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 27th August 2012, 01:43 PM #1 ISTPYRO   diyAudio Member   Join Date: Aug 2012 Help with SMPS Transformer Hello guys, I am new around here and I need some help to build my SMPS transformer. I was thinking designing a transformer to use on a forward converter. My goal is to, first, learn how to do a transformer and second, how the forward converter works. I was wondering if there is someone who can help me out here with the design of that trafo. I will wait for some answers and see if someone can help me. After that, I'll post the specifications and the calculations that I have done so far. Kind Regards.
 27th August 2012, 08:07 PM #2 ISTPYRO   diyAudio Member   Join Date: Aug 2012 Hi again. Maybe would be better to post directly the specifications. Specifications Input Vin = 230VAC Vin(nominal) = sqrt(2) * 230VAC = 325V Vin(minimum) = 300V Vin(maximum) = 350V Output Vout = 30V ; Iout = 5A ; Pout = 150W Expected efficiency = 80% Pin = 150W / 0,8 = 190W Iin(maximum) = 190W / 300V = 0,65A Transformer specifications: I got this transformer from an old power supply. It is an EI type core. I don't know what kind of core material and because of that I do not intend to strive the transformer that much. The specifications are: Bmax = 1600Gauss Ae (center leg cross-section) = 1,21cm2 f = 100kHz TRANFORMER CALCULATIONS Just before start, I have a couple of questions here. From what I have read, in forums, books, applications notes, there are two methods to calculate the primary transformers turns. The first one is: Np = ( Vin(min) * Delta(max) ) / (Ae * Bmax * f ) Ns = Np * ( (Vout + Vf * Delta(max) ) / ( Vin(min) * Delta(max) ) ) The second one is: Np = ( Vin(max) * 10^8 ) / ( k * f * Ae * Bmax ) Ns = Np * ( ( Vout + Vf ) / Vin(min) ) The Ns, from the first method I saw it on a paper, but I have seen too the Ns from the second method, applied on the first. I have calculated the turns with both methods and both turns gave me completely different values. Here they are: Using the first method I got: Np = 70T ; Ns = 17T; Using the second method I got: Np = 45T ; Ns = 5T; Now my question is, which method should be used? Why they give so different values? The method that doesn't use the Delta, is less accurate than the other? I would appreciate if someone could help me out. Kind regards.
dtproff
diyAudio Member

Join Date: Oct 2008
Location: Plano, TX, USA
Quote:
 Originally Posted by ISTPYRO Hi again. Maybe would be better to post directly the specifications. Specifications Input Vin = 230VAC Vin(nominal) = sqrt(2) * 230VAC = 325V Vin(minimum) = 300V Vin(maximum) = 350V Output Vout = 30V ; Iout = 5A ; Pout = 150W Expected efficiency = 80% Pin = 150W / 0,8 = 190W Iin(maximum) = 190W / 300V = 0,65A Transformer specifications: I got this transformer from an old power supply. It is an EI type core. I don't know what kind of core material and because of that I do not intend to strive the transformer that much. The specifications are: Bmax = 1600Gauss Ae (center leg cross-section) = 1,21cm2 f = 100kHz TRANFORMER CALCULATIONS Just before start, I have a couple of questions here. From what I have read, in forums, books, applications notes, there are two methods to calculate the primary transformers turns. The first one is: Np = ( Vin(min) * Delta(max) ) / (Ae * Bmax * f ) Ns = Np * ( (Vout + Vf * Delta(max) ) / ( Vin(min) * Delta(max) ) ) The second one is: Np = ( Vin(max) * 10^8 ) / ( k * f * Ae * Bmax ) Ns = Np * ( ( Vout + Vf ) / Vin(min) ) The Ns, from the first method I saw it on a paper, but I have seen too the Ns from the second method, applied on the first. I have calculated the turns with both methods and both turns gave me completely different values. Here they are: Using the first method I got: Np = 70T ; Ns = 17T; Using the second method I got: Np = 45T ; Ns = 5T; Now my question is, which method should be used? Why they give so different values? The method that doesn't use the Delta, is less accurate than the other? I would appreciate if someone could help me out. Kind regards.
As to your question above, please check out this app note... http://www.fairchildsemi.com/an/AN/AN-4134.pdf

It will go a long ways in explaining things. After you have read through it we can chat some about the important design considerations around a forward converter.

Tony

 29th August 2012, 10:18 AM #4 ISTPYRO   diyAudio Member   Join Date: Aug 2012 Thank you Tony. I'll read that. Regards.
dtproff
diyAudio Member

Join Date: Oct 2008
Location: Plano, TX, USA
Here is a fairly thorough treatment of a forward converter that I wrote about 10 years ago but it still applies today.

Tony
Attached Files
 150W 3A 48V Forward PQ2625-PC40.pdf (66.4 KB, 151 views)

 10th April 2016, 12:27 AM #6 Bzzas diyAudio Member   Join Date: Apr 2016 Hi Tony Would you share the schematic of this Forward converter? Thanks Jack
 10th April 2016, 06:50 PM #7 powerbob diyAudio Member   Join Date: Aug 2010 dtproff, in the past you had posted a design procedure for flybacks but i was unable to find it. Could you please post it again.
dtproff
diyAudio Member

Join Date: Oct 2008
Location: Plano, TX, USA
Quote:
 Originally Posted by powerbob dtproff, in the past you had posted a design procedure for flybacks but i was unable to find it. Could you please post it again.
Attached is the pdf of the math used for a Quasi Resonant flyback.

Tony
Attached Files
 TM Flyback controller Math.pdf (511.5 KB, 33 views)

dtproff
diyAudio Member

Join Date: Oct 2008
Location: Plano, TX, USA
Quote:
 Originally Posted by Bzzas Hi Tony Would you share the schematic of this Forward converter? Thanks Jack
Sorry, I don't have it any more.

AndrewT
diyAudio Member

Join Date: Jul 2004
Location: Scottish Borders
Quote:
 Originally Posted by dtproff As to your question above, please check out this app note... http://www.fairchildsemi.com/an/AN/AN-4134.pdf It will go a long ways in explaining things. After you have read through it we can chat some about the important design considerations around a forward converter. Tony
searching Fairchild for an4134 took me here:
https://www.fairchildsemi.com/techni...wer-Supply.pdf
__________________
regards Andrew T.

Last edited by AndrewT; 9th October 2016 at 09:40 AM.

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