Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: gary_ramsgate on August 28, 2009, 05:39:41 AM

Title: smoothing Capacitor
Post by: gary_ramsgate on August 28, 2009, 05:39:41 AM
(http://www.garyandrowena.plus.com/images/5vpsu.jpg)

I'm building a 5v PSU to provide a supply for various low current circuits on my robot.
The input voltage will be approx 12v from a lead acid battery.
This battery is also supplying my motherboard via a PICO 120W ATX DC/DC converter.

I've got a smoothing capacitor (C2) on the input to the Reg.  I'm not sure if this is readlly required as a battery is really a large capacitor.
Does anyone think I need another capacitor on the output of the Reg?

Any thoughts would be appreciated.




Title: Re: smoothing Capacitor
Post by: Joker94 on August 28, 2009, 05:59:54 AM
I have a 100uf infront of my regulator, the $50 robot has a capacitor infront of the regulator. ;D

They are not entirley neccessary but  they are good to protect components from noise and keep the circuit powered in sudden power drains.

so i think they are handy and i would keep it.
Title: Re: smoothing Capacitor
Post by: Soeren on August 28, 2009, 08:54:21 AM
Hi,

I've got a smoothing capacitor (C2) on the input to the Reg.  I'm not sure if this is readlly required as a battery is really a large capacitor.
Does anyone think I need another capacitor on the output of the Reg?
If the battery is fairly close to the regulator (say less than 4"/10cm) you should be able to:
Loose C2 altogether.
Move C1 as close to the pins of the regulator as practically possible - 100nF to 220nF is a good range, but the 330nF will do.
C3 should be around 22F (10F will do if you get a wet tantalum) and preferably a low ESR cap if possible (or move up to 33F or 47F). This should be as close to the regulators pins as well.
The major idea of placing these two caps is to make sure the regulator doesn't oscillate (since that's a bad thing).

Make R1 around 330 Ohm or larger, it's just an indicator (no reason for a blue/white or whatever you went for, when a plain old green LED will be so much more intuitive to read).