Re: Looking for a better in circuit ESR meter


Chuck Harris
 

You can always take the engineer's way out, and use your scope (OS)
and a function generator (FUNC).

......................................
FUNC o)=======@.......................
......|.......|.......................
......|......10K......................
......|.......|.......................
OS...o)=======@============@===========> To cap
......|....................|..........
......|................. DIODE........
......|..................CLAMP.......@=>
......|....................|.........|
.....///..................///.......///

Set the function generator to 100KHz, and 10Vpp, and set your scope
to external trigger on the function generator's trigger output.

The head to tail diode clamp will protect your circuitry from over
voltage by the function generator, and the scope will show a P-P
signal that represents the ESR. Since the current into the cap is
1ma, ESR is easily calculated from the P-P voltage measured.

Slow the function generator down to a point where Xc dominated the
impedance, and you can calculate the capacitance from the voltage.

It is ground referenced, so make sure the DUT isn't plugged into
anything that is grounded.

The idea is, of course, gratuitously stolen from others...

-Chuck Harris

Reginald Beardsley via groups.io wrote:

Does anyone have any experience with the B&K 881? It appears to provide the same testing as the EDS-88A for about $75 less. In fact looks like an outright copy with minor changes. Of course, that does not mean it is any good.

I'm dealing with a SMPS which has caps in parallel with a resistor and a diode. All crammed into a very small space. Both the Arduino based BSIDE ESR02 Pro and the Peak atlas ESR70 can't deal with the diode and resistor and produce similar <100 pF answers. From looking at the output on a scope I think both are turning the diode on.

Reg



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