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

 

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

 

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.

 

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:

 

thank you guys

 

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 ...