SMD project -- 10uf voltage regulator cap -- polarized or non polarized?

Using Arduino General Electronics
1


in your basic voltage regulator schematic like this:
I'm wanting to go all SMD so I'll use a LM1117 regulator.
I picked out a 100uF Aluminum polarized Cap, but what about the 10uF, does it need to be polarized? I picked this out, but it's not polarized...

Does it need to be?

2

You've picked a ceramic capacitor, which is not polarized, and that's OK. It's a good choice, as long as your input voltage is <16V (as that is the rating of your capacitor).

--
The Quick Shield: breakout all 28 pins to quick-connect terminals

3

I recently bought some of these to use with a switching supply, they worked fine, and I thought the price was good:

4

Thanks!

5

Please, do not forget to put a 100 nF ceramic non-polarised cap on the input and the output of the vreg, it's more important than the 100 uF "bulk" capacitor if you want it to behave nicely.

// Per.

6

Zapro:
Please, do not forget to put a 100 nF ceramic non-polarised cap on the input and the output of the vreg, it's more important than the 100 uF "bulk" capacitor if you want it to behave nicely.

// Per.

hi can you explain this more? (or edit the schematic to show?)

do you mean 1 x 100nF cap on the vReg input leg going to the vReg output leg?

7

Look at this:

So alongside your tank caps (10-100 uF) put the 100 nF caps, they should be close to the regulator, maximum 10mm trace length, or they won't do any good.

Actually the drawing is a bit misleading, i would have drawn the 100 nF closer to the regulator to show that these need to be closer that the tank caps.

Your tank caps do not need to be close to the voltage regulator. Say you have a big PCB, and you have the power input and regulator in one end of the PCB, the circuit that needs the power is on the other end of the PCB, then place the tank cap for the regulated voltage alongside your circuit, not the regulator. It then acts like a reservoir of power for your circuit, smoothing the voltage sag you will get on a long track alongside the PCB.

// Per.

// Per.

8

thanks for the schematic!.. it clears up your comment for me.

(also understood about having the 100nF caps close to vReg as possible..... and the 'tank caps' (as you have been referring to them as) can go elsewhere along the power rails/circuit..etc.

:slight_smile:

9

Looking at the LM1117 datasheet, it suggests 10uF tantalum capacitors on both the input and the output, so that's what I would use. Ceramic capacitors would be a suitable substitute, but for 10uF they are likely to be larger than tantalum ones.

10

Ceramic capacitors usally have lower ESR than any kind of electrolitic caps, therefore the are better in most design, including linear voltage regulators.

11

have lower ESR than any kind of electrolitic caps, therefore the are better

Note that the LM1117 datasheet has a specified range for the output cap ESR. Ceramic caps might be too low. (I couldn't find an ESR spec for the panasonic cap mentioned :frowning: )

I think some of these "requirements" are more folklore than necessity in most situations, but I wouldn't be able to say just when they DO become necessity...