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Im glad to be with you. I have question about coupled inductors in altium. I want to make a flyback converter and tried first as in Image 1 Image 1- Circuit . I converted 310V DC to 12V DC as you can see.Image 2-Sim I wrote spice model for T1(Transformer) enter image description here Then, I wanted to ascend my outputs as you see in the Image 4Image 3 -Circuit But sim out came like in Image 5Image4-Sim For 3 output transformer spice code that I wrote enter image description here

What is wrong?. I think 3 output transformer spice model wrong. But I didnt figure out. Give me advice please about that.

With my best regards...

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  • \$\begingroup\$ Ddid spice give any warnings or errors? \$\endgroup\$
    – stark
    Commented Jun 3, 2020 at 14:37
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    \$\begingroup\$ You need to couple all pairs of inducturs, K4 L2 L3 0.99, K5 L2 L4 0.99, etc. LTSpice lets you just do Kx L1 L2 L3 L4 0.99, but Altium's SPICE might not do that (I don't know). \$\endgroup\$
    – The Photon
    Commented Jun 3, 2020 at 16:06
  • \$\begingroup\$ "Ddid spice give any warnings or errors?" @stark No, I I didnt take any error about spice models. \$\endgroup\$
    – GuneyBoss
    Commented Jun 3, 2020 at 16:08
  • \$\begingroup\$ @ThePhoton I added as you said 'K4 L2 L3 0.99 K5 L2 L4 0.99 K6 L3 L4 0.99' and I take 12V. So thank you . But Additionaly I made all grounds -> GND . \$\endgroup\$
    – GuneyBoss
    Commented Jun 3, 2020 at 16:32

1 Answer 1

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What is wrong?

You've made the beginner's error of not understanding the importance of dot-notation when implementing a flyback transformer design. In your first circuit you have, in effect, got lucky with the right output voltage but it's not acting as a flyback converter but more like a regular forward converter and using the transformer as a regular step-down device.

This is not how flyback designs work.

enter image description here

The lower picture shows how I've altered the secondary coil to suit it working as a flyback converter. Flyback converters work by charging the primary coil and reverse biasing the secondary diode then, turning off the primary MOSFET so that "fly-back" occurs and the energy stored in the transformer's magnetic field is released and forward biases the diode. It's a two-phase operation.

Correct use of transformer secondary phase relative to primary phase: -

enter image description here

Notice the change in the position of the dot on the secondary - you can keep the dot as per your original diagram but you then need to connect the secondary diode to the non-dotted end of the secondary (as shown in my amendment to your original diagram).

Picture from A Guide to Flyback Transformers by CoilCraft.

Other reading: Mean Well - Flyback converter: -

enter image description here

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  • \$\begingroup\$ Your answer is very helpful . I understand what flyback transformer means more. I tried my first circuit as you said before. And it worked again but more true:) . But even I change my 3 outputs transformer seconder's dots so their polarities, I didnt take good results. Is spice model wrong? \$\endgroup\$
    – GuneyBoss
    Commented Jun 3, 2020 at 15:08
  • \$\begingroup\$ If your model intends to have a primary to secondary turns ratio of about 45:1 with a coupling of 0.99 then it doesn't look wrong to me. It's very easy to get into a mess with flyback converters and using the zeners on the output(s) is usually a sign of trying to fix something the wrong way. Flyback converters do not require zener diodes on their outputs but they do require absolute critical management of the duty cycle. \$\endgroup\$
    – Andy aka
    Commented Jun 3, 2020 at 15:17
  • \$\begingroup\$ Virtually every spice design I have seen uses separate inductors coupled with "k" components. In micro-cap (my sim tool) when you ad a "k" you specify the inductor names that are coupled and the global coupling factor. Maybe try doing it that way BUT get the simple circuit working correctly WITHOUT the zener then, move on to the multi-secondary version. \$\endgroup\$
    – Andy aka
    Commented Jun 3, 2020 at 15:21
  • \$\begingroup\$ As I searched from the internet I calculated V1/V2 = 310/12 == 25.8 and inductance ratio (N1/N2)^2 =(L1/L2) so 25.8^2 = 667.3 so I gave for my first circuit sec inductance 2uH(random) then for 667.3*2 =~ 1.3m . And it was true as we understand from sim. But for 3 output transformer I gave 1.3*3 = 3.9m to primer and sec's stayed same 2uH. Coupling factors 0.99 for both circuits. \$\endgroup\$
    – GuneyBoss
    Commented Jun 3, 2020 at 15:40
  • \$\begingroup\$ I tried my circuits either altium sim or ltspice , First circuit worked, but 3 output didnt. \$\endgroup\$
    – GuneyBoss
    Commented Jun 3, 2020 at 15:47

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