[sdiy] Fw: Distribution board bypass caps?

[Oscar Salas]

I only wanted to consider conductor resistances rather than design with them. The straight solution is to use big conductors yes I agree.


Then, For example for euro-rack power distribution buses, that power is distributed with long traces should be correct to place bypassing capacitors?


----- Original Message -----
From: Harry Bissell <harrybissell at wowway.com>
To: James Coplin <james at ticalun.net>
Cc: Oscar Salas <osaiber at yahoo.es>; Synth DIY List <synth-diy at dropmix.xs4all.nl>
Sent: Wednesday, January 18, 2012 9:04 PM
Subject: Re: [sdiy] Distribution board bypass caps?

I question the wisdom of trying to use conductor resistance as a circuit element. The conductors would need to be REALLY
tiny to have much effect on the inrush current of capacitors. It also guarantees that for any current transient, the voltage
will be poorly regulated.

I'd use really BIG conductors, whatever capacitors you deem necessary... and if the current gets too high consider using a sort
start circuit so the inrush current is not too large. My larger designs use a LOT of decoupling caps, one per chip per supply
voltage (and then maybe 100 chips :^)

I'd say the right place for decoupling is on each individual module...

H^) harry


----- Original Message -----
From: James Coplin <james at ticalun.net>
To: Oscar Salas <osaiber at yahoo.es>, Synth DIY List <synth-diy at dropmix.xs4all.nl>
Sent: Tue, 17 Jan 2012 14:02:44 -0500 (EST)
Subject: Re: [sdiy] Distribution board bypass caps?

All the boards are on their own run back to the supply (a Power-One so a
good one) on 14 gauge stranded.  I have the supply under the desk and the
longest run would probably be 4' - 5'.

James R. Coplin

-----Original Message-----
From: Oscar Salas [mailto:osaiber at yahoo.es]
Sent: Tuesday, January 17, 2012 12:10 PM
To: James Coplin; Synth DIY List
Subject: Re: [sdiy] Distribution board bypass caps?

Yes , good question, I'm also thinking about it these days.

I think that must be considered the resistance of the cable that connects
the power supply to the board, and also the resistance of the traces of
the board, if connectors are placed as a bus.

For example if Distribution Board
is close to the Power Supply and the cables are short and thick, so low
resistance, it will no needed decoupling capacitors at all.

In the other hand if cables are
long and thin, so a considerable resistance, maybe you will need big
filter capacitors in order to avoid any noise, or undesired signal in the
audio range, looping through the modules to the distribution board.

Also must be considered that big
capacitors will increase or create inrush current. However if cables have
considerable resistance, they will limit it.

So I think that the idea is, to more (power supply to distribution board)
cable resistance, more big capacitors.

This is my thought.

More ideas?





----- Original Message -----
From: James Coplin <james at ticalun.net>
To: Synth DIY List <synth-diy at dropmix.xs4all.nl>
Cc:
Sent: Tuesday, January 17, 2012 5:51 PM
Subject: [sdiy] Distribution board bypass caps?

If I have a distroboard for 10 5u modules, what would be the "correct"
size for bypass caps?  I don't know what the exact draw of the modules
will be so I need something to reasonable cover a "typical" case.  The
supply is a 3A supply and there will be 4 distro boards total in the
system although as some modules are double width, I'll never have 40
modules installed.

James R. Coplin
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Harry Bissell & Nora Abdullah 4eva