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02-24-2013, 08:38 PM #1
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justinjja
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PT54 Help

In the datasheet the max junction temp is 80c

I found the Leds on chip Thermistors B value to be ~3400
and its 25c resistance is 10k omhs

Based on that I can find the Thermistor temp

But I couldnt find a (Degree/Watt) number
connecting the Thermistor temp to the junction temp

any ideas?

http://www.mouser.com/catalog/specsh...phlatlight.pdf

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02-24-2013, 11:48 PM #2
 Class 3B Laser Join Date: Feb 2008 Location: Lincoln, NE Posts: 2,991 Rep Power: 216
Meatball
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Re: PT54 Help

You need to know three data points, which are given here in the NTC datasheet:
Search Engine | ?????
^^Translate into English if necessary

You use the appropriate constants in this lovely little gem:
Steinhart?Hart equation - Wikipedia, the free encyclopedia

You could also just collect those data points yourself and use an online calculator:
Steinhart-Hart Thermistor Calculator
Thermistor Calculation Examples
Capgo - Thermistor Calculator

This is a really nice one: Calculators for Temperature and Thermistor Applications

Check out the section titled "B or β parameter equation"
Thermistor - Wikipedia, the free encyclopedia

^^I think the datasheet has everything you need to use that simpler linear approximation.

That should give you a push in the right direction.
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02-24-2013, 11:52 PM #3
 Class 2M Laser Join Date: Mar 2011 Location: Texas Posts: 692 Rep Power: 51
justinjja
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Re: PT54 Help

Thanks, but that all deals with the thermistor,
I need info on the LED
Most devices like this LED would have a rating that relates the case and junction temp in relationship to wattage

EDIT:

Found it on the Luminus webpage,
1 degree c/w
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Last edited by justinjja; 02-25-2013 at 12:23 AM.

02-25-2013, 04:54 AM #4
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Meatball
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Re: PT54 Help

Oh. Ermmm.

I missed that whole "junction temp" bit. Sorry about that.

Good luck on your project!
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02-25-2013, 08:59 PM #5
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BShanahan14rulz
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Re: PT54 Help

Specification | Murata Chip NTC Thermistor Output Voltage Simulator | Murata Manufacturing Co., Ltd. go here for info on how to use murata's characterization tool for NCP15XH103J03RC.

page 6 on the datasheet you linked shows the thermal resistances between the points of interest. It also gives you an R0j-ref, were thetaj denotes junction and ref denotes reference point. This is the thermal resistance between chip and thermistor location, and I believe is in the units you are looking for, at 0.94.

edit: I see you found already, that it is ~1.

Last edited by BShanahan14rulz; 02-25-2013 at 09:00 PM.

02-26-2013, 04:55 AM #6
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justinjja
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Re: PT54 Help

Quote:
 Originally Posted by BShanahan14rulz Specification | Murata Chip NTC Thermistor Output Voltage Simulator | Murata Manufacturing Co., Ltd. go here for info on how to use murata's characterization tool for NCP15XH103J03RC. page 6 on the datasheet you linked shows the thermal resistances between the points of interest. It also gives you an R0j-ref, were thetaj denotes junction and ref denotes reference point. This is the thermal resistance between chip and thermistor location, and I believe is in the units you are looking for, at 0.94. edit: I see you found already, that it is ~1.
Actually you are right it is .94,
Somehow I missed it the first time I went through the datasheet

+1
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03-01-2013, 08:51 PM #7
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BShanahan14rulz
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Re: PT54 Help

Sounds like someone's gonna be driving one of these to its limits

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