mosfet data sheet doesnt say about junction to ambient

Papabravo

Joined Feb 24, 2006
13,721
hello me again . im trying to understand how hot osfet will get without heatsink. i leared how to calculate that but data sheet for this mosfet doesnt say anything about junction to ambient temp. how can i learn this

https://pdf.direnc.net/upload/utm2054g-ae3-r-5a-20v-n-kanal-mosfet-sot23-datasheet.pdf
You have a power dissipation limit for this device of 1.25 Watts. There is also information on the heat dissipation of standard packages. This package is not amenable to heat sinking so I would go with the power limit and trust that the junction temperature will be less than 150 °C.

http://www.ti.com/lit/an/slva937/slva937.pdf
 

ronsimpson

Joined Oct 7, 2019
679
Many data sheets show typical pads for PCB. (or there is a sheet for package types) The 1.47 or 1.25 watts is with the silicon at 150C and the air at 25C. It is possible to make the PCB so it pulls more heat out.
Do not run the transistor at 150C silicon temperature.
 

dl324

Joined Mar 30, 2015
10,737
i leared how to calculate that but data sheet for this mosfet doesnt say anything about junction to ambient temp. how can i learn this
It seems a number of manufacturers are clueless when it comes to providing adequate information in datasheets.

I'd contact the manufacturer.

For comparison:
BSS123 gives junction to ambient of 350C/W with minimum pad sizes.

AO3400 gives 125C/W under these conditions:
clipimage.jpg
 

sparky 1

Joined Nov 3, 2018
182
The excellent RDs(on) means it is excellent. so warm it and see if Vgs threshold lowers from specs max and minimum at 250uA @20V temperature effect on BVdss ...
 
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