Designing a 5V regulator using smt parts.

Using Arduino General Electronics
1

Hi...

I am revising my designs and I looking at making them more compact. So I am venturing into the world of surface mounted components.

My question is about the capacitors to use with a 5V regulator.

Here are the items I am looking at using:

  • 5v Regulatorhttp://www.digikey.co.nz/product-detail/en/L78M05CDT-TR/497-1203-1-ND/586203
  • 0.33uF Caphttp://www.digikey.co.nz/product-detail/en/CL21B334KBFNNNE/1276-1123-1-ND/3889209
  • 0.1uF Caphttp://www.digikey.co.nz/product-detail/en/CL21F104ZBCNNNC/1276-1007-1-ND/3889093

Can I use the 0805 caps or are there a reason that the little "Can"http://www.digikey.co.nz/product-detail/en/EEE-1HA0R1SR/PCE3913TR-ND/766080 like capacitors are used?

I also notice that the 0.1uf had a crazy amount of tolerance... -20%, +80% (My feeling is that I should look for another option,right?)

Any input will be appreciated. Thanks. :wink:

2

I cant think of a reason to use a 0.1uf electrolytic cap if it were 1uf price would start to factor in, but no use a ceramic

and capacitor tolerences typically suck, you have a +- 10% X7R for the 0.33 so look around those lines if you want to keep everything about the same, course you can loosen up a little bit and drop the X7R rating to drop the price as well

3

Protoneer:
Can I use the 0805 caps or are there a reason that the little "Can" like capacitors are used?

I use ceramic 0805s for 0.1µF, 1µF, and even 10µF. Usually the "can" types are electrolytic, 10µF or larger. That seems odd to have a 0.1µF cap in a can.

I also notice that the 0.1uf had a crazy amount of tolerance... -20%, +80% (My feeling is that I should look for another option,right?)

Given the usual role of a 0.1µF cap as a bypass capacitor, there's nothing wrong with that tolerance. I buy these by the hundred. I usually look for the X5R or X7R temperature coefficient. I'd say that one with the Y5V coefficient isn't desirable.

4

Protoneer:
I also notice that the 0.1uf had a crazy amount of tolerance... -20%, +80% (My feeling is that I should look for another option,right?)

The temperature coefficient for that ceramic is Y5V, which is a class-3 dielectric. It has a very significant voltage and temperature coefficient. You should avoid Y5V and Z5U in almost all cases. For most hobby projects they might be fine, since they work best at room temperature.

5

Good thing you mentioned that as the unit will be used in a growing room for mushroom. The power supply is for a remote MCU(ATMega88) that communicates via rs485.
Temp : -5/50C
Humidity : 50/100%

6

Depending on the input voltage and current used you should pay careful attention to heatsinking the regulator, usually with via-stitched ground planes on both sides but you can also get special SMD heatsinks as well.

Rob

7

Graynomad:
Depending on the input voltage and current used you should pay careful attention to heatsinking the regulator, usually with via-stitched ground planes on both sides but you can also get special SMD heatsinks as well.

Rob

Thanks for the advice... I will definitely add it to my design.