Re: Where are all the ESR meters?

On Mon, 23 Jul 2007 05:50:10 -0700, Winfield <winfieldhill@xxxxxxxxx>
wrote:

On Jul 23, 6:08 am, Fred Bloggs <nos...@xxxxxxxxxx> wrote:
John Larkin wrote:
On Sun, 22 Jul 2007 19:39:36 GMT, Fred Bloggs <nos...@xxxxxxxxxx>
wrote:

John Larkin wrote:

On Sun, 22 Jul 2007 15:57:37 GMT, Fred Bloggs <nos...@xxxxxxxxxx>
wrote:

Jim Thompson wrote:

On Sun, 22 Jul 2007 04:24:21 -0700, Winfield <winfieldh...@xxxxxxxxx>
wrote:

Jim Thompson wrote:

Winfield wrote:

I'll post mine, when I get enough energy to transcribe
it from my paper scratchings, calculations and notes.
Remember, it must be four terminal, and handle high DC
voltages when probing in-circuit storage capacitors.

How high is "high"?

Perhaps a better question is, how big is big?

Several designs we've been considering have a
pair of diodes to discharge the test capacitor
and limit the circuit voltages, but I've heard
these can fail with large, charged capacitors.

I think the issue isn't necessarily how high
the voltage (tube amplifiers get to hundreds
of volts), or how high the current delivered,
but how much energy is going to be dissipated
in the protection components that discharge
the guilty capacitor.

I'd say the answer is, the size of two fists.
I think we're talking about ~ 100J of energy.
Isn't that more than enough to blow out a
common glass diode and/or a 1/4-watt resistor?

Should be enough to crank you over a few times ;-)

...Jim Thompson

WH is stalling... input protection has little to do with a basic
measurement architecture. I had no idea this little project would be so
difficult for everyone:-)

Interesting that for a proposed "group design", hardly anybody is
willing to make a first step. The psychology of group design is
fascinating, and it turns out that an audience is a huge inhibition;
people tend to not expose ideas if they fear they are imperfect, and
might give some nit-picker grounds for public criticism.

Brainstorming is delicate because people are fragile. At my place, we
scribble goofy ideas on a whiteboard, do a lot of stupid stuff (don't
distinguish between circuit-as-proposal and circuit-as-joke), argue
and laugh a lot, and sometimes come up with brilliance, with no way to
tell who gets the credit. Some people just can't play at this game.

John

Well whatever...the task is straightforward and does not require a great
amount of ingenuity. The ingenuity comes in deciding the functionality
of the meter. In my opinion there is nothing to accomplish by going half
way to an impedance analyzer, there are already plenty of compact and
fully functional products in that niche. The key is to produce the
simplest possible design that measures ESR, if something else comes free
along with that without introducing one iota more of complexity then
fine, but if it requires one speck of dedicated hardware not useful for
determining ESR then it goes. This will require that you discover
something inherent to ESR that allows for a very simple circuit
architecture. That is all the help I am going to give you at this stage:-)

Thanks for the excellent illustration of my point. You are far more
concerned about your ego than you are about the technology. Probably
that explains why you don't design electronics.

I know where you're coming from with that statement and it is not true.
I am far enough along to know for sure whether something will work or
not. All you have thought of so far is measuring the in-phase component
of voltage developed by a current pulse. And your typical white board
brainstorming is largely used for the how and not the what. The idea
within the original Italian hobby circuit was not too bad, the execution
was lacking, and the outputs of interest were sort of compressed, but
the idea of a bridge driven by a reasonably *low* impedance current
source, resulting in short transient recovery from the ESL and limited
peak response, is not bad at all.

A better idea, I think, is to use a proper higher-impedance
current source, and drive with a 100kHz sine wave, thereby
greatly reducing the ESL problem, which can otherwise be a
killer for the 1 to 30 milliohm region. Using a sine wave
also means the measured ESR can be compared with laboratory
meter readings. Otherwise, how would one compare sets of
square-wave readings with accurate lab instrument readings?

I'm thinking of using a 2-volt peak sine wave with a 200-ohm

2-volt P-P is too high to do in-circuit testing in all cases as it
could cause Si junctions to conduct. 0.2V or 0.3V would be a lot
better.

resistor (10mA peak test current) delivered from a rail-to-
rail opamp with a slew rate exceeding say 2V/us. I'll break
the resistor into three parts and add two sets of protection
diodes to the rails. The outermost resistor can be a 100-ohm
10-watt high-thermal-mass part to discharge the capacitors.

Some of the designs out there don't bother with discharging the
capacitor- they put a low (and stable) -ESR cap of a few uF in series
with the DUT. That way you have an upper limit on the energy to be
handled (given an upper limit on the voltage of (say) 400VDC or 500VDC
to handle off-line filter caps).


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@xxxxxxxxxxxx Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
.

Relevant Pages

  • Re: Where are all the ESR meters?
    ... John Larkin wrote: ... voltages when probing in-circuit storage capacitors. ... Interesting that for a proposed "group design", ...
    (sci.electronics.design)
  • Re: Where are all the ESR meters?
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  • Re: Where are all the ESR meters?
    ... voltages when probing in-circuit storage capacitors. ... determining ESR then it goes. ... resistor delivered from a rail-to- ...
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  • Re: Where are all the ESR meters?
    ... Jim Thompson wrote: ... voltages when probing in-circuit storage capacitors. ... Interesting that for a proposed "group design", ...
    (sci.electronics.design)
  • Re: Where are all the ESR meters?
    ... Jim Thompson wrote: ... voltages when probing in-circuit storage capacitors. ... Interesting that for a proposed "group design", ... determining ESR then it goes. ...
    (sci.electronics.design)