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power ground and signal ground

annapurna

Feb 3, 2017
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can we connect power ground and micro controller ground?
what will happen if we make the ground common for both?
please provide some references to understand it properly
thankyou.......
 

Harald Kapp

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can we connect power ground and micro controller ground?
It depends on your circuit and how you connect the two grounds.
  1. If you have isolated interfaces between µC and power (isolated inputs and/or outputs e.g. by using optocouplers and relays), then there is no need to connect the two different grounds. It may even have a negative effect as noise from power is coupled into the sensitive µC circuit.
  2. If there is no isolation between µC and power (e.g. output by a transistor, input by a resistive divider to match power voltage to µC voltage) then you absolutely have to connect the two grounds for correct operation. It is generally recommended to make this connection at only one point, the star point, which should be close to the power supplies.

Details can vary, depending on your specific circuit.
 

annapurna

Feb 3, 2017
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my power line has 400v, and 30A flows through it , is it necessary to isolate micro-controller ground to power ground? or if not isolated then what wil be the consequences?
 

Harald Kapp

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I can't tell you whether it is necessary to separate the µC circuit from the power circuit.
Technically it may work when not isolated. However, there are other considerations like e.g. safety standards and regulations to be observed. These are application specific.
It very much depends on whether the µC circuit can be touched or is conencted to another circuit that can be touched. A direct connection to the high voltage circuit will then pose a hazard to anyone coming in touch with the system.

For safety reasons it is much better to keep the high voltage circuit and the µC circuit isolated. The increase in safety is worth the increase in cost and size..
 

Minder

Apr 24, 2015
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It is done quite frequently in industrial control electronics where the DC power common is connected to earth ground, this however is commonly done with a star ground point, and/or something called equi-potential bonding, this is ensuring that all metallic parts are bonded to avoid ground loops.
I have a PDF on this by Siemens but it is too large to upload, they used to have it on their site but unfortunately it is no longer there since they revamped the site.
M.
 

Harald Kapp

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This explanation may come near to @Minder 's PDF.
Note that a common ground or earth is an idealized idea, working for DC and low currents only. At high frequencies and high currents you'll be able to measure voltage differences between different points of a supposedly common ground network. This is due to the impedances being > 0 Ω which leads to a voltage drop when current flows.

Also having everything connected to the same ground creates the potential for ground loops which can disturb the operation of an electronic system. Apart from safety (main reason) this is therefore another reason for using isolation: break ground loops.
 
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