"Normalised drain-source on-state resistance"

Discussion in 'General Electronics Chat' started by JMD, Jul 13, 2010.

  1. JMD

    Thread Starter Member

    Dec 9, 2009
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    I came across a characteristic i didnt understand fully.. "Normalised drain-source on-state resistance". This value can easily differ more than a factor 20 from the RDS(ON).

    Take a look at this datasheet: http://www.datasheetcatalog.org/datasheet/philips/PHB_PHP_PHW45NQ10T_1.pdf

    So what is RDS(ON) compared to "Normalised drain-source on-state resistance"? What is the normalized?

    Thanks in advance :)
     
  2. Dx3

    Member

    Jun 19, 2010
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    The horizontal axis on that chart is labeled, "Junction temperature". The On-state resistance of that transistor can vary from .65 times its resistance at 25 C to 2.7 times its resistance at 25 C as the temperature changes, and I call that about a 4 to 1 ratio.

    Whatever you calculate for an Rds-on at room temperature, expect the transistor to warm up and have more resistance...up to 2.7 times as much as it has at room temperature.
     
  3. JMD

    Thread Starter Member

    Dec 9, 2009
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    And the vertical reads "Normalised On-state Resistance" - resistance is in Ohms. What you say is, that its a multiplier. If what you say is true, the vertical label makes no sense. It should have said "On-state Resistance multiplier" instead. Or is this what they call "normalized" ??
     
    Last edited: Jul 13, 2010
  4. Markd77

    Senior Member

    Sep 7, 2009
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    That's pretty much what normalised (or normalized) means. It's all relative to 1 at 25 degrees.
    They have done it because Rds on is also dependant on some other things, like gate voltage.
     
  5. JMD

    Thread Starter Member

    Dec 9, 2009
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    Now that you say it.. youre right.. thats what normalized means. But that vertical title still doesnt make sense :) Thanks for the answers!
     
  6. Dx3

    Member

    Jun 19, 2010
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    Datasheets can be a PIB to read. You have to suck every bit of information out of every label to get them to make sense.
     
  7. Jony130

    AAC Fanatic!

    Feb 17, 2009
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  8. JMD

    Thread Starter Member

    Dec 9, 2009
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    Thanks for all the answers :) Was just what i needed.
     
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