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In my power supply design I am tested switching operations of half bridge circuit with open circuit and observed clear 155, -155 square wave I want to test step by step so for next step I want to implement to circuit a own build magnetic components (resonant inductor and transformer). Since this is my first time doing magnetic component I don't know how circuit behaves to magnetics. For example I try the test transformer with connect to 50 Hz variac primary of my transformer and give little bit AC signal I see current is getting higher and higher when I increase input voltage via variac and vibration noise is increasing with it (I guess its because of transformer is gapped and gaps is not very tight). With this test I can't observe if my winding ratios are good or not because input voltage can't observe since primer is like short circuited. I am stuck there. Any recommendation?

Firstly transformer is 3c94 ferroxcube ETD54 material. 21 primary turn and 11 secondary turns transformer is center tapped 3 winding. I give 0.75 gap with tape. 50kHz-150kHz working frequency. 75kHz resonant frequency 65 uH desired Lm (mutual inductance). I found LCR meter from friend and trying to test measure inductances: Primary Side inductance (secondary opened): 153 uH. Secondary 1 inductance:47 uH. Secondary 2 inductance:47 uH. I don't quite understand it looks like wrong. I will send picture of how i wind the bobin maybe I did mistakes.

Winding structure, 2 layers inside of bobin is secondarys. Outside is primary.

enter image description here

enter image description here

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  • \$\begingroup\$ Please state inductor and transformer core cross section area, material and number of turns. \$\endgroup\$
    – winny
    Commented Jun 1 at 18:17
  • \$\begingroup\$ @winny I editted post. Thanks. \$\endgroup\$
    – MSB
    Commented Jun 1 at 18:27
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    \$\begingroup\$ And your switch frequency? \$\endgroup\$
    – winny
    Commented Jun 1 at 20:26

1 Answer 1

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I am stuck there. Any recommendation?

The simple answer is get an LCR meter. Mine cost around £150 from Farnell and I would not be without it when winding my own transformers (which I do a few times a year). This is what I use and I'm very happy with it: -

enter image description here

Image from Farnell. If you are serious about designing this type of converter, you have to get the right equipment or else you'll never really get a grip to what your leakage inductance is and you'll be left scratching your head for hours and hours so, how much do you value your time?

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  • \$\begingroup\$ In LCR meter how much henries this devices can measure sir. I take a look datasheet only see levels like 2mH/20mH etc. For example can I measure 20uH with 2mH level of LCR. I was think I can't measure thats why I am searching for good devices and they are not effordable. \$\endgroup\$
    – MSB
    Commented Jun 1 at 12:32
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    \$\begingroup\$ @MSB page 12 of the data sheet says it can measure 20 uH with a resolution of 1 nH using the 100 kHz test frequency. Page 12 gives you all the ranges. \$\endgroup\$
    – Andy aka
    Commented Jun 1 at 15:41
  • \$\begingroup\$ @MSB if we are done here, please take note of this: What should I do when someone answers my question. If you are still confused about something then leave a comment to request further clarification. \$\endgroup\$
    – Andy aka
    Commented Jun 3 at 15:47
  • \$\begingroup\$ Hello, I am actually using LCR with your recommendation. But I don't quite understand why measurements are not right. Since the ratio of transformer is 21:11:11. Primer:Seconder1: Seconder2. Aren't the inductances should match this ratio \$\endgroup\$
    – MSB
    Commented Jun 3 at 17:16
  • \$\begingroup\$ I share winding structure and I am trying New winding strategy, s1:P1:S2:P2. With 2 primary because of the wires having a hard time to fitting. I will share results after I finish. Trying new structure because my other structure dosnt looks right to me but maybe I am missing some point \$\endgroup\$
    – MSB
    Commented Jun 3 at 17:19

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