AVR-Chat

--- In AVR-Chat@yahoogroups.com, jay marante <jaythesis@y...> wrote:

> ... the 7805 voltage regulator
> heats up the heat sink too much.

You have the information you need to solve your problem in other 
posts. But, I would like to ask what you mean by "too much". Are you 
worried that the 7805 will be damaged or is the temperature a problem 
for some other reason?

Regulators are typically OK with junction temperatures up to 125 
degrees celsius. A TO-220 package typically has a junction to case 
thermal resistance of three degrees celsius per watt. Let's guess 
that your heat sink has a thermal resistance to ambient of 15 degrees 
celsius per watt and ambient temperature is 30 degrees. A quick bit 
of math, just like solving a voltage divider of two resistors, and we 
get the maximum heat sink temperature of 109 degrees. Thus, the 
regulator will be OK even if the heatsink is hotter than a boiling 
pan of water. Maybe you're worried for nothing! Mind you, if this 
heatsink is somewhere you might touch it, other factors come into 
play, which is exactly what I'm getting at.

Graham.