datasheet question

[samy555]

Hi
The following is part of the datasheet of k3296 osfet
**broken link removed**
what the meaning of PT1 and PT2 and why that big difference (1.5 and 40 watt)
thanks

 

[Jony130]

Without heatsink you can dissipate 1.5W ( ambient temperature 25°C) but when you use a ideal heatsink (you keep the metal case temperature at 25°C), now you can dissipate 40W.

RThja = (150'C - 25'C)/1.5W = 84.3 °C/W - thermal resistance from junction to ambient.

RThjc = (150'C - 25'C)/40W = 3.124 °C/W - thermal resistance from junction to case.

 

[samy555]

Without heatsink you can dissipate 1.5W ( ambient temperature 25'C) but when you use a ideal heatsink (you keep the metal case temperature at 25'C), now you can dissipate 40W.

Thank you very much
TA is ambiant temprature, what does Tc mean????

 

[Jony130]

Tc = metal package Case temperature

 

[shortbus=]

Here's the best link I've found on explaining mosfets and heat. http://www.mcmanis.com/chuck/robotics/projects/esc2/FET-power.html