[sdiy] Todays weekly Elektor email...

[Harry Bissell]

No. Load regulation means that the nominal value of DC stays within 5% from no-load
to full-load.  Now, how much does your load actually change (probably not much unless
you are strobing LEDs on and off...  Noise is another thing, that would be an AC signal
riding the DC voltage.

Good filtering can probably quelch the switcher noise, imho. Unless you're an audiophile :^)

H^) harry


----- Original Message -----
From: Noah Vawter <nvawter at media.mit.edu>
To: synthdiy diy <synth-diy at dropmix.xs4all.nl>
Sent: Fri, 13 May 2011 15:28:45 -0400 (EDT)
Subject: Re: [sdiy] Todays weekly Elektor email...


On May 13, 2011, at 2:57 PM, Tom Arnold wrote:
> http://www.elektor.com/news/k78xx-switch-mode-lm78xx.1806960.lynkx
>
> I've seen these parts before, not this one in particular but in  
> general.
> Has anyone used them for synth work?  If they are quiet enough they  
> would be
> a great addition for supply +5 on modules to get rid of those little  
> 7805
> spaceheaters I normally use...

I would take their "up to 97% efficiency" with a huge grain of salt.   
 From what I have seen typical maximum efficiencies for small switchers
are less than 90%.

Also, the efficiency will vary considerably, e.g. 50%-90% depending  
upon the voltage and current you're running it at,
relative to input voltage.  It goes down with larger input voltages,  
and up with larger output currents.  Finally, the maximum
efficiency will be obtained through careful component selection.  In a  
system like their resin-covering, you can't do that anymore.

I definitely agree it's time to upgrade from the 7805 era.

Noise for this device (Load regulation) says less than 5%.  I take  
that to mean @5V:
output is from 4.75V- 5.25V.  So, noise is 0.5V.  That is  
approximately 1/10th the output....   20 * log10(0.5/5) or about
-46 dB of noise.  For analog audio work that is out of the question,  
no?   That seems very, very bad.....
....Am I doing this right?

FWIW, I've been using a chip called LM2574 for a few years now for  
digital supplies.  It requires minimum of components and comes in DIP.
It's also very tolerant of layout.

I'm thinking... if waste heat is the problem (I assume you're turning  
~18V into 5V?) , perhaps you could switch regulate down to
the drop out of your 7805, e.g. 7.0V, then use a 7805 linear in series  
with that.  That way the 7805 cleans up the noisy switched output
without wasting huge amounts dissipating higher voltages.  Opinions?

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-- 
Harry Bissell & Nora Abdullah 4eva