Yesterday I was building an LCR meter which wasn't functioning correctly. After some researh online I found that the self reasonant frequency of inductor has a part to play as well. If I understood the video correctly, the self reasonant frequency is basically the frequency where the inductor stops functioning without being connected to any other components. According to the specs from Farnell, my inductor only has a reasonant frequency of 1K. oops
The problem is I built lady ada's minty boost phone charger with an inductor I don't have the spec for. How do I know the self resonant frequency is correct? I have had stability issues with the circuit before. I suspect the inductor is pants.
Best Answer
The inductor doesn't "stop functioning", it just starts to look capacitive at frequencies above the SRF. Must be a pretty big inductor to have such a low SRF (I'm assuming you mean 1kHz)
Ideally you would test with a network/frequency analyser, but you could build an LR filter with it and use a function generator to pass a sinewave through it and look for the sharp drop in output at the resonant frequency. Or do similar with an LC tank. Or use a 2-channel scope and look for the phase change.
L1 has 200nF capacitance in parallel with it an 10Ω series resistance (not shown - set up in the inductor specs to achieve the approximate 1kHz SRF)
Simulation:
I'd also grab a new inductor with a higher SRF, as you're going to have to do this anyway.