[sdiy] DC-DC Converters

[Czech Martin]

Like allways, a general statement like "switching PSU are bad"
is nonsense. "Be carefull witch switcher noise" is better.

It is really a EMI problem.

It depends on time. Through the years switchers have improved.
There are new modulation schemes that try to flatten the spectrum.

It depends on radiation. A good metal case arround the switcher
can eleminate this, but a heat problem remains.
Many units are open frame, so radiation can spread out.

It depends on output line noise, this can not really be eliminated.
There is the triangular or trapezoid up and down of the switcher
principle, and higher frequency dirt from parasitic oscillations,
spikes etc, and maybe some high frequency dirt from the mains line
speakthrough (digital data communication on mains lines is a
super jamming transmitter, but regulation authorities in Germany
refuse to act (prohibit) because of the $ involved, if you or me
would radiate so much EMI, we would get jailed instantly).
A good filter can eliminate most of that. But that is not so easy to do.
Example: a bypass cap will turn into a series resonant circuit at some
specific frequency. The bypass cap will not only stop working, but it can
enhance noise if this frequency matches to something in the PSU/wiring.

And then comes source susceptibility. Narrow band circuits like LC
oscillators will be ok with noise, if it is out of band.
But if you hit a spectral noise line, the circuit will probably stop
working. Low frequency music applications have a wider band, but most
of the noise will be outside. Unfortunately the S/N requirement is quite
high. And out of band noise can be mixed down with nonlinearities
or modulators, like ring modulators or ADC. In this case the switcher
noise can be very anoying.

So switching or non switching supply is a complex question.
With a linear supply you have cost, weight and heat.
But it will allways work.

A switcher is perhaps cheaper, can run with a lot of mains voltages,
has less weight and heat. But it can turn out that the investment you made
is lost, because your application won't like it and you can not fix
it, but the switcher is still on spec, so no chance to bring it back
to the vendor.

m.c.



> -----Original Message-----
> From: owner-synth-diy at dropmix.xs4all.nl
> [mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of Shokwave
> Sent: Mittwoch, 24. März 2004 04:00
> To: WeAreAs1 at aol.com; synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] DC-DC Converters
> 
> 
> 
> ----- Original Message ----- 
> From: <WeAreAs1 at aol.com>
> 
> > Indeed, there is no reason to dismiss them out of hand.  Many of our
> favorite
> > music-making machines have switching power supplies, and 
> you'd be very
> > hard-pressed to ever hear that the power supply is causing audible
> artifacts, or
> > tuning/stability problems with VCO's.
> 
> Indeed, I've been wondering about this. As a new ham radio operator, I
> recently purchased an all-band, all-mode rig and needed a PS 
> for it. Imagine
> my surprise when I noticed that many, many companies sold 
> switching supplies
> for use with HF/VHF/UHF radios! I was floored; the SDIY motto 
> has always
> been "linear please". Anyway, a couple of local EE/ham types 
> told me to get
> a linear, as they were quieter, but obviously many people 
> feel that their
> extremely sensitive radio VCO's work great from switching 
> supplies. They ARE
> more efficient, and tend to be much smaller/lighter.
> 
> My SDIY prejudices made me buy a linear PS in the end, of course.
> 
> -Darren
> 
>