Pi filter

[wuchy143]

Hi,

I have been looking at discrete PI filters for my boards and was wondering what people typical do when filtering power rails. Specifically the GND rail. If you look at my attached file you see both +5v and GND as the inputs. I'd like to also filter GND but looking at how I have it set-up C18 is doing absolutely nothing. I've seen people attached the C18 directly to chassis. Is that the best way to deal with this? If not what's a better way? Better filters out there?

Please note: PWR rails only will be delivering a max of 500mA at 5v. There is no high speed on my PCB. There is a PWM controller for a bank of 100 leds intensity. There is a PIC18f45k50 on there doing some basic capacitive sensing. Really nothing too exotic.

Thanks!

 

[ericgibbs]

hi W,
The upper left ground symbol is your chassis or common 0V rail not Earth ground.
E

 

[wuchy143]

hi W,
The upper left ground symbol is your chassis or common 0V rail not Earth ground.
E

oops sorry for not being clear. The GND connection(upside down xmas tree symbol) in the upper left of the schematic is the common Ov rail. Actually C18 is connected to the Ov common rail on both sides of it's terminals. I'm not showing chassis anywhere on this schematic. I'm trying to figure out the best way to shunt energy off of the +5v rail AND the Ov common rail.

 

[wuchy143]

This post never really went anywhere...

What am I missing?

 

[ericgibbs]

Hi,
I dont see C18 connected to both terminals.??

Why do you think you need this level of filtering on the PIC supply.??
E.

 

[wuchy143]

Thank you for the clarification/help. It appears the way you have it is the best approach to filtering in my applications.

I am filtering to this extent due to MIL Standard 461. I have to pass all my electronics to the EMI standard which has been difficult to pass in the past. It has, from what I'm told, very tough conducted and radiated tests.