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UA78L: How to measure Tt

Part Number: UA78L

Dear TI team

I would like to know how to measure the temperature at the top of the package while the UA78L12ACPK is in operation.

Our customers are trying to find the junction temperature using the formula below (extracted from the material below).

Among them, our customers are considering using a thermocouple (type t with a wire diameter of 0.2 mm) to measure TT.

I would like you to answer the following questions.
1. It is believed that the thermocouple cools the top of the package during measurement and measures a temperature that is different from the actual temperature.
If you have any other concerns about using thermocouples, please let me know.

2. The above material uses Thermo-gun. When measuring TT, I think it is better to measure it in a non-contact manner like Thermo-gun. Is the recognition correct?



  • Hi,

    Your understanding is correct attaching the thermocouple will result in some error to the measurement since the thermocouple will provide extra conductive cooling through the top of the package. Using a non-contact method like a thermo-gun would be preferred however they will need to make sure the settings are correctly set based on the manufacturer's guidelines and one specific setting to be aware of is the emissivity of the surface setting (plastic IC packages are typically ~0.95).