LM317 Caps necessary?

Thread Starter


Joined Apr 21, 2009
Want to use a 3c Lipo to replace the AA batteries on a RC toy (4.5VDC).

All the sample LM317 schemas I see have caps in them.
Are they needed or just there to smooth out the ripple from rectified AC?

(I have the caps in stock, but trying to keep things as simple, small and light as possible)



Joined Mar 14, 2008
The input capacitor (0.1μF) is recommended if the device is very far (more that a few inches) from the supply.
The output capacitor is only for improving the transient response to sudden changes in load current.


Joined May 23, 2013
As #12 has pointed out, if you don't want an oscillator, you need the capacitors. You also need to look up the manufactures spec for the type of capacitor, some only work properly under all conditions with the specified type. If they say use a Tantalum, use one, if they say use a ceramic, then take their advice. After all, they designed and manufacture the thing and as previously stated, they don't add components for fun.
I learned to my cost some time ago that even the same type from different manufacturers sometimes need different external considerations such as capacitor type, recommended max lead lengths etc.