Transformerless power supplies are not uncommon.  Microchip has an app
note that sheds some light on the subject:
http://ww1.microchip.com/downloads/en/AppNotes/00954A.pdf

And there've been countless threads here on the subject.

They are allowed by UL and other safety regulations/organizations as
"safe" as long as the user never comes in contact with any part of the
circuit that's not isolated from the AC line.

And yes, it's vastly cheaper than a switched power supply.  The total
cost for the power circuit is likely under $0.50 in small quantities.

-Adam

On 7/17/06, Hector Martin [PIClist] <hector+piclist@marcansoft.com> wrote:
> I just got a board from a dead de-humidifier, which was powered straight
> from 220VAC. What at first looked like a custom DIP18 chip certainly
> seems to be a PIC judging by the pinout. No transformer for power input.
> No 7805. No nothing. The regulation consisted of a big 1uF unpolarised
> cap, some (smallish) inductors, a large resistor, diodes, and a couple
> Zener diodes (which I assume did the "regulation"). Is this
> reliable/safe? Certainly the most simplistic regulation circuit I've
> ever seen (+5V was tied almost straight to Neutral!). Wonder if it's
> cheaper than an off-the-shelf switched 5V supply though.
>
> Any thoughts on this? Is this actually in common use, and if so, is it
> safe or reliable? Were the designers completely crazy doing this? :)
> --
> Hector Martin (hector@marcansoft.com)
> Public Key: http://www.marcansoft.com/hector.asc
>
> --
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