[GreenKeys] New 60ma current loop driver board design

[COURYHOUSE at aol.com]

Great Info!
I  did have a fear of blowing  item up!
ed#  _www.smecc.org_ (http://www.smecc.org)  
 
 
 
In a message dated 10/29/2016 4:06:49 P.M. US Mountain Standard Time,  
rmowery28146 at earthlink.net writes:

This may  help.  Seems the original usb 1 and 2 could deliver 500 ma.   The
newer connectors have more pins to negotiate how much power to send  out.

http://www.extremetech.com/computing/115251-how-usb-charging-works-or-how-to
-avoid-blowing-up-your-smartphone




>  -----Original Message-----
> From: GreenKeys  [mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of
> Rob  Doyle
> >
> > So how is it then, that "dumb" USB-powered  devices, such as these
> > little USB fans & lamps, can pull a  current from the USB port without
> > sending any sort of  request-to-enable signal? I was always under the
> > impression the  the +5V was available at all times, on the port -
> 500mA
> >  for 2.0, (less) for 1.X and (more) for newer 3.X specs?
> 
> I'm  pretty sure that a computer will only deliver low power (100 mA)
> until  the powered device requests, via the enumeration process, a high
> power  (500 mA) setting. That's what the USB 2.0 spec says.
> 
> I have a  USB desk lamp that definitely does not enumerate. I've always
> assumed  that it draws less than 100 mA. Maybe I'll measure it.
> 
> >  And if the USB port doesn't supply constant power, how does the
> >  USB-powered device make that request without a power source?
> 
>  The USB controller that John used has an internal EEPROM that controls
>  the 'Max Power' parameter. He said "This is reprogrammed to talk 45
>  baud, and to ask for 250mA of power from the USB port. Once the USB
>  port has come up and the other end has agreed to supply 250mA, ENABLE
>  goes high and U2 turns on power." In other words, his USB-powered
>  device does not draw high power until after enumeration.
> 
> >  This is genuinely confusing.
> 
>  

______________________________________________________________
GreenKeys  mailing list
Home:  http://mailman.qth.net/mailman/listinfo/greenkeys
Help:  http://mailman.qth.net/mmfaq.htm
Post:  mailto:GreenKeys at mailman.qth.net

2002-to-present greenkeys archive:  http://mailman.qth.net/pip
ermail/greenkeys/
1998-to-2001 greenkeys archive:  
http://mailman.qth.net/archive/greenkeys/greenkeys.html
Randy Guttery's  2001-to-2009 GreenKeys Search Tool:  
http://comcents.com/tty/greenkeyssearch.html

This list hosted by:  http://www.qsl.net
Please help support this email list:  http://www.qsl.net/donate.html
Message delivered to  couryhouse at aol.com

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/greenkeys/attachments/20161029/1d967c08/attachment.html>