# Ground in DC circuits.

Discussion in 'Electronic Basics' started by [email protected], Jul 26, 2005.

1. ### Guest

Hi!

I have some theoretical knowledge of electronic circuits, but when it
comes to practical, real circuit, there are some issues. The biggest
problem is grounding. I read several articles about loops, but it is
not enough.

E.g.
http://chaokhun.kmitl.ac.th/~kswichit/dcsupply/circuit.gif

0 V and GND are at the same node. (?) Does it mean that I have to
connect it to something (to what?) or does this act as ground.

2. ### Tom BiasiGuest

Hi,
Sometime the symbol for common is taken to mean ground. A ground usually
references the earth somewhere. The schematic you linked uses the symbol to
mean common point. 0V and common are the same in this circuit. You do not
need to connect it to anything.
Very often common will also be grounded.
The terms are used interchangeably sometimes but shouldn't be.
Regards,
Tom

3. ### Guest

Thanks for reply. However I am still curious how to introduce ground to
a circuit. Connect it to metal chasis? Will it play a role of ground?
What in case of plastic case?

To summarize: How to make ground ? But in practical terms (examples
would be nice).

4. ### NogGuest

You can have an isolated ground. Not really a ground, just a complete
circuit.As long as you have current flow in your circuit you don't need to
connect it to earth ground. Sometimes called a floating ground.

5. ### Guest

However, audio circuits are quite sensitive to this, isn't this true?

6. ### Tom BiasiGuest

It is common practice to shield wires carrying audio frequencies and ground
the shield to a common point that will not be above the reference potential.
Usually an earth ground is used by using the ground connection on the power
plug.
Tom

7. ### John PopelishGuest

DC or AC, it makes little difference. The concept of ground serves
many purposes in circuits.

In power circuits, where dangerous voltages are involved, ground is a
safety concern. If a person connects to a dangerous voltage (with
respect to Earth and also connects to Earth, he will complete a
circuit and get a shock. Surrounding the dangerous voltages with a
conductive container that is also connected to Earth will prevent such
an accident. The conductor that connects the container to Earth is
called a safety ground.

In signal circuits, there is often a need for many different parts of
the circuit to agree on a reference voltage that represents zero
signal. This is really a common but is often referred to as ground,
and is sometimes actually connected to Earth, usually through the
safety ground conductor in the power cord. But as far as the signal
circuits are concerned, it makes little difference whether this mode
is actually connected to Earth or not, as long as all parts of the
circuit agree on using this same node as a zero volt reference.
Problems occur if only parts of the circuit use this node and other
parts use their safety ground as a reference.

A third use of ground is as shielding, Signal circuits not only
respond to currents and voltages from internal parts, but also to
capacitive currents caused by unintended electric fields from external
sources of changing voltage and unintended voltages from external
sources of changing magnetic fields. Enclosing the entire system
inside a conductive container (a Faraday shield) that is also
connected to the system zero signal reference node will protect the
system from electric fields. If the shield is conductive enough, it
also offers some protection from penetration of changing magnetic
fields. But for extended parts of the system, (cables) the best
solution is often to also have cancellation of voltages generated by
magnetic fields take place. The magnetic field will tend to generate
the same voltage in each conductor passing through it, so you arrange
the circuit so you subtract the voltage from on conductor from the
voltage from a second conductor, thus canceling the induced voltage
but leaving the desired signal.

8. ### Peter BennettGuest

The term "ground" is much misused in electricity and electronics.

In some cases (AC power wiring and some radio antenna systems) it
really does mean "a connection to the earth".

However, in most cases, particularly with portable equipment, "ground"
just means "the point in the circuit that the designer decided to call
"zero volts". If the equipment is in a metal case, the case will
usually be connected to the circuit ground, as will the shields on any
connectors.

10. ### Kitchen ManGuest

Restricting my answer to the circuit in question: if you have a metal
box, you might connect the 0V point to the box. If you have a plastic
box, it does not matter. It is many times difficult to tell in a
circuit design whether the circuit zero volt return line is meant to
be run to chassis, but in this circuit, it can be safe to assume that
the return point may be a chassis. The one thing you do *not* want to
do is tie that point to the AC input. Transformers isolate circuits,
and you must always be careful to maintain that isolation when
designing or testing.

Just for the record, there are *a lot* of so-called professionals in
the field who don't understand grounding. Even among those who may be
considered versed, there are often strong disagreements about proper
design. You are doing well to pursue the subject.

11. ### Kitchen ManGuest

Things get really fun when using positive-ground power systems, e.g.
the -48V for radios and audio equipment systems.

12. ### Tom MacIntyreGuest

My dad was a truckdriver, and didn't use the same truck all of the
time. One time, using a White (I think), his CB hit ground, and was
hurt. His friend, into electronics, repaired it and installed some
blocking diodes to prevent future mishaps. That was my first
introduction to the diode.

Tom