you can use 3c80-3c85-3c90 material (philips)

n27 or n67 (siemens )

b2 (i don't know )

with this kind of material you can increase pwm frequency up to 50-60 khz with low losses

but for a good smps efficiency,around 30 khz is a good choice

amount of power vs total losses


you can work with a fixed frequency,but have a good choice for ratio transformer
the secondary voltage will quickly go down when the primary voltage decrease.
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Old 29th May 2007, 08:30 PM   #3
luka is offline luka  Slovenia
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Hi

I am just going to say about freq. and regulation.

Regulation: Yes I think it would be best to have it.

Freq: well as all will say, depends on core, but I just winded my and then starter at 150kHz an went down to as low as I could, without output saging. I have output of +/-47Vdc and found that with my core that I have no info for it, it was best to have freq around 18-22kHz. Many will say that that is a bit too low, but at that point smps was puting out 270w, and would alot more if I would allow saging.
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Old 2nd June 2007, 07:43 AM   #4
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hello

use around 40 khz for a single core (40 mm diameter) with 3c85
you can get mote than 450 w at the output.

20 khz,i think for 300 w is a bit low,temp core will increase,and losse too
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Old 2nd June 2007, 09:38 AM   #5
luka is offline luka  Slovenia
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Hi

Go then for 30k, more then enough
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Old 3rd June 2007, 04:36 PM   #6
djQUAN is offline djQUAN  Philippines
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using a test half bridge oscillator that I made on a ferrite core that I got using single wire test windings, I found that it is most efficient at 27kHz. (1nF and 27kohm for a TL494 chip) and the SMPS that I made with the cores have perfect square waves even without any snubbers.
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Old 6th June 2007, 08:06 PM   #7
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hi

any load on your test bord smps ?

maybe with high current,square waves may show some over voltage .

for safety you should use snubber arround the mosfet, (it's not very expansive and more safetly )
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Old 7th June 2007, 06:43 PM   #8
djQUAN is offline djQUAN  Philippines
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the finished SMPS has space for snubbers but I have not done power testing since my oscilloscope is not working properly so there is little progress.
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