What is the purpose of a common ground connection in power supplies?

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Discussion Overview

The discussion revolves around the purpose of a common ground connection in power supplies, particularly in the context of circuits involving operational amplifiers and measurement equipment like oscilloscopes. Participants explore the role of common ground in circuit design and its relationship to positive and negative voltage rails.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants note that many power supplies feature a positive and negative output, with a common ground connection, but seek clarification on its specific purpose.
  • One participant suggests that a common ground may be connected to the negative rail, indicating a potential design choice.
  • Another participant describes a scenario involving an op-amp circuit, questioning whether it is necessary to use the common ground for all components or if the negative rail could suffice.
  • A distinction is made between standard power supplies and split rail supplies, which are designed for components requiring both positive and negative voltage rails.
  • There is mention of the flexibility in connecting the 0V rail to chassis ground, depending on the circuit designer's intent.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the function of common ground, with some clarifying its use in specific contexts while others remain uncertain about its necessity in all applications. The discussion does not reach a consensus on the best practices for using common ground in different circuit designs.

Contextual Notes

Participants reference specific circuit examples and design choices, but there are unresolved questions about the implications of using common ground versus negative rails in various scenarios.

matinm90
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Okay so I've seen that some not all power supplies have a positive and negative side for the voltag output and in addition have a common ground connection, exactly what is that used for?
 
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matinm90 said:
Okay so I've seen that some not all power supplies have a positive and negative side for the voltag output and in addition have a common ground connection, exactly what is that used for?

Ohhhh ? like to show an example of one that doesn't :)
All the many and varied PSU's I have worked with over the last 40 years all have a positive and negative output. bit difficult to complete a circuit without a negative rail ;)
Some may also have a ground/chassis connection and that connection may or may not be commoned with the negative

Dave
 
Lol let me explain that differently, all of the power suPplies I've seen have a positive and a negative, and some also have standalone ground connection or common ground, so what is it exactly? I know what ground is but what is a "common" ground for?
 
matinm90 said:
Lol let me explain that differently, all of the power suPplies I've seen have a positive and a negative, and some also have standalone ground connection or common ground, so what is it exactly? I know what ground is but what is a "common" ground for?

ok it may be as said in the last part of my comments.

a common ground may be connected to the negative rail.

do you have any circuit examples to look at and confirm ?

D
 
Some what, an op-amp circuit. The positive and negative feed the power for the op amp while the common ground, is used to ground the rest of the components that may be used, such as a function generator or oscilloscope, now is it necessary to use common ground for everything else? Or can we just use the low Potential or - for everything?
 
Ahhh ok

in that case its a little bit different, as its not the standard + and - rails where the ground and/or chassis is connected to the negative. Thats a split rail supply. Its specifically designed for components that need to work with a positive and negative rail, say +12 and -12 Volts. Other parts of the circuit may well just use the +12v and 0V rails

Now that 0V rail may or may not be connected to chassis ground. Thats really up to the designer of the circuit and what they are trying to achieve.

Dave
 
Ohh Okay. Well thank you that cleared things up for me, I appreciate it :-)
 
...For your oscilloscope testing you would use the 0V for the GND lead of the scope and the probe is free to measure voltages that may be more positive or more negative than the 0V rail.
 

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