Naftali is correct in that Kelvin is an extension of °C, only offset so that
0 Kelvin is at
absolute zero, or -273.15 °C. When referring to a Delta-T, the number is
the same
whether in Kelvin or °C. Be aware that the specs noted are Delta-T/Watt,
not actual temperatures.
Also, Theta JS is Junction to (heat)Sink. I don't know what a solder-point
is. Please enlighten.
I have not worked much with SMT, so I may be showing my age.
John Shinn, P.E.
-----Original Message-----
From: N. Shani
Sent: Tuesday, October 09, 2012 3:22 PM
To: McInturff, Gary
Cc: [email protected]
Subject: Re: thermal resistance - K versus C
K or C are (almost) identical, just the starting point is different: C
starts @ 0 (freezing temperature for distilled water at sea level
pressure, i.e., 1 atmosphere), and defines 100 as boiling of same
conditions.
K is the same as C, but is off-set by 273 (i.e., 0 K is -273 C, so 100
C is 373 K).
What transformation did you use to get those weird numbers?
Cheers,
N. Shani
Ottawa, ON
On 10/9/12, McInturff, Gary <[email protected]> wrote:
Thought I knew what I was doing, obviously I don't
I have a device with a thermal resistance ThetaJA (J-P in this
documentation). It's for SMT CHIP LED the specified value is 400C/W. for a
plastic package that seems about right. I am looking at another LED but
it
lists ThetaJA as 400K/W. (Kelvin/Watt) Seems pretty good as it would
convert to 126C/W - the lower the better. But then I converted the ThetaJS
(I think its junction - solder point), and that value was 180K/W. When
converted its -93C. Does the change in sign just indicate the direction
heat
is flowing? ThetaJA is positive since the heat is leaving the die through
the package, and the ThetaJS is negative because it is heating entering
the
die through the solder process?
Gary McInturff
Reliability/Compliance Engineer
Esterline Interface Technologies
Featuring
ADVANCED INPUT, MEMTRON, and LRE MEDICAL products
600 W. Wilbur Avenue
Coeur d'Alene, ID 83815-9496
Office:208-635-8306
Cell: 509 868 2279
Toll Free: 800-444-5923 X 1238
[email protected]<mailto:[email protected]>
www.esterline.com/interfacetechnologies<http://www.esterline.com/advancedinput>
Technology, Innovation, Performance...
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