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Re: [Electronics_101] Re: LCD TV Power Supply Woes

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  • jong kung
    ... 100 Khz is what the capacitor manufacturers use to measure the ESR.  That s what I read - so everybody tries to use that freq.  But I ve seen freq as
    Message 1 of 63 , Aug 31 1:18 AM
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      > Don't matter 50kHz would be close enough.



      100 Khz is what the capacitor manufacturers use to measure the ESR.  That's what I read - so everybody tries to use that freq.  But I've seen freq as high as 500Khz on pre-made ESR on Ebay this week.  So it is NOT critical.

      Higher freq just allows for testing of smaller capacitors. Even with 100 Khz, I think you can go down to something like 0.00001 microfarad capacitor (I probably got the zeros wrong - but you get the idea).


      Jong











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    • ae5ew
      5mv/div for vertical input would be considered good. You must have good grounds in order to get meaningful measurements at 5mv/div. That is with a 1x probe.
      Message 63 of 63 , Sep 1, 2011
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        5mv/div for vertical input would be considered good. You must have good grounds in order to get meaningful measurements at 5mv/div. That is with a 1x probe. 10x probe would be 50mv/div.
        Charles AE5EW

        --- In Electronics_101@yahoogroups.com, jong kung <jongkung01@...> wrote:
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        >
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        > > No because of the sensitivity of the measuring instrument.
        >
        > > The OP said he had a Heathkit oscilloscope. Say the
        >
        > > oscilloscope had a sensitivity of 5 mV/cm.
        >
        >
        >
        > Did he say that (I missed it then) - or is that a ball park for old scopes.
        >
        >
        >
        > =====
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        >
        > > Next I estimate the signal source amplitude at the output
        >
        > > of the micro controllers is 3 volts peak to peak. For a 10 ohm ESR.the
        >
        > > output signal is approximately 20.6 mV peak to peak For a 1 ohm ESR
        >
        > > the output signal is approximately 3 mv peak to peak. For a 0.33 ohm
        >
        > > ESR the output signal is approximately 1 mV peak to peak. Hence the
        >
        > > output signal will be less than 1 mV peak to peak for a ESR less than
        >
        > > 0.33 ohms. I doubt if a meaningful measurement can be made with a
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        > > signal amplitude less than 1 mV peak to peak.
        >
        >
        >
        > Oh man... I have to go back and crack open my old text book on Freq & capacitors.
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        > Now I'm absolutely no expert on ESR, so if this is really dumb.... 
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        > Isn't 3 ohms about good enough for ESR meter ?  Aren't we looking for
        > higher ESR (because most likely the failed capacitors are
        > electrolytics).  Translated in other words, below certain low ESR, the
        > trace on the o-scope will be basically flat (good).
        >
        >
        >
        > =====
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        > > It is a good thing you asked why. Upon review I see I was to
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        > > pessimistic the first time around.
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        > OK,  I don't fully understand but I'll take some sugar when I can get it.
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        > :-)
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        > =====
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        > > To measure ESR less than 0.33 ohms one could reduce
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        > > the size of the 1K resistor to say 100 ohms.
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        >
        >
        > (a) is 0.33 ohm realistic value ?
        >
        > (b) swapping 1K down to 100 ohm would probably not work because...
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        >
        >
        > ... because that makes the voltage greater than diode forward V and the
        > capacitor won't be isolated from the rest of the circuit (translation:
        > the capacitors then has to be removed from the circuit).
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        >
        > I think the better option is to change the working freq (the real benefit of using a microcontroller over hardware IC).
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        > Jong
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        > [Non-text portions of this message have been removed]
        >
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