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

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  • jong kung
    ... I was wrong when I said 1 millivolt (I think I sent a correction).  It has been VERY long since I thought about ESR meter (sorry).   ST is correct
    Message 1 of 63 , Aug 31, 2011
      >> woops, I forgot the divider. needs to be 1millivolt right?
      >
      > doesn't matter, but should be less than 200mV peak
      > to avoid biasing even schottky diodes.


      I was wrong when I said 1 millivolt (I think I sent a correction).  It has been VERY long since I thought about ESR meter (sorry).   ST is correct (again).

      Feed your output (of arduino) into a voltage divider using 1K resistor (top / first) and 22K resistor (bottom / second).  The output (the middle of the resistors) will be about 1/50 of the input voltage.  Even if you fed it 5 volt, the output would be 0.1 volt (still only 1/2 of 200 mV).

      ====

      To you have LTSpice ?  I can post VERY simple circuit for you to simulate so you can know what I'm talking about (in terns of what the scope will show).

      Or I can just create PDF of the circuit - but then you won't be able to "play" with it.


      Jong











      [Non-text portions of this message have been removed]
    • 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
        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:
        >
        >
        >
        >
        >
        > > 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.
        >
        >
        >
        > =====
        >
        >
        >
        > > 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
        >
        > > 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.
        >
        >
        >
        > Now I'm absolutely no expert on ESR, so if this is really dumb.... 
        >
        >
        >
        > 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).
        >
        >
        >
        > =====
        >
        >
        >
        > > It is a good thing you asked why. Upon review I see I was to
        >
        > > pessimistic the first time around.
        >
        >
        >
        > OK,  I don't fully understand but I'll take some sugar when I can get it.
        >
        >
        >
        > :-)
        >
        >
        >
        > =====
        >
        >
        >
        > > To measure ESR less than 0.33 ohms one could reduce
        >
        > > the size of the 1K resistor to say 100 ohms.
        >
        >
        >
        > (a) is 0.33 ohm realistic value ?
        >
        > (b) swapping 1K down to 100 ohm would probably not work because...
        >
        >
        >
        > ... 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).
        >
        >
        >
        > I think the better option is to change the working freq (the real benefit of using a microcontroller over hardware IC).
        >
        >
        >
        >
        >
        > Jong
        >
        >
        >
        > [Non-text portions of this message have been removed]
        >
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