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Press the 'S' key on keyboard.
Enter this line into text box .step temp 0 50 10
This will step temp from 0C thru 50C in 10 C steps
To measure the wattage dissipation of a component , place the cursor on the components and press and hold down the ALT key, a thermometer cursor should appear
Read the Watts on the bottom screen screen status text
Hmm, I forgot to ask. After I have write the .temp 100 as a SPICE directive, I can just simply use the thermometer cursor to see the watt losses, right?
I just want to make sure that I understand this correctly.
A resistor will have the same loss.
In the real world we put the power supply in a hot room and see if it survives.
In SPICE we can not have a hot room. We can only force the inside of all parts to be at 25C or 100C or .......
I think y0u are confusing heat loss with a device's power dissipation.
The power dissipation is determined by the power loss in the device and does not vary with ambient temperature.
The temperature of the device increases until the power dissipation to its surroundings equals the internal power dissipation of the device, as determined by the thermal resistance to ambient.
Spice does not determine that temperature rise.
You can determine the rise by measuring the device wattage (dissipation) in Spice, and then calculating the rise from the device's thermal resistance to ambient, which is determined by the device's package, how its mounted on a circuit board, and whether it has a heatsink.
Okay, I'm confused about what you are trying to do.
You cannot learn anything about power dissipation by changing the temperature of the device in simulation.
Power dissipation is a function of the power dissipated in the device by the circuit voltages and currents.
That's what causes the junction temperature to change.
And the only way you can find the actual junction temperature is to know the devices power dissipation and it's thermal resistance to ambient.
Is that clear?
Okay, lets work backwards as you seem intent on doing.
Let's say the junction temperature of a device is 100°C at a room ambient of 25°C, with a junction to ambient thermal resistance of 10°C/W.
That means the device is dissipating (100-25)/10 = 7.5W.
Note you can only make that calculation if you know the device's thermal resistance. and that's not part of the Spice models.