RE: Switchers vs. linear PSU's

My flux capacitor has never let me down.

Bill

-----Original Message-----
From: owner-vectorlist@vectorlist.org
[mailto:owner-vectorlist@vectorlist.org] On Behalf Of Neil Bradley
Sent: Friday, October 09, 2009 6:22 PM
To: vectorlist@vectorlist.org
Subject: Re: VECTOR: Switchers vs. linear PSU's

> Let me guess, the 78xxs and LM's were about 25 years old. We'll see how
> those switchers are in about 20 more years.

The WPC era of Williams pinball machines were 1992 and onward. The top
problems I've seen are:

1) Intermittent regulation (sudden dip in +5 causing game resets).
2) Low regulation. Over time, they start regulating lower an lower.

Sadly, several of those pins had their regulators replaced to fix
resetting problems more than once, so they weren't even close to being 25
years old. Several were less than 5, and that's after beefing up traces
and connectors.

> Also, a poorly designed/engineered (electronic design, COOLING) linear
> PSU will of course be worse than a good designed/engineered switcher.

As you've pointed out, the terms "worse" or "better" are subjective
depending upon the application. I would never use a linear power supply in
an application where brownout conditions aren't tolerable. At the same
time, I wouldn't use a switching power supply in analog audio circuitry
because of switching noise.

> I'm a collector, and for me it's different for you of course. I want to
> keep the games as original as possible and that includes the PSU.

For me, that's not a consideration. Only heat, power consumption, and
reliability, and from those perspectives, from experience in video games
and pinball machines, switchers win hands down.

> However, my experience with PSU's is based on my work in fire alarm
> systems. F.I. we had a failing auxialiry switching PSU. because it was
> overloaded or maybe even shorted, the PSU switched itself off, but
> turned on again, again noticing the short and switching off again etc.
> etc. etc. This happened at a rate of 2 per second. The result that there
> were several parts almost burning. Would have been a blast to see a fire
> alarm START a fire.

I'd argue that is a design flaw or a misapplication. It's a bit much to
take that one example and apply it to all switching supplies. Switching
power supplies do turn off in overcurrent conditions, so why wasn't this
considered? And how would a brownout condition affect the circuit it
powers? Would it be worse or better?

> I do admit that IMHO this is a design error by the manufacturer of that
> PSU, it should have been tested thoroughly for things like this
> happening in the field.

And it's for that very reason that the implementation should be blamed,
and not the concept.

The on/off is a known behavior of switching power supplies when they're
overloaded. Leakage on linear regulators increases over time as they age,
and is also a known behavior of linear supplies. It's all about using the
right supply in the right application. Pick your poison. ;-)

-->Neil

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C. Neil Bradley - EVERYBODY KERNEL PANIC!
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Received on Fri Oct 9 19:56:02 2009