Star Ground

[KansaiRobot]

Hello.

I would like to ask what is exactly a "star ground"?? I mean I am understanding it is something like joining all grounds of a circuit at one point and then connecting this point to the ground of the power. Am I getting this right?

And what for is this? I am understanding that this is in case we have two voltage powers (say 5V and 24V) so as not to interfere with each other.

Take a look at https://www.semicon.sanken-ele.co.jp/sk_content/sla7081mpr_ds_en.pdf
fig 12. There we have a star ground.

and then on page 11 it says

Be cautious about noise on the VDD line. When the noise on VDD line exceeds 0.5V device malfunction may be caused. To avoid this, special attention should be paid to the layout of the ground circuits. The separation of the VDD ground and the VBB ground from the product GND pin is effective in reducing the noise

What?

I am guessing the quote above simply means "Put the SLA7080M ground pin between VDD ground and VBB ground" am I wrong??

 

[Mikebits]

ETO member Spec uses this method quite a bit so I am sure he will chime in on this one. This is a old technique still used by many designers. Less used in high speed digital design (according to Howard Johnson author of High Speed Digital Design), but fairly common in your application.
Despite the title A Handbook of Black Magic, HJ attempts to dispel this myth as it only seems so when one lacks certain fundamentals.

 

[MaxHeadRoom78]

The star ground connection is also often connected to the Service Earth Ground.
In machinery containing electronics there is also Uni-potential bonding, where all metalic parts of the machine are bonded to the star point also.
Max.

 

[KeepItSimpleStupid]

I didn't read the data sheet fully, but what you have is a high current system and a low current system. The high current system is "less tolerant" of the voltage drops.

So, what we can do is create different ground busses in our system depending on like characterisics.

A. A digital bus could have lots of switching noise on it
B. An analog bus needs to be clean. i.e. reference voltages.
C. Motors with high current and pulses.
D. Chassis
E. Earth

So, you separate all of these and connect them at one point. You can also "isolate/filter" them a bit, but I won't talk about that,

In a home, there is one point where ground an neutral meet. It does mess up the fact that when say 10 outlets are paralleled, the grounds daisy chain. Our ground is both protective and a reference. If for some reason lightning hit the last outlet in the string, the ground potentials would be different for every outlet. Not good.

In commercial environments there are orange outlets which have an "isolated ground". These have the ground all the way back to the panel. Many business are wired with BX cable. Where I worked, we had a few systems that needed the isolated ground.

Hospitals and radio transmitters are somewhat special.

So, ideally in the home every outlet should have a home run to the service panel, but that's not gonna happen.

The important part is to have only one ground and no loops.
In some lab systems, you can use pseudo-differential analog inputs and current outputs so that the ground don't interact.
The "voltage input" is provided by a current through a resistor.

In a home-made instrument that I/we attempted to modify to make computer controllable, I goofed, In a normal system, there were 3 power supplies, but it supplied say 6 devices. The setpoint to the individual devices was relevent to the device's ground, not the power supply ground. Big oops not to take that into account. Pseudo differential would take care of reading, but not the setpoint.

 

[ericgibbs]

hi K,
Look at this PDF, mainly Section 3.22 onwards.
E

 

[chemelec]

A "Star Ground" or "Common Point Ground", Eliminates Tiny Voltage Drops that can happen between Various Ground Points.