# "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?

2. ### Dx3 Member

Jun 19, 2010
87
7
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
96
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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
96
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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
87
7
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.

Feb 17, 2009
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8. ### JMD Thread Starter Member

Dec 9, 2009
96
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Thanks for all the answers Was just what i needed.