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I've wound a 5:54 turn transformer. I'm feeding it small voltage pulses in the input, but it seems like on the output, it "struggles" to achieve the output voltage (ie, it doesn't give me square voltage pulses). In the following photos, in green is the transformer voltage in the input and output for your reference.

enter image description here

enter image description here

The load added to the secondary is a resistor, although I've tried having it open circuited and the voltage response is similar. I've also tried using litz wire to see if it helps to output square voltage on the high side, to no results. Does anyone have any idea what might be causing this?

EDIT: Green traces are transformer voltage (primary, then secondary on second photo), and blue is the respective current going in/out of the transformer (primary then secondary again). Apologies yellow and purple are irrelevant to this question. The transformer is an RM12 core, with 24:5:24 turns (sec/prim/sec), so fully interleaved 5:54 transformer.

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  • \$\begingroup\$ Which oscilloscope trace is which, exactly? Also, please show a schematic and a picture of the transformer. \$\endgroup\$ Dec 9, 2022 at 1:42
  • \$\begingroup\$ @JonathanS. Added the requested info in the original post, unfortunately don't have a photo of the transformer available right now, but can post that later on. The circuit is a full bridge feeding +-Vin on the transformer (with some minor dead-time), and I've had connected a resistor on the high (output side). \$\endgroup\$
    – Grigoris
    Dec 9, 2022 at 1:55
  • \$\begingroup\$ Which frequency is your transformer tuned for? If you do Fourier analysis, which frequencies are present in your square wave? \$\endgroup\$ Dec 9, 2022 at 4:30
  • \$\begingroup\$ What are you probing with (particularly the secondary voltage)? \$\endgroup\$ Dec 9, 2022 at 5:47
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    \$\begingroup\$ @Andyaka First appears to be yel/mag = primary ends (green is the difference measured by some diff probe), second appears to be same but with probe across secondary. Is that correct, Grigoris? \$\endgroup\$ Dec 9, 2022 at 19:41

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What you're seeing on the transformer's secondary is ringing due to the transformer's leakage inductance forming a resonant circuit with the parasitic capacitances that are everywhere.

The solution is to dampen these high-frequency oscillations with a RC snubber network, like this:

schematic

simulate this circuit – Schematic created using CircuitLab

I've eyeballed the component values but they should drastically reduce the ringing already, if not eliminate it. R1 will dissipate about 500mW (up to about a Watt). Power dissipation is directly proportional to the size of C1.

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  • \$\begingroup\$ Many thanks for your response. I will try adding a snubber tomorrow in lab. However, apart from the high-frequency ringing, you can notice that the average voltage (imagine the HF ringing gone), that the voltage slowly goes to its final value. It's kind of like it's trying to charge a parallel capacitance, but this being a wire-wound transformer I shouldn't have a problem with parasitic capacitances though? \$\endgroup\$
    – Grigoris
    Dec 9, 2022 at 2:25
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    \$\begingroup\$ @Grigoris I'm pretty sure this is an artifact from the ringing as well. \$\endgroup\$ Dec 9, 2022 at 13:48

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