LM2596: About measuring junction temperature

Kaji@PAN

Part Number: LM2596

Hello,

I would like to ask you about measuring the junction temperature of the LM2596T-12.

This package is TO-220, but this time I use it without a heatsink.
(question 1)
What is the thermal resistance value (Rθj-c) without a heat sink?
Please let me know if you have any specific numbers.
(Question 2)
I measure using a thermocouple.
What are the precautions when measuring thermocouples?
Is the IC surface a good measurement point? Or is the back of the IC good?
(Question 3)
Please tell me the formula for calculating the junction temperature during this measurement.

Best regards,

over 3 years ago

0 Daniel Li14 over 3 years ago

TI__Mastermind 27040 points

1. without heatsink, it is 50deg C/W

2. IC surface will be good than back of IC

3. When you have a good thermal dissipation like heatsink for TO220, Junction temperature will be very close to Case temperature cause most heat dissipation is flow through heatsink. you can also get some Tj from wenbench simulation.

0 Kaji@PAN over 3 years ago in reply to Daniel Li14

Mastermind 7260 points

Thank you for your reply.
Third question, if I don't use a heatsink, can the formula use the following?

Best regards,

+1 Daniel Li14 over 3 years ago in reply to Kaji@PAN

TI__Mastermind 27040 points

Hi Pan

Even you not use heatsink, most heat still will go from DAP instead of CASE, so I think Tj ~= Tcase. Tj=Tcase+( ψJT*Power)

I don't have number for TO220, but for SOIC8, ψJT is around 9.9deg/W, ψJB=25.4 deg C/W

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LM2596: About measuring junction temperature