Purpose of R1 in shunt regulator?

Discussion in 'General Electronics Chat' started by spinnaker, Mar 25, 2010.

  1. spinnaker

    Thread Starter AAC Fanatic!

    Oct 29, 2009
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    MikeML was very nice to post this shunt regulator for me. Can someone please tell me tje purpose of R1?

    A guess is that it limits the date current on the FET but it being tied to the cathode of the TL431 confuses me a bit, unless it is also limiting the current there too.


    The reason I ask is that I do not have any 470 ohm resistors. I have a couple of 240 ohm resistors. Will they do?


    Looks like the Shack carries 470. Hopefully they have them locally but it would be nice to know if I have other options.




    [​IMG]
     
    Last edited: Mar 25, 2010
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    R1 keeps the current through the reference diode (U1) to a safe level. Two 240 ohm resistors will do fine (in series) as a substiturte
     
    Last edited: Mar 25, 2010
  3. spinnaker

    Thread Starter AAC Fanatic!

    Oct 29, 2009
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    Thanks Beenthere.
     
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