[sdiy] AC Adapter - Getting Negative Voltages?

[Derek Holzer]

Hi Ken,

I was looking into all this as well as part of my small form-factor PSU 
plans. Have a look through that thread for some other ideas about small 
power supplies for a briefcase-style modular... The MFOS PSU was 
recommended to me to look at, there's a pretty good explanation of how 
the rectification works there:

http://www.musicfromouterspace.com/analogsynth/WALLWARTSUPPLY/WALLWARTSUPPLY.php

best!
Derek

mcb, inc. wrote:
> On Mon, 27 Oct 2008, Ken Elhardt wrote:
> 
>> Since nobody seems to know of any really small power supplies, as per
>> my previous post, I have question about AC adapters.  How does one get
>> a negative voltage from one?  Is there some kind of negative voltage
>> regulator that works off a positive voltage?  Or do you use the
>> positive voltage as ground, and ground as a negative voltage somehow?
> 
> There are things that do that (charge pump things).  But the
> simpler/traditional way is half-wave rectification.  One side
> becomes ground, the other goes through a diode to the plus
> supply on one half cycle and through a second diode to the
> minus supply on the other.  Halves the frequency which results
> in more ripple, worse surge, etc.

-- 
derek holzer ::: http://www.umatic.nl ::: http://blog.myspace.com/macumbista
---Oblique Strategy # 91:
"Infinitesimal gradations"