ESR tester

There is no need to. A power supply and DC load are all you need. Some power supplies can also sink current so you wouldn't need the DC load.

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How would that work?

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John Larkin         Highland Technology, Inc 

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Would be simple to build but how much could you get for it? would you buy one?

use something like a vnd14nv04 and it should be more or less bulletproof

-Lasse

Charge the cap and set the DC load to the current you want to test with. Basically what you do with your circuit.

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Failure does not prove something is impossible, failure simply 
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nico@nctdevpuntnl (punt=.) 
--------------------------------------------------------------

I see a linear discharge. What's regulating the current?

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Suppose the cap is 1000 uF with ESR 10 milliohms.

Apply 10 amps, and the ESR step is 100 mv.

The C part of the cap is ramping at 10,000 volts/second. That's 100 mv in 10 microseconds. So to measure the ESR accurately, you'd better apply the current step and measure the jump in well under a microsecond. Can you "set the DC load" that fast? Or program a

4-quadrant power supply to do that?

I think it devolves to the idea that you have to measure the ESR a lot quicker than the cap's internal tau, namely C * ESR. I'm seeing a current risetime of about 100 ns.

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John Larkin         Highland Technology, Inc 

jlarkin at highlandtechnology dot com 
http://www.highlandtechnology.com 

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom laser drivers and controllers 
Photonics and fiberoptic TTL data links 
VME thermocouple, LVDT, synchro   acquisition and simulation

the fet? the datasheet shows ~5A for 5V gate drive

-Lasse

The voltage drop in the source resistor makes the mosfet pretty much a constant-current sink. I monitor the source voltage with a scope, the yellow trace, and adjust the pulse generator voltage to get my test current, 5 amps in this case.

The initial jump (blue trace) is ESR and the slope is C. Those calculate out to 22 milliohms and about 1440 uF, for a 1500 uF labeled electrolytic. Not super accurate, but good enough to quantify ESR.

A better version would do proper closed-loop control of the current.

I recall a thread with Win Hill about something similar.

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John Larkin         Highland Technology, Inc 

jlarkin at highlandtechnology dot com 
http://www.highlandtechnology.com 

Precision electronic instrumentation 
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Custom laser drivers and controllers 
Photonics and fiberoptic TTL data links 
VME thermocouple, LVDT, synchro   acquisition and simulation

For a couple hundred dollars, sure. You'd sell some at $500. There are a lot of people designing stuff that cares about ESR, and lots of parts without ESR specs.

Cute part. But kinda slow for this app.

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John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
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. . . .

I made a simpler setup recently for measuring ESR. It's not as sensitive as yours, but it's calibrated and uses fewer parts: .-. .- 1k | | | >-----/\/\/----+--->

-' '-' | --- d.u.t. 10V p-p --- | | ===

You could use a 50-ohm generator directly. That saves a resistor and gets 20x more signal...

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Cheers, 
James Arthur

Nice documentation. How does this number compare to the standard ESR meter that uses

100kHz? Were the spikes in the scope trace true inductive kick, or artifacts being injected into the monitoring system?

I've done that with a 50 ohm generator, for testing tantalum caps with hundreds of mohms ESR. But at ~~10 mohm levels, the signals get really small.

There are, incidentally, some amazing fets around these days, or at least amazing fet specs. IRF3805 is a 55 volt D2PAK part with a rated pulse current of

890 amps. So it will switch 49 kilowatts, on paper.

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John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
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VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators

I don't know, but I don't trust any spot measurement done at a single frequency, especially on any affordable meter.

I think the spikes are from real ESL. But some may be in the board itself. I'm guessing I have a milliohm or two of extra ESR, too, in the traces. I should move the signal pickoff wire to the right, and maybe add some vias to the back side copper.

Based on the 500 mV spike, assuming 5 amps in 100 ns, a rough estimate of the ESL of that cap is 10 nH.

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John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
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Multichannel arbitrary waveform generators

Grab a few different LC meters and measure some electrolytic caps and iron-core inductors. The numbers will be all over the place.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators

At Semco, where silver mica was the main product line, there was three different instruments for doing value and Q testing caps in the lab. Two of the brands I remember as GenRad, and a motorola unit that was suppose to be the cream of the crop. The third unit I can't remember the brand but that apparently was to hard to work with.

Any way, all three of these units would not agree with each other as to Value and Q for the CUT. And this was when each of these units were sent to calibration labs for alignment and certs.

The motorola and third brand used a pulse method to obtain Q. The Genrad used an analog offset method where as you first zero the unit by shorting the test terminals, zero the vernier, then zero that for a reading on the needle, then zero Q null. When you test, you moved the freq dial to find null, this gives the cap value. You then adjust the Q dial, which was nothing more than a pot, to fine null for that, and that has a marker dial which aided in calculating the Q factor

The GenRad was the instrument of choice Q testing.

Basically what all this means is, each method of use may give you different results, so which one do you use?

Jamie

Interesting.

Probably a modern, digitized and multi-processed (by various means, CPU DSP FPGA, etc) automated piece of gear from Agilent. would give you a plotted output over frequency.

frequency,

Quite some years ago, I made some measurements of capacitor ESR and ESL using an HP3577A network analyzer. For some electrolytic caps of geometry similar to yours, I found ESL values of 4nH, which is pretty damn good. It surprised me at the time, as I'd always been told that Al electrolytics were no good at RF, because too inductive. Ta capacitors weren't significantly better than Al caps, except perhaps for overall size, and then only sometimes.

Axial-lead caps were terrible, exceeding 100nH in some cases. That's fine for filters in mains power supplies, but don't even think of using them in wideband or fast circuits.

Jeroen Belleman

[snip]

iron-core

One area where I have found large differences is how low-Q inductors and capacitors are handled. The better instruments measure both in phase and quadrature impedance, and compute inductance/capacitance and D or Q. The worser instruments measure the magnitude of the impedance, ignoring phase, and so are badly fooled by non-ideal components.

The simple test is to put a high-Q inductor or capacitor in series with a potentiometer, and see if the instrument's report of inductance or capacitance is much affected as one varies the series resistance.

Joe Gwinn

frequency,

I'm

back

I was also kinda amazed by the very low ESLs of aluminum and tantalum caps. Polymer aluminums are really good too, super low ESR, but only come in low voltages and capacitances.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators