Chengjun Li
- Oct 21, 2014
- 84
- Joined
- Oct 21, 2014
- Messages
- 84
Hi, I have a question about some materials I've read in terms of grounding. Below is the material.
"
III An Illustration of a Typical Power Supply Grounding Error
As previously pointed out, the ground symbol, in many cases, has been taken as a generic symbol in electronic circuit diagrams to represent the current return path, even though no physical earth ground is used. This can cause some confusion to the novice engineering student when using instruments having an earth ground terminal. As an example, Figure 3 shows the front panel of a typical power supply. The supply is represented as a variable voltage battery. Note that three terminals are shown: a positive, a negative, and a ground terminal. The ground terminal of the supply is tied to the case of the instrument, which in turn is wired to a true earth ground such as a water pipe.
Let's look at the load connection in Figure 3. Using the positive terminal of the battery and the ground terminal does not complete a current return path to the energy source (battery), so no current will flow from the source, i.e.
Iload = 0.
Figure 3 A Common Power Supply Grounding Error
The positive and negative terminals must be used to have a return path exist. Use of the ground terminal will be discussed in a following section.
Many circuits require both positive and negative voltages. A power supply must be used to provide each polarity. The supply for positive voltage will have the negative terminal as a return, and the negative supply will have the positive terminal as the return. These two terminals are connected together, forming a common return path for load current. Figure 4 shows
the proper connections for these supplies to provide positive and negative voltages.
Figure 4 Power Supply Configuration for Dual Polarity Voltages
Although it may be shown as a ground in the circuit diagram, the connection between the negative and positive terminals of the supplies results in a common, or floating, return. If students feel that they must faithfully adhere to the circuit diagram, the floating common may be connected to the earth ground terminal of the supply. Generally, it will neither help nor hinder circuit performance."
The first question is why the author says the floating common can be connected to earth ground while it won't influence the circuit performance?If the common is connected to earth ground, then it is no longer a floating source,right? Another question is from the material, it seems this kind of power supply is a floating one. I happened to find such an power supply, I set the voltage level the same with a battery and connected it to a circuit, but the performance is different from the battery, Why? Maybe it is not a floating power supply as the author says.
"
III An Illustration of a Typical Power Supply Grounding Error
As previously pointed out, the ground symbol, in many cases, has been taken as a generic symbol in electronic circuit diagrams to represent the current return path, even though no physical earth ground is used. This can cause some confusion to the novice engineering student when using instruments having an earth ground terminal. As an example, Figure 3 shows the front panel of a typical power supply. The supply is represented as a variable voltage battery. Note that three terminals are shown: a positive, a negative, and a ground terminal. The ground terminal of the supply is tied to the case of the instrument, which in turn is wired to a true earth ground such as a water pipe.
Let's look at the load connection in Figure 3. Using the positive terminal of the battery and the ground terminal does not complete a current return path to the energy source (battery), so no current will flow from the source, i.e.
Iload = 0.
Figure 3 A Common Power Supply Grounding Error
The positive and negative terminals must be used to have a return path exist. Use of the ground terminal will be discussed in a following section.
Many circuits require both positive and negative voltages. A power supply must be used to provide each polarity. The supply for positive voltage will have the negative terminal as a return, and the negative supply will have the positive terminal as the return. These two terminals are connected together, forming a common return path for load current. Figure 4 shows
the proper connections for these supplies to provide positive and negative voltages.
Figure 4 Power Supply Configuration for Dual Polarity Voltages
Although it may be shown as a ground in the circuit diagram, the connection between the negative and positive terminals of the supplies results in a common, or floating, return. If students feel that they must faithfully adhere to the circuit diagram, the floating common may be connected to the earth ground terminal of the supply. Generally, it will neither help nor hinder circuit performance."
The first question is why the author says the floating common can be connected to earth ground while it won't influence the circuit performance?If the common is connected to earth ground, then it is no longer a floating source,right? Another question is from the material, it seems this kind of power supply is a floating one. I happened to find such an power supply, I set the voltage level the same with a battery and connected it to a circuit, but the performance is different from the battery, Why? Maybe it is not a floating power supply as the author says.
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