datasheet question

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

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.

Jony130 said:

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.

Click to expand...

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

Tc = metal package Case temperature

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