All one needs to know about an inductor may be found by applying voltage and monitoring current. I have been using this homemade gadget for a while: big ass MOSFET driven by an appropriate gate driver, 555 timer (with toggle switch to change ranges and trimpot for fine adjustment), low L shunt and bunch of caps to keep voltage stable. 3-rd year EE student could do it (IMHO). OK, one needs to know what s/he is doing as layout does matter. The problem: every time I drop the jig, I have to fix something as assembly leaves much to be desired. Well, not exactly, but it looks ugly. BOM (including PCB) should be between $5 and $20 (depending ob quantities), shouldn't it? Does anybody sell gadget like this? P.S.: It is taken for granted that a lab has oscilloscope and power supply.
inductor tester
Dec 10, 2007
2 Replies
I test inductors with resonant circuits and square wave. I measure the resonant frequency on the scope.
I can add a bias voltage to get core some core detail too.
D from BC
BTDT
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When I only want to know the inductance, I resonate it with a cap and the signal generator via resistor.
Some day I may build a full design, consisting of square wave oscillator, MOSFET switch and current sense resistor.
If you really wanted to get interesting, you could make a free-running oscillator which turns on until the derivative of current change (i.e., d^2I / dt^2) starts rising (saturation), then turn off for a time period corresponding to about 5-10 times the total on period (obtained via an integrator during that cycle).
The rate of rise is sampled (with an analog S&H) and displayed on a meter, while the saturation point (which jointly determines frequency) is displayed on another range.
Hey, that's not a bad idea.
Tim
-- Deep Fryer: A very philosophical monk. Website @
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