Am 27.09.2013 08:24, schrieb Markus Gaugusch:
>
> So my question is: How can I improve the power supply on my bus?
>
I feed +8V to my extra power lines and have a small 5V regulator at any
tap.
When powering devices through the bus cable, you have to take care the
ground level isn't lifted too high (higher than 0.7V) on the far end by
the flowing current, as the device in that case may not drop the 1w wire
low enough for the host to notice.
That said, the voltage drop should be *unevenly* distributed between Vcc
and GND, so don't have 2 Vcc wires + 2 GND wires but rather 1 Vcc wire +
3 GND wires. Voltage drop on the Vcc line isn't "seen" by the bus
protocol, on the GND wires it's causing problems.
>
> First question: If my DS2480B is powered by USB port from PC, could there
> be some voltage offset between the "USB ground" and the ground of a more
> powerful external power supply?
>
The USB ground is connected through a small coil with the PC ground.
That is usually irrelevant. When the coil is fried by overcurrent
(usually above 2A), you will notice.
Second, the PC ground is often connected to the mains earth wire. That's
important when your additional power supply has a similar connection, as
there will be a ground loop through the earth wire. It means the onewire
ground is earth, which will allow you to pick up a large amount of noise
through that antenna.
Don't do that! When you use an external power supply, you have to make
sure it's ground is *not* connected to earth.
Kind regards
Jan
------------------------------------------------------------------------------
October Webinars: Code for Performance
Free Intel webinars can help you accelerate application performance.
Explore tips for MPI, OpenMP, advanced profiling, and more. Get the most from
the latest Intel processors and coprocessors. See abstracts and register >
http://pubads.g.doubleclick.net/gampad/clk?id=60133471&iu=/4140/ostg.clktrk
_______________________________________________
Owfs-developers mailing list
Owfs-developers@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/owfs-developers
