SMPS foil transformer

Discussion in 'The Projects Forum' started by jm-a, May 4, 2013.

  1. jm-a

    Thread Starter Active Member

    Oct 20, 2010
    Hi all,

    I plan to build a smps foil transformer, and i'd want to clear some questions.


    - need n x 2 halves cores with no gap?


    - i'm going , to '' stack '' these cores, Al value?

    E 65-32-27 with coil former E65

    According to '' Epcos tools '', resulting Al is sum of n x Al core

    As usual, thanks a lot.

    Last edited: May 7, 2013
  2. bountyhunter

    Well-Known Member

    Sep 7, 2009
    You got no responses because nobody understands what you are asking. I used to make transformers for switchers and I don't understand what you are asking.

    There is no such thing as a "foil transformer", some transformers use foil secondary windings instead of wire when their current is very high. Since you have not specified what electrical specs the transformer must meet, it is impossible to design a transformer.
    jm-a likes this.
  3. jm-a

    Thread Starter Active Member

    Oct 20, 2010
    Hi all,

    Firstly, of course, thanks to bountyhunter for his reply.
    Don't worry, i agree with your content.....

    So I'm going to describe more obviously, what i try/want to get:)

    Need: power supply 10 > 30 -40 VDC with 20 A continuous not peak

    Schematic from this site:

    Schematic of modifications:


    Questions 1 to 3:


    1 : As now i plan to use a full-wave rectifying unit - 4 x DSEP030-12AR -, where to connect '' power ground '',seen top left of this schematic?

    2 : voltage range needed: 10 > 30-40 VDC so, must modify resistor values of 27 K, 100 K, 6,8 K?

    3: I have already an auxiliary power supply card with 15 V output, and sufficient power; of course, i want to use it, so must change resistor values of 220 Ohm with BD139 and 140?

    Googled and googled a lot , and found following components:

    - NTC from EPCOS B5736450109M006

    View attachment E112300_1_TD.pdf

    - Bridge rectifier KBPC35

    View attachment Bridge.pdf

    - ''2nd bridge'' rectifier 4 x DSEP30-12AR

    View attachment A400_DSEP30-12A_IXY.pdf

    - IRFP460

    View attachment A100_DS_IRFP460APBF.pdf

    - Gate drive transformer

    Murata products: 76602/1C or 1026C or better choice?

    Coilcraft products: SD250-3L

    I have downloaded maximum items, so can't link them:(

    As usual, right choice or not?

    Last question, about output filter L - 33µH value - , with a full wave rectifying unit, it seems have read - maybe a mistake as smps is hot stuff - , ripple is doubled?

    I choose a full wave unit to avoid center tapped transformer, for easier building with cooper foils, and kapton tape to insulate between layers.

    For 50 Khz skin depth ≈ 0,3 mm - 10 mil - so would build it with 0,5 mm thickness foil - 20 mil -

    5 A / mm2 - 5A / 1,07 x 10 ^-5 sqr foot - > foils height ≈ 1.57 inch for high safety margin.

    Hence my questions:
    - about '' stacking '' n half cores, to know resulting Al, even if it was honestly bad described!!!!! Found

    - for a transformer, no gap permitted > wasting too much energy Found

    - inductor like in flyback: gap needed to store energy, than discharging it when ''no-conduction'' from switches. Found

    So back on output filter, identical value or to change also?

    This post is a long one, i hope it is more obvious than previous.

    Thanks to all.

    Last edited: May 7, 2013