“The small partners who are doing power research and development must have heard that do not connect the wrong ground. The ground of the capacitor behind the rectifier bridge and the ground cannot be connected together, otherwise it will cause a short circuit. I just wanted to understand this issue today, so I’ll record it, and I hope you can correct me if I’m wrong.
“
The small partners who are doing power research and development must have heard that do not connect the wrong ground. The ground of the capacitor behind the rectifier bridge and the ground cannot be connected together, otherwise it will cause a short circuit. I just wanted to understand this issue today, so I’ll record it, and I hope you can correct me if I’m wrong.
First look at the schematic diagram of AC-DC (full wave rectification):
Let’s take a look at the action process of the rectifier bridge when the input terminal is AC220V:
1. When AC220V is a positive half cycle, the ground of the filter capacitor C4 after the rectifier bridge is connected to the neutral line N, and the ground of the filter capacitor C4 is connected to the ground at this time.
As shown below:
2. When the AC220V is a negative half cycle, the ground of the filter capacitor C4 after the rectifier bridge is connected to the live wire L, and the ground of the filter capacitor C4 is connected to the live wire at this time.
As shown below:
We know that the potential of the earth (PE) is 0V, then the voltage waveform of the negative electrode (GND) of C4 from the earth is the following blue line:
From the above figure, we can see that during full-wave rectification, the GND of the filter capacitor C4 has a voltage relative to the ground (PE), so connecting the two together will of course cause a short circuit.
So the GND after full-wave rectification is also very dangerous~ This may also be the reason why it is called “hot ground”.
Let’s continue to look at the schematic diagram of the non-isolated BUCK circuit:
We can see that the GND of the low-voltage 12V output is connected to the GND of the filter capacitor at the input end, so in the non-isolated buck circuit, when the input end is full-wave rectification, the ground on the low-voltage side is also “hot ground”. It’s very dangerous~
Take a look at the BUCK schematic of the isolation style:
We can see that the GND of the low-voltage output side is isolated from the GND of the input filter capacitor, and the low-voltage side is equivalent to being powered by the secondary winding (the secondary winding can be regarded as a battery). At this time, the ground of the low-voltage side is equivalent to Floating (floating), the low-voltage side is relatively safe at this time, so the GND of the low-voltage side should be connected to the ground~
The above is the full-wave rectification state. Let’s think about it again. What if it is half-wave rectification?
In the negative half cycle of AC, there is no path in the loop, and the GND of the filter capacitor C4 is equivalent to floating. When the positive half cycle of AC arrives, it will be reconnected to the ground (PE).
So in the circuit of half-wave rectification, the rectified ground seems to be safe, is that the case?
I think it’s fine and safe if the live and neutral wires are connected to the grid correctly.
but. . . Once our plug is reversed, that is, the live wire L in the circuit is connected to the N in the power grid, and N is connected to the L of the power grid, (this may happen in actual use)
At this time, the rectified ground is connected to the live wire of the grid. . . So it is also very dangerous.
Therefore, the ground after half-wave rectification is also a “hot ground”, which is very dangerous.
Finally to sum up:
1. Whether it is full-wave rectification or half-wave rectification, the rectified ground is “hot ground”
2. There is a voltage between the “hot ground” and the ground, and they cannot be connected together, which will cause a short circuit.
3. The power ground converted by the non-isolated DCDC is also a “hot ground”.
4. After the isolated DCDC conversion, the ground on the low-voltage side is “floating ground”. I think the “floating ground” can be connected to the ground.
The above is a little bit of my experience, please advise~
—————————————————————
Copyright statement: This article is an original article by CSDN blogger “Planet One”, which follows the CC 4.0 BY-SA copyright agreement. Please attach the original source link and this statement for reprinting.
Original link: https://blog.csdn.net/weixin_45925764/article/details/114684870
“The small partners who are doing power research and development must have heard that do not connect the wrong ground. The ground of the capacitor behind the rectifier bridge and the ground cannot be connected together, otherwise it will cause a short circuit. I just wanted to understand this issue today, so I’ll record it, and I hope you can correct me if I’m wrong.
“
The small partners who are doing power research and development must have heard that do not connect the wrong ground. The ground of the capacitor behind the rectifier bridge and the ground cannot be connected together, otherwise it will cause a short circuit. I just wanted to understand this issue today, so I’ll record it, and I hope you can correct me if I’m wrong.
First look at the schematic diagram of AC-DC (full wave rectification):
Let’s take a look at the action process of the rectifier bridge when the input terminal is AC220V:
1. When AC220V is a positive half cycle, the ground of the filter capacitor C4 after the rectifier bridge is connected to the neutral line N, and the ground of the filter capacitor C4 is connected to the ground at this time.
As shown below:
2. When the AC220V is a negative half cycle, the ground of the filter capacitor C4 after the rectifier bridge is connected to the live wire L, and the ground of the filter capacitor C4 is connected to the live wire at this time.
As shown below:
We know that the potential of the earth (PE) is 0V, then the voltage waveform of the negative electrode (GND) of C4 from the earth is the following blue line:
From the above figure, we can see that during full-wave rectification, the GND of the filter capacitor C4 has a voltage relative to the ground (PE), so connecting the two together will of course cause a short circuit.
So the GND after full-wave rectification is also very dangerous~ This may also be the reason why it is called “hot ground”.
Let’s continue to look at the schematic diagram of the non-isolated BUCK circuit:
We can see that the GND of the low-voltage 12V output is connected to the GND of the filter capacitor at the input end, so in the non-isolated buck circuit, when the input end is full-wave rectification, the ground on the low-voltage side is also “hot ground”. It’s very dangerous~
Take a look at the BUCK schematic of the isolation style:
We can see that the GND of the low-voltage output side is isolated from the GND of the input filter capacitor, and the low-voltage side is equivalent to being powered by the secondary winding (the secondary winding can be regarded as a battery). At this time, the ground of the low-voltage side is equivalent to Floating (floating), the low-voltage side is relatively safe at this time, so the GND of the low-voltage side should be connected to the ground~
The above is the full-wave rectification state. Let’s think about it again. What if it is half-wave rectification?
In the negative half cycle of AC, there is no path in the loop, and the GND of the filter capacitor C4 is equivalent to floating. When the positive half cycle of AC arrives, it will be reconnected to the ground (PE).
So in the circuit of half-wave rectification, the rectified ground seems to be safe, is that the case?
I think it’s fine and safe if the live and neutral wires are connected to the grid correctly.
but. . . Once our plug is reversed, that is, the live wire L in the circuit is connected to the N in the power grid, and N is connected to the L of the power grid, (this may happen in actual use)
At this time, the rectified ground is connected to the live wire of the grid. . . So it is also very dangerous.
Therefore, the ground after half-wave rectification is also a “hot ground”, which is very dangerous.
Finally to sum up:
1. Whether it is full-wave rectification or half-wave rectification, the rectified ground is “hot ground”
2. There is a voltage between the “hot ground” and the ground, and they cannot be connected together, which will cause a short circuit.
3. The power ground converted by the non-isolated DCDC is also a “hot ground”.
4. After the isolated DCDC conversion, the ground on the low-voltage side is “floating ground”. I think the “floating ground” can be connected to the ground.
The above is a little bit of my experience, please advise~
—————————————————————
Copyright statement: This article is an original article by CSDN blogger “Planet One”, which follows the CC 4.0 BY-SA copyright agreement. Please attach the original source link and this statement for reprinting.
Original link: https://blog.csdn.net/weixin_45925764/article/details/114684870
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