# How long will resistor last at 104 degC?

1. ## How long will resistor last at 104 degC?

Hi,
We are using your ROX3SJ39K resistor in our new 60W offline Flyback SMPS LED driver.
The product will be meant to operate for 8 hours per night, every day of the year.
We measured a temperature of 104 degrees Centigrade on the surface of the resistor body. The resistor is dissipating 0.5W. The ambient temperature inside the power supply enclosure is 50 degrees C.
Considering this operating temperature, for how many years do you believe that this resistor will last?

ROX3SJ39K datasheet
https://www.te.com/commerce/Document...ocLang=English

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2. ## Re: How long will resistor last at 104 degC?

I believe it will last 8.33 years. Unfortunately, this is not a question of belief; it's a question of engineering. How are you even defining "last"? How long it stays within tolerance? How long before it opens? This is the same ambiguous question you asked about a MOSFET. Contact the manufacturer (and don't use that same excuse 'they won't talk you because you're a small company').

You could also look at this: https://www.sqconline.com/resistor-m...rev-f-notice-2

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3. ## Re: How long will resistor last at 104 degC?

You said Power dissipated in resister is 0.5W, ambient is 50C.
from datasheet, this resister is rated to 3W , actual power is 17% of total power it can withstand. from graphs max temperature rise for ~25% rated power is 50C. So,temperature rise will be ~ 100C which OK.
To know life time of resister with these conditions, there are formulas to find out failure rate of these resisters or you can ask Manufacturer also.
http://rohmfs.rohm.com/en/products/d...ilure_rate.pdf

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4. ## Re: How long will resistor last at 104 degC?

The resistor is dissipating 0.5W.
The resistor is rated for 3W at 70C. You need to make sure that the solder does not melt off!!

5. ## Re: How long will resistor last at 104 degC?

Originally Posted by c_mitra
The resistor is rated for 3W at 70C. You need to make sure that the solder does not melt off!!
If your solder melts at 104 degrees, you need better solder.

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