# Is this an Impedance Matching Curve?

This may be a very quick answer, I had a test that was set up like this. The primary inductance of the transformer was roughly 0.022H and the inductance of the secondary of the transformer was 0.045H. The transformer uses those iron/silicon steel laminations. The resistance of the primary coil is 0.4 Ohms and the same for the secondary coil. I dont know what the leakage inductance is unfortunately. The transformer ratio was 1.35. simulate this circuit – Schematic created using CircuitLab

I was just experimenting and trying some stuff out as in this experimental set up shown and I basically just swept the frequency from 1Hz to 2kHz and measured the voltage at the point shown on the output side. The graph I got was this: I was wondering if anyone could tell me what they think about this graph. At first glance to me it looks like an impedance matching curve where the Y-axis is a voltage instead of the impedance, I cant seem to get the simulation to give me the same answers though but I don't normally use circuit lab....

I have a bunch of these transformers I wound a while back and they are all different but they all seems to have a max voltage on that output around the same frequency of around 200Hz on a Squarewave and 400Hz on a sine wave (obviously one is basically double the other), is it a transformer material thing?

Are my results consistent with impedance matching situation?

• So, is L2 (45 mH) the leakage inductance? When you say 8 mF do you mean 8,000 uF? – Andy aka Feb 20 '20 at 12:54
• Hey Andy, No L2 was just supposed to represent the actual inductance of the secondary on the transformer because circuit lab doesn't let you add a secondary inductance. I assume it calculates it using the turns ratio - maybe I should delete it. With the capacitors yes that's right – NROC Feb 20 '20 at 12:58
• Are you measuring from your cap to your ground, or from one side of the cap to the other? The secondary side isn't referenced to the primary ground. – Cristobol Polychronopolis Feb 20 '20 at 13:06
• Well, if 45 mH is the secondary inductance (primary disconnected) then you shouldn't model it at this value - it might be in the region of 1 mH. – Andy aka Feb 20 '20 at 13:07
• So you've told us it's a step-up transformer but not much else about it, and as Andy says, L2 is probably in the wrong place. Turns ratio, winding resistance and leakage inductance would be useful information, but "any thoughts" is too vague to be a question. – user_1818839 Feb 20 '20 at 13:12

## 1 Answer

So I retried the simulation using a 80uF capacitor in parallel to the transformers output and I appear to now be getting roughly the same curve although circuit lab spits it out using log on the x axis simulate this circuit – Schematic created using CircuitLab

This is the simulation result: So that seems to be accounting for the curve i see experimentally but could someone please point out what is happening here? Its starting to look like the secondary coil is being driven into resonance by the primary coil....

Thanks