# LM317 power and heat

#### NOISEBOB

Joined Jul 7, 2019
13
Hello

I need to power a bunch of circuits that ask for 3v and 4.5v and I'm thinking to built a simple circuit using two LM317's and powering it with a 9v power supply..

Would heat be an issue? Do I need heat sinks?

Is there a cleverer way of powering down from 9v to 3v and 4.5v?

Everything is DC BTW..

#### ericgibbs

Joined Jan 29, 2010
10,752
hi,
What is the current load for 3V and 4.5V.?
E

#### NOISEBOB

Joined Jul 7, 2019
13
I'm not sure.. very low I assume.
The circuits I need to power are from kids toys.

#### ericgibbs

Joined Jan 29, 2010
10,752
hi Bob,
If you keep the dissipation in the LM317 below say 2W then it should be OK.
So 9Vdc in and 3Vdc out thats a 6v drop across the LM317,,, so Watts/Volts = Current.... 2W/6V = 0.33A max

For the other 9V - 4.5V drop thats 2W/4.5V = 0.44Amps max

OK.?
E

#### NOISEBOB

Joined Jul 7, 2019
13
Sounds completely reasonable..

Ta!

Joined Feb 20, 2016
3,602
If you find the regs do overheat, try these..

Ebay specials!
Some versions have trim pots to adjust them, some are fixed, and the best have solder pads on the back to select a range of fixed volts, as well as variable.

#### DickCappels

Joined Aug 21, 2008
6,580
When using it if the heatsink tab gets hot enough to boil spit (over 100 degrees C) you should attach a heatsink.

#### cmartinez

Joined Jan 17, 2007
7,080
When using it if the heatsink tab gets hot enough to boil spit (over 100 degrees C) you should attach a heatsink.
Ughh... of all the fluids you could've suggested ...

I normally use a drop of soaped water...

#### DickCappels

Joined Aug 21, 2008
6,580
Just thinking back to my youth -that's how we did it back in the neighborhood.