>> > Can one easily measure the ESR of a capacitor configuration?

>> Yes.

> Russel, then you know why that methode (and usually any cheap and 
> dirty
> methodes you may found on the internet) is not good ?

Let the fun begin.

It's Russell, fwiw.

No. There is no reason per se that this would be so. See below for 
elucidation.

>> There are cheap enough meters to do this for you but you can do it
>> with an oscilloscope, a square wave source and a resistor if you 
>> wish.
>>
>> Here's an example
>>
>>        http://octopus.freeyellow.com/99.html



"All models are wrong. Some models are useful."

The method is entirely usable for getting an indicative value of ESR.
As with any attempt to measure reality, the measurement system is 
imperfect, and it will interact with the system under test, so you 
have to apply both brain as well as test equipment to render the 
results usefully meaningful. The page cited above gives a fair 
indication of the sort of results that can be achieved. Factors such 
as lead inductance (internal and external) and PCB characteristics 
will obviously have a bearing.

There is nothing either magic or lacking in magic about a given 
method, be it cheap and dirty or expensive and polished, being sourced 
from 'the internet' or from some other source. The medium is not the 
message, McLuhan notwithstanding, and to believe so is to deny 
yourself vastly valuable resources. Also, often enough, the price is 
also not always the message (although it can be), and gems can yet be 
found at bargain basement prices.

If you feel that there are limitations to the method that is suggested 
above then a logical thing to do would be to list them and, if you are 
able, to expound on them so that alternatives or improvements can be 
found or devised.

The ultimate test is what the switcher that has the capacitor applied 
sees. Understanding the reasons that a given ESR range is required for 
stability will assist in deciding whether a given ESR test method 
adequately addresses the need. Gargoyle has much to say on stability 
and ESR.

Here's a hot off the press NatSemi design article which addresses ESR 
and switching regulator stability. While its aim is to highlight a 
"new" Natsemi method of decreasing ESR tolerance requirements it does 
give some guide to ESR and stability and is, in any case, interesting 
:-)

        http://www.eetasia.com/ARTICLES/2007MAY/PDF/EEOL_2007MAY16_POW_TA.pdf




            Russell 

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