7805 Thermal Runaway?

Mario · Post by **Mario** » Tue Aug 19, 2008 9:28 pm

Is this possible? I ran my NES from a 7805 at 10v for about ten minutes with a small heatsink, and it got so hot it nearly burned my finger! Is this normal? If not, would some thermal paste help?

Aguiluz · Post by **Aguiluz** » Tue Aug 19, 2008 9:55 pm

Grab a bigger heatsink.

I have a 7805 running a PS2. The 7805 craps up because it was so hot, even on my biggest heatsink.

Jongamer · Post by **Jongamer** » Tue Aug 19, 2008 9:58 pm

It should be fine, 7805s are hard to kill with just heat, as long as your not pushing its limits or getting anywhere near it, which is 30v input, I think you should be fine

Hell I think I ran MY NES from a 15V power supply with no problems at all.

Valium · Post by **Valium** » Tue Aug 19, 2008 10:00 pm

Easiest solution is to just stop touching it

Jongamer · Post by **Jongamer** » Tue Aug 19, 2008 10:04 pm

Valium wrote:Easiest solution is to just stop touching it

Yeah that would be a wise decision.

Sharp Sapphire · Post by **Sharp Sapphire** » Tue Aug 19, 2008 10:30 pm

Valium wrote:Easiest solution is to just stop touching it

Its so hard to resist! You don't know if its gonna burn you or not... can't resist the temptation.

kasar · Post by **kasar** » Wed Aug 20, 2008 5:31 am

Valium wrote:Easiest solution is to just stop touching it

lol

do 7812Â´s have similar heating problems? I supose it will, But I havenÂ´t mine yet for make the finger test

timmeh87 · Post by **timmeh87** » Wed Aug 20, 2008 11:00 am

The amount of heat can be directly calculated.

(Input voltage - Output voltage ) * current = heat (watts)

No, you cant just let it get hot, it says so right in the datasheet. You need an appropriate heatsink. Generally these things have circuits in them that will shut things down if it gets too hot. If you cant hold your finger on it for more than half a second, then its probably too hot.

Post by **Skyone** » Wed Aug 20, 2008 3:42 pm

God this thread is ridiculous.

Either get a new regulator rated for higher power, get a bigger heatsink (I don't really suggest this, it'd be ignoring the problem in a way), or enjoy a dead 7805.

Dr. KillGood · Post by **Dr. KillGood** » Wed Aug 20, 2008 3:47 pm

Put it in a bucket of corn oil or some liquid that wont fry electronics!

timmeh87 · Post by **timmeh87** » Wed Aug 20, 2008 8:49 pm

I dont think you can really get one rated for "higher power", you are physically limited by the size and shape of that little package they are in.

Heat sinking your 78xx is often necessary, it says so right in the datasheet.

Jongamer · Post by **Jongamer** » Wed Aug 20, 2008 9:25 pm

timmeh87 wrote:I dont think you can really get one rated for "higher power", you are physically limited by the size and shape of that little package they are in.

Heat sinking your 78xx is often necessary, it says so right in the datasheet.

Well on my 7808, I run it with no heat sink at all from 10v, and is tucked away inside the Genesis wall wart, so nearly no air is cooling it, Guess what, it has been running 24/7 for a good 3-4 months powering my Linksys switch (Yeah I lost the power cable to it, and no power supply I could find would fit it, I so I just used a Spare 7808 and Genesis power supply.

Valium · Post by **Valium** » Wed Aug 20, 2008 9:36 pm

Jongamer wrote:
timmeh87 wrote:I dont think you can really get one rated for "higher power", you are physically limited by the size and shape of that little package they are in.

Heat sinking your 78xx is often necessary, it says so right in the datasheet.
Well on my 7808, I run it with no heat sink at all from 10v, and is tucked away inside the Genesis wall wart, so nearly no air is cooling it, Guess what, it has been running 24/7 for a good 3-4 months powering my Linksys switch (Yeah I lost the power cable to it, and no power supply I could find would fit it, I so I just used a Spare 7808 and Genesis power supply.

7808 =/= 7805

timmeh87 · Post by **timmeh87** » Thu Aug 21, 2008 10:29 am

Yeah this thread IS pretty ridiculous.

Sometimes regulators get hot. If it gets too hot it needs a heatsink. If it dosent then thats ok too.

Mario · Post by **Mario** » Thu Aug 21, 2008 4:22 pm

This thread IS ridiculous.

I'm using the one that was in the NES's old RF box. And I'll get a bigger heatsink for it. That should be fine, right?