
Home  Forums  Rules  Articles  The diyAudio Store  Gallery  Blogs  Register  Donations  FAQ  Calendar  Search  Today's Posts  Mark Forums Read  Search 

Please consider donating to help us continue to serve you.
Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving 

Thread Tools  Search this Thread 
26th January 2011, 05:45 PM  #1 
Banned
Join Date: Oct 2010

SMPS Transformer Primary Turns Calculations
Hello I found this formula helpful to any one who build SMPS. It will calculate Turns for SMPS Transformer. Primary And Secondary, look carefully before you enter values, cos it confuse. * however, its as is as I found! Good Luck 
15th February 2011, 08:05 PM  #2 
diyAudio Member
Join Date: Apr 2010


15th February 2011, 08:11 PM  #3 
diyAudio Member
Join Date: Feb 2011

I also wish to design a transformer.
In my case, a toroidal will be used. The input current is sinusoidal and the transformer will step up it 3x higher than primary voltage. Kindly share if you know how to design it. It's designed for 10kHz application. Thanks. 
10th January 2012, 08:01 PM  #4 
Banned
Join Date: Sep 2011

this formula is good for toroidal cores?

11th January 2012, 08:59 AM  #5 
diyAudio Member
Join Date: Apr 2010
Location: seattle, wa

OP's spreadsheet is worse than mine.
http://johansense.com/bulk/spreadshe...merdesign1.xls that said, it will work for toroids, just enter the core sizes that pertain to the proper dimensions. but the only useful math you'll get is the turns count. 
12th January 2012, 04:39 PM  #6 
Banned
Join Date: Sep 2011

oops, your formula lookx complex also

14th January 2012, 07:00 PM  #7 
diyAudio Member

Easy.
N = Vrms / (4.44 * F * B_max * A_e) Easy to remember because 4.44 might be familiar from books on transformers, and if you keep track of the units, you can remember: Vrms in volts F in 1/sec therefore, V / (4.44 * F) == Phi_max, peak flux B_max in tesla == flux/area per turn (uV.s/mm^2.t are handy engineering units) therefore, Phi_max / B_max = mm^2.t Finally, divide by A_e of whatever core you're looking at to find number of turns. Alternately, if you want the area for a given number of turns, divide by turns instead to get A_e. This is handy when you need a large current and can only get a single turn foil winding to handle it. 1/4.44 comes from: 1/4 because the magnetic flux goes from zero at the voltage peak, up to its maximum value at the voltage zero crossing, hence only a quarter of the wave needs to be considered; 4/pi ~= 1.11 comes from the integral of the sine wave (this also shows up in chokeinput rectifiers, because the average value of a fullwave rectified sine is pi/4 times the input peak); and sqrt(2) comes from the RMS to peak conversion for the sine wave. For square waves, the factor is NOT 4.44, but 4.0 even, and the voltage is simply the applied squarewave voltage (Vrms = Vpk for a true square wave, so it doesn't matter). This applies most directly for forward converters at maximum duty cycle. This also applies to half wave converters (forward/flyback) in CCM, with double the turns, because the flux only goes one way. For more detail and complete transformer formulas, try this: Magnetics For any given core geometry, you can develop a rough formula relating a proportional dimension (like overall size) to an overall property (like core product, mm^4) to calculate, in one step, what minimum size core is required for a particular voltage and current capacity. Inductors can be calculated in the same way, with the additional feature of gap length, which is calculated from desired inductance (in transformer design, the core's permeability is assumed high enough that the resulting inductance is not a concern for the user, i.e. load current is higher than magnetizing current). Tim
__________________
Seven Transistor Labs, LLC Projects and Resources / Electronic Design and Consultation 
Thread Tools  Search this Thread 


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
transformer primary winding turns  AndrewT  Power Supplies  19  20th December 2010 01:11 AM 
SMPS calculations  mahmood  Power Supplies  4  8th December 2009 10:17 AM 
Calculating Bmax and primary turns etc...  guitar_joe  Power Supplies  4  5th July 2007 09:06 AM 
shorted turns in primary?  mrshow4u  Solid State  15  12th September 2006 05:09 PM 
SMPS Transformer Turns Equations Help  venki  Power Supplies  4  16th February 2006 01:02 AM 
New To Site?  Need Help? 