MadSci Network: Physics

Re: Heat Dissipation on electrical components ?

Date: Thu Feb 16 10:03:32 2006
Posted By: Barry Kamrass, Consulting Engineer
Area of science: Physics
ID: 1140081431.Ph

Another good question, Dilan!

The constant K generally applies for a digital circuit, such as a 
microprocessor.  It is a function of the exact transistor size and how 
the wafer was processed.  But the power dissipation of a uP also depends 
on the state of its input and output lines, and so the constant K is 
rarely defined in a manufacturer's data sheet.  If a manufacturer were to 
do so he would possibly be giving away his own trade secret information.  
Also, please remember that the formula is just a rough rule of thumb.  
And for analog integrated circuits the formula does not apply.

While I don't know of any further information to give you, you can almost 
certainly measure the constant K for a given circuit.  Take, for example, 
a simple CMOS chip (such as a NAND gate) and set the experimental rig up 
to measure the power drawn by the chip.  Then drive one of the inputs 
with a variable frequency source while measuring the chip power.  As you 
increase the frequency, the power drawn will go up.  Plot power vs. 
frequency and the slope of the line will give you K (for that chip only).

I hope this helps! 

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