[sdiy] AC Adapter - Getting Negative Voltages?

[mcb, inc.]

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.

--
Monty Brandenberg