PEK vs. Gadget Gangster's voltage regulator set-up?

vanmunch

Hello,
I'm diving into my first PCB design and figured that I would use the PEK basic schematic, but then I was looking at how Gaget Gangster has his Propeller USB board and saw that he used 47uF capacitors instead of 1000uF. Nick also had a bunch of smaller capacitors. I was wondering if anyone could explain the reason for each set-up and suggest what would work best for my small, portable, audio player application (it will run off a 9v battery and play short audio clips. Nothing too fancy)? I appreciate any help. Thanks!

Dave

Links:
PEK pg 27
http://www.parallax.com/Portals/0/Downloads/docs/prod/prop/PELabsFunBook-v1.1.pdf

Gadget Gangster's
http://www.parallax.com/Portals/0/Downloads/docs/prod/prop/32208Schematic.pdf

tonyp12

The problem is that most batteries have high output impedance, and can not handle spikes in the current requirement.
So with a battery powered device it's always good to go with a 1000uF cap.

With A/C adapter going with anything from 47uF to 100uF is OK, but bigger will not hurt either.
Smaller caps in parallel like 0.1uF filter out ripples/noise (decoupling)

vanmunch

Hey Tonyp12,

Thanks for the info and help. That makes sense. I think that this helps explain to me what happened when I tried to use the PEK system to reduce to voltage from a 12V 12A lead battery to 9V to 6V and then use the 6V to power the servos of my robot rover/arm, Nuntius (link below). I don't think the servos were able to get enough power from the battery. Would increasing the size of the capacitor or doubling the number of voltage regulators help? Each regulator is rated for 1.5 amps. My fix was to just run the servos from a different 6V battery, but I'd like to eventually run everything off the Pb battery.

If you, or anyone else has time, I do have one more question about the Gadget Gangster regulator set-up. I'm looking at the board and it looks like the smaller value SM capacitor components are ceramic with no polarity. Is it ok to use non polarity capacitors for the smaller values (4.7, 0.1, 0.01)? Thanks again for your help.

Dave

Nuntius:
http://forums.parallax.com/showthread.php?132860-Nuntius-My-Messenger-Robot

tonyp12

Always try to use a battery that is around 1.5-to-4V higher than your Voltage Regulated output needs.
A cap can only help with very short spikes, not extreme power requirements that last 1second etc.

You will need to start looking for mA rating for you servos and electronics and add them up,
and get a battery and voltage reg that can handle that.


It's OK to use no-polarity cap anytime, it's just when they have bigger value you can longer find them (or at least afford them)

vanmunch

Ok, great, thanks for the help. This is very helpful!