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# 9V DC to 5V DC with LM317

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#### Yoshidk

##### Newbie level 6
Hi all!
Im building a small project with an µC (ATmega16), some ICs (ULN2001A) and some "12V strip LED", so i need both 12V DC for the LEDs and 5V DC for the µC..
So my thought was using a 12VDC supply and "reduce" part of this to 5VDC for the µC

Is the best and most effective way to this with a LM 317?

If i can use this, why does the datasheet say "Vin >= 28V"?

Also i have found a calculator for Vout:

Does these components sound right:
R1 = 240 ohm
R2 = 720 ohm
(Vout = 5V VC)

Thank you
Jeppe

You could also go for a 7805 fixed voltage regulator to get 5V output for your microcontroller. This eliminates the need for the two resistors R1 and R2.

The R1 and R2 values should be bigger since the current through these resistors would be a waste. You could go for a 240k, 720k resistors.

Btw your title says 9V to 5V while the content says 12V to 5V. Both are possible but the power dissipation is different.

You could also go for a 7805 fixed voltage regulator to get 5V output for your microcontroller. This eliminates the need for the two resistors R1 and R2.

The R1 and R2 values should be bigger since the current through these resistors would be a waste. You could go for a 240k, 720k resistors.

Btw your title says 9V to 5V while the content says 12V to 5V. Both are possible but the power dissipation is different.

Oh yea, 7805 seem like a much better solution!
And yea im not 100% sure what LEDs/battery to use, so i messed up the 9 and 12V.. And if i use the 7805, would it matter if i used 9 or 12V?

What capacitors would you suggest? I found:
0,33µF and 0,1µF, does these seem reasonable?
http://www.sminntech.com/techai.html

What total current you need at 5V ?

For uC and rest light parts together with 7-seg and LCD displays you dont need much current. Maybe 78M05 (0,5A in SMD) is enought for that job.

As mentioned before, use at least 10uF (I usually use at least 100uF) before and after regulator, and on end put 100nF, and add one additional 100nF nearest as possible to +/- of uC.

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