I may have missed some of the earlier posts for this, however based upon wh=
at I
read here, I take it someone wants to create DC power for use in a project.

If you use a full wave bridge and proper filtering capacitors, there is no
reason for it to be "bad" to draw power from the line and convert it to DC.=
  I
have been doing this for many years in machine controls for industrial mach=
ine
tools with no problems.  Now, if you are looking at low voltage DC supply,
always use a transformer to step the AC down first then rectify it.  Using =
the
line voltage rectified and then regulating the voltage with say a Zener Dio=
de is
very dangerous.  For starters more exposure to the higher line voltage, als=
o if
you experience a short in you regulating circuit, you can get the full line
voltage put into your low voltage circuitry, I think we all know the result=
 from
that.

Hope this is of some help.

Randy Abernathy
CNC and Industrial Machinery=20
service, repair, installation and=20
design

4626 Old Stilesboro Rd NW
Acworth, GA 30101
Fax: 770-974-5295
Phone: 678-982-0235
E-mail:=20
randyabernathy@bellsouth.net


-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
Robert Rolf
Sent: Wednesday, May 11, 2011 8:39 PM
To: Microcontroller discussion list - Public.
Subject: Re: [PIC] How to achieve 10 bit PWM resolution at various frequenc=
ies?



Joe Koberg wrote:
> It was my understanding that it's "bad" to draw DC from the line, so I=20
> was wary of drawing half-cycles. (Imagine if your output setting was 50%=
=20
> and you were consuming every other half cycle).

Why would DC draw be bad? Full wave rectifier transformers draw DC on=20
each half of the secondary, so that can't be an issue.

Some simple minded lamp dimmers just use a power diode to cut out half=20
the power line cycles to get 50% dimming.

Some power engineer care to enlighten us?

R


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