PSU design?

[Arthur Harrison]

-----Original Message-----
From: Paul Eccles <pae at ar.com.au>
To: synth diy <synth-diy at mailhost.bpa.nl>
Date: Saturday, December 19, 1998 3:42 PM
Subject: Re: PSU design?


>Tony wrote:

>>Don't use large ground conductors in any psu. Use carefully thought out
>>traces to give a star point grounding system. The amount of Guitar amps
>>that use wodges of copper for the ground supply, and they hum like
>>terrible.

>and Haible wrote:

>>One typical error is to make very broad GND connections
>>and connect everything just anywhere. The currents must
>>be *forced* into a certain path, or they will find the path with
>>least resistance, not least ripple.

Paul Eccles wrote:

>What is the theory behind this? I've always been quite enamoured with huge
>GND tracks; in power supplies and in just about every other circuit. It was
>my thinking that the broader the track, the lower the impedance and
>therefore the lower the hum. What am I not considering here?

AH writes:

In a majority of cases, the use of wide printed circuit tracks is NOT a
detriment to circuit performance.  The fact is that _every_ circuit node
needs to be considered on its own merits.

Haible is correct; the arbitrary connection of multiple currents to a single
return path will usually cause undesirable "cross-talk."
The use of a large conductor will mitigate, but not entirely eliminate,
this condition.

Hence, "star" wiring, advocated by Tony, in which each return current is
brought to a central node called "ground," is a good practice in precision
analog design. However, star topologies do not preclude the use of wide
tracks, which will, in fact, keep voltage drops to a minimum.

In short, (bad pun!) neither wide conductors nor star wiring preclude each
other.  The calculated combination of both techniques is the best approach.

>From a manufacturing perspective, large-width printed conductors are often
more reliable than very narrow traces, as a hedge against tiny "hairline"
cracks.  On the other hand, if solder masking is not employed (rare, these
days)
the solder consumption will increase proportionally with land area.

Unfortunately, from a service perspective, it is quite difficult to remove
an IC
lead from a multiple-layer board that includes a wide track or ground plane!

-Art