LM1117 3.3V Heat Sink Requirements

Hi There!

For one of my ESP8266 project, I need to bring down 12V to 3.3V. My plan is to use LM 1117 for the same. My maximum power draw can be 215 mA, I believe this will equate to 1.8 watt ((12-3.3)*.215 = 1.8705). My question is which chart on the datasheet tell me whether I need heat sink or not for this requirement? From the internet I found that it can operate without heatsink up to 2 watt.. but I would like to know how to determine this from the data sheet. Thanks in advance!

Link to DataSheet: http://www.ti.com/lit/ds/symlink/lm1117.pdf

I'd suggest you just go-ahead and try it. The LM1117 has thermal protection so it will just shut down if overheated. It shouldn't burn-out. If it shuts-down, add a bigger heatsink. ;) Or, change to a switching regulator (which is more expensive because you need an inductor).

Design & calculations can get tricky because as the ambient temperature rises the junction temperature will also rise... So, it might shut down on a hot day, or if it's located where outdoors or near a window where the sun can directly heat it up. ...And, there are usually some unknown thermal resistances... and the calculations can just get complicated.

Without a fan, the "ambient" temperature in your enclosure will rise from the heat put-out by the regulator. (Even with a fan, it will rise to some extent.) Either way, that's almost impossible to calculate.

1.8W definitely should have a heatsink, unless you really want it to run super-hot... TO220 package?

SOT-223 is ~62C above ambient per watt without heatsink. That would make it stinking hot and shut down at 1.8watt. I would say 1.8watt needs at least a square inch of circuit board copper. Can't you use a micro-power buck converter? They run cool, and only use ~70mA from your 12volt supply for 3.3volt/215mA output. https://www.pololu.com/product/2097 https://www.pololu.com/product/2843 Leo..

Thanks All for your responses. I will add a good heat sink

1.8W definitely should have a heatsink, unless you really want it to run super-hot... TO220 package?

Yes, TO220 package.

I agree - 2w into a TO-220 package is going to get hot without a heatsink. It may last for a while, but better design is to keep the components at a much more reasonable temperature.

Consider, for example, the temperature of a 4W incandescent "night light" bulb.