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Swys
Joined: 22 Jul 2008
Posts: 11
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 10 Jun 2009 7:50 ade7753 |
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Hi all,
I have abandoned my quest to build an energy meter completely from scratch since I've found out that you get such nice energy meter IC's such as the ADE7753.
I now want to interface with this device with a PIC18F452 (primarily because this is the model I have lying around). I have one question...for now:
I am going to read the current with a CT and the voltage with a voltage divider. When I look on the datasheet (specifically figure 30) I see that they indicate that the ground of the voltage divider is the same ground of the line voltage. In other words it is the neutral line. As a matter of fact, it seems to me as if the ground of the whole device (digital and analog part) is connected to neutral. Iwould like to power this project with a seperate power source (regulated with an LM7805 regulator), but does this then mean that the negative of my battery, the ground of the regulator and microcontroller, etc. should be connected to neutral?
Thanks in advance for your help
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umery2k75
Joined: 19 Apr 2006
Posts: 378
Helped: 24
Location: Pakistan
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10 Jun 2009 9:24 ade7753 example |
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| If I'm not wrong, you mean by the voltage divider of PIN 7.It appears to me, by looking at PIN 11, it's a digital ground. I haven't read anything about this IC, I just looked at the Figure 30 of the ADE7753 Datasheet. This IC has sepearate analog and digital ground. You might be confusing a little bit. You can eventually add analog ground and digital ground at a point in the PCB layout, but it doesn't mean you need to connect the neutral with GND of 7805 regulator.
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Swys
Joined: 22 Jul 2008
Posts: 11
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10 Jun 2009 9:40 analog ground symbol |
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Thanks for your answer!
Yes, I mean the voltage divider on pin 7. The one thing confusing me, is that (if you look at pin 7), the power supply (line voltage) is then also connected to digital ground. Can it be that they mean it should be neutral?
If I connect the analog (neutral) and digital grounds on the PCB layout, doesn't that mean (in effect) that the regulator, battery, micro, etc. is then connected to neutral?
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umery2k75
Joined: 19 Apr 2006
Posts: 378
Helped: 24
Location: Pakistan
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10 Jun 2009 21:19 microcontroller ade7753 |
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To explain you, I have given an example of ADC IC. In my diagram, the symbol is given wrong for analog ground. It's the symbol for Earth, but I have seen people using analog ground symbol,digital ground symbol and earth symbol using interchangeably.
Generally speaking, there is no difference between a digital ground and analog ground, both are the same. For your case, both will be connected to the regulator GND. So the question arises, if digital ground and analog ground are the same? So why people refer to them seperately. The answer lies in the layout of the PCB. In order to reduce noise, people seperates the GND in the PCB and reconnects the GND near the regulator(if using).Suppose you have a digital IC that's switching at 1Mhz, and a MIC. It's not good idea to connect the MIC GND with that IC GND. So, they name them as GND1=Digital Ground, GND2=Analog Ground. GND1=Uses high speed digitial circuitry(for example), GND2=Using low speed circuit(for example). More over it depends on the application.You will try to keep the power supply seperate for digital and analog circuitry, so as to reduce undesired results.
Neutral is entirely different from the analog ground. You can although connect digital ground,analog ground,neutral together, but you have to be very careful when doing so. Normally it's not done so. There's a technique in doing so. They cannot be connected together. What if the next time, you plug in to the wall recepticle with neutral and phase interchange. Your circuit would be BOOMED! I have seen few designers in which people using isolation transformer, in the first stage and so on...... I would not go into the detail of this, it's a seperate topic.
The word neutral is not used when refering to the GND of analog and digital supplies.It's used when we are referring to the AC Main Incoming power. Mine is 415V, 3 phase, Y connected with neutral, per phase 240V. Neutral is the name of the additional wiring coming from your electric company transformer near to your home.You electric company transformer will usually be fed with a delta wiring.It would be delta-Y transformer.
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