Power MOSFET thermal analysis

[Surya403]

Hi Team,

We are looking for detailed thermal information for the STD47N10F7AG MOSFET. I am new to power MOSFET thermal analysis and would appreciate your support.

Could you please share the junction-to-ambient thermal resistance (θJA) value or any relevant thermal characterization data required for thermal calculations?

From the datasheet, I could find:

• RθJC (Junction-to-Case) = 2.5 °C/W [st.com]
• RθJ-PCB (Junction-to-PCB) = 50 °C/W (mounted on a 1 in² FR-4, 2 oz copper board) [st.com]

However, I could not locate the θJA specification and would like to use it for thermal analysis.

Thank you for your support.

Thanks & Regards,
Surya

[Johnsmiteo]

Thanks for raising this question. I'm interested in the answer as well. Thermal performance can vary significantly depending on PCB layout, copper area, and airflow, so having a reference θJA value or thermal characterisation guidance from the manufacturer would be very helpful for accurate thermal calculations, especially for those who are new to power MOSFET analysis.

[AScha.3]

Hi,

the   “ Junction-to-PCB = 50 °C/W”  is the θJA here, assuming 1 in² FR-4 board is the “ambient” (→ to air ).

So you can just guess or expect a value of 130 ...30 °/W , depending on copper area, layers in board, etc.

The value cannot be given in datasheet, as it depends 95% on your board/design.

So try to keep losses low and calculate with the help of the AI the cooling “to expect”,

then check /verify on a real test board, or use a heatsink with the needed thermal properties,

to be sure about the cooling you get.

see: 

https://www.heatsinkcalculator.com/blog/how-to-calculate-the-thermal-resistance-of-a-pcb/

 

https://heatsinkcalculator.com/pcb-temperature-calculator.html

 

 

[Surya403]

Hi Team,

Please find attached the calculation sheet comparing the existing MOSFET (NTD5414ANT4G) and the proposed replacement (STD47N10F7A).

Could you please review and verify whether the thermal calculations are valid? In my analysis, I have considered the θJA value as Rth(j-pcb).

I would also like confirmation on the following point:

Since the calculated junction temperature of the STD47N10F7A is below its maximum rated junction temperature of 175°C, can we conclude that the MOSFET is capable of safely handling the calculated power dissipation under the given operating conditions?

Please let me know if any corrections or additional considerations are required.

Thanks & Regards,

Surya