How to build own transformer?

[CandleCookie]

Can anyone teach me how to wind the transformer myself. I need a mid-point transformer. For example, this is the core for the transformer.
Ferrite,core,ungapped,EFD25/13/9,2000nH(AL),N87,B66421-G-X187

 

[chuckey]

Do you mean a transformer with a centre tapped primary? What do you want as a secondary? What frequency do you want to use it at and at what power level?
Frank

 

[CandleCookie]

I want centre tapped secondary. The primary is 240V and each of the secondary is 17V. The input frequency is 50Hz and my mosfets are switching at frequency 20k Hz. So I need to get a SMPS transformer. The problem is I don't know how to choose and I don't know how to wind the transformer to become centre tapped.

 

[chuckey]

If you are going the standard SMPS route, the mains goes via a small resistor to a bridge rectifier and a smoothing capacitor, so the DC V available is 240 x 1.4 = ~ 350v, If your mains is 110V then its 160V DC. To make a centre tapped transformer, take twice the length of wire you need, fold it in half, wind the coil with this double wire. Snip the fold, label one wire "A" the other "B". find the other end of wire "A", twist this around wire labeled "B", this is your centre tap.
Frank

 

[RCinFLA]

Sounds like you want a flyback transformer not a push-pull primary. That ungapped core is not suitable for a flyback arrangement.

This link has good overall info on designing both types of SMPS.

**broken link removed**

 

[CandleCookie]

Thanks chuckey. How much is the size of the wire for the transformer?? Do you have any idea where to get a readily made smps transformer?

---------- Post added at 07:00 ---------- Previous post was at 06:53 ----------

Thanks RCinFla. But I need a mid point transformer not a flyback transformer. What is the difference between ungapped and gapped core?

 

[Tahmid]

Hi,
Here you can find a few guidelines on winding transformer with centre-tap: **broken link removed**

I think you should wind your own transformer according to your own requirements as you may not always find ready-made transformers that suit your requirements.

Hope this helps.
Tahmid.

 

[CandleCookie]

Hi Tahmid. Thanks for the site. It really helps me. Do you still have others to recommend? Such as calculations or formulas which I needed?

 

[Tahmid]

Hi,
These are taken from Marty Brown's "Power Supply Cookbook":
Npri = (Vinnom * 10^8) / (4 *f * Bmax * Ac)
Nsec = [1.1(Vout + Vfwd)*Npri] / (Vinmin * DCmax)

f - frequency in Hz
Bmax - flux density in gauss (webers/cm^2)
Ac - effective core cross sectional area (cm^2)
Vfwd - diode forward voltage in V
Npri - primary no. of turns
Nsec - secondary no. of turns
DCMax - maximum expected duty cycle (0-1), if you don't have a reference, 0.95 is good

Hope this helps.
Tahmid.

 

[CandleCookie]

thanks, Tahmid~~

 

[encoder]

Can anyone teach me how to wind the transformer myself. I need a mid-point transformer. For example, this is the core for the transformer.
Ferrite,core,ungapped,EFD25/13/9,2000nH(AL),N87,B66421-G-X187

That is great idea i appreciate you.