[sdiy] Power supply question

[Magnus Danielson]

From: mikael at mikmo.dk
Subject: [sdiy] Power supply question
Date: Sun,  2 May 2004 13:44:02 +0200
Message-ID: <1083498242.4094df020a5cd at 212.97.132.41>

> I just started to build a few modules. The first thing i am going to finish
> (soon) is a regulated 1A +/- 15V power supply. I am going to put this PS in the
> back of some kind of rack i am going to build for my first modular attempt, but
> should the PS be shielded in a metal enclosure to minimize noise, or is a
> plastic enclosure (for safety) enough ?

A metal casing is good also for safety. Anyway, if it all sits inside the same
box there is benefits in not have a case around the PSU, since the self-
convection allows it to cool off better and thus have a longer lifetime.

> The PCB design i used doesen't have much room for heat sinks, so i was
> wondering if i could take the regulators "of board", mount them on suitable
> heatsinks, and just run wires back to the PCB, or would that introduce noise
> or other problems ?

If you use linear regulators will a shorter run of wires not be a problem and
possibly the best solution. Otherwise you should put the regulators such that
they easilly can sit on both the board and the heatsink.

In the long run you don't want the heatsinks-transistor-PCB to carry mechanical
stress, regardless of how you do it. Mechanical stress and heat makes the
solder more prone to create tunnels around the pin and intermitent contact.
Also, some flexing must be possibel so that vibration and mechanical stress due
to temperature-changes in materials does not create any excess mechanical
stress in the solderjoints.

It is an ugly site when you find one of these flaws, beleive me!

Cheers,
Magnus