Cheap way to measure leakage inductance accurately?

[Flyback]

Hello,

We need to be able to measure the leakage inductance of our SMPS flyback transformers..however, we do not have an LCR meter accurate enough to do this. (all we have is an LCR40 meter by peakelec.co.uk)

Therefore, we wish to measure leakage inductance by the “resonance method” (as in the below schematic and LTspice simulation)

Method of measurement:
We will simply short out the secondary in the usual manner when measuring leakage inductance, and then add a capacitor in parallel with the primary, then we have an LC tank circuit, and we will switch some current into it, and then switch the switch off, and it will then ring at the LC resonant frequency, …from this frequency, we will calculate the leakage inductance……do you think this is accurate enough?….we will observe the ringing on our TDS1002 scope.

We will trust the LCR40 to be able to measure the 100nF capacitance very accurately, since cheap LCR meters always measure capacitance far more accurately than inductance, do you agree?

Is our measurement method accurate?

TDS1002 scope
https://courses.washington.edu/phys33...UserManual.pdf

LCR40 LCR meter:
https://www.farnell.com/datasheets/1692006.pdf

(also-does leakage inductance measure higher or lower when the measurement frequency is higher?)

 

[ronsimpson]

I have a low cost LC meter that makes a oscillator by using a unknown (L or C) and a known (C or L). It then measures the resonant frequency and does the math to find the unknown value. I can measure the inductance of 1" of wire with this $100.00 meter. The schematic is in the internet and probably this forum.

 

[Flyback]

Thanks, i suspect your idea is along the same lines as mine above....and I think even very cheap LCR meters measure capacitance accurately, even low values like 10nF.....so we can use the resonance method to get the value of L accurately, even if L is small, like 1uH?

 

[moffy]

Your method is the best, very simple and straight forward.