D
Dummy
- Jan 1, 1970
- 0
What's ground loop actually? Ground current exists? Why does it happen
and how to prevent?
and how to prevent?
Sir Charles W. Shults III said:As you know, there are no perfect conductors in the things we build. If you
are wiring a circuit, it is sometimes difficult to get all the ground wires tied
to a single point, and you will occasionally end up with a loop in your ground
system.
In some applications, this will not present a problem. But in other cases,
in particular in audio amplifiers or sensitive sensor and instrumentation
amplifiers, you will have a significant difference from one end of the loop to
the other.
To illustrate how this causes problems, take any complex circuit board and
measure the supply voltage right where the power is connected to the circuit
board. Then, with the ground lead still at the ground connection, read the
power supply voltage at the farthest chip on the board. You may see a half volt
difference or more in some cases.
Now imagine that you have a standard "star" type ground arrangement and
decoupling capacitors on each chip- no problem, ground noise will be pretty much
taken care of. But in a loop you end up with two problems- one is that their
can be a large difference across the loop which may actually drag ground up a
quarter to a half volt in parts of the circuit that otherwise would be
unaffected. The other is that a loop acts as an antenna and can also pick up
switching transients.
For many logic applications, the only real problem you may see is either
"brownout" on some chips or a loss of noise immunity- which can lead to "hair
trigger" or sporadic operation. Faulty clocking or state changes can happen
then.
But for audio applications, the ground loop can be death- unexpected tiny
noises become avalanches of audio garbage, adding pops and clicks, whines, and
hum to the final output.
And one final item- in some cases, a ground loop can actual resonate or
oscillate. You can only imagine what this can do to sensitive components that
want a clean regulated supply for operation.
In summary, avoid the ground loop. It can cause vague, hard to track down
problems in digital systems, and outright terrible performance in audio and
instrumentation. Stick with "star" or single-point ground, and try really hard
to isolate digital ground from analog ground when both are present.
Cheers!
Chip Shults
My robotics, space and CGI web page - http://home.cfl.rr.com/aichip
Marlboro said:keep in mind that the digital return currents are top
killers and must be well isolated from analog section.
Stick with "star" or single-point ground...
isolate digital ground from analog ground...
Chip Shults
transport speed for electrons in Cu
(about 0.67c - 1ft/ns)
Andrew Paule
What's ground loop actually? Ground current exists? Why does it happen
and how to prevent?