PCB improvements and tips
Didan , 07-09-2019, 12:34 PM
Dear forum, I would like to ask for help to analyze this layout ive done. Its a 3 phase energy meter and we have a high voltage input 230 AC passing through varistor to protect against voltage surge and there are resistor chain to decrease voltage from 230AC and a voltage divider to condition signal and go to metering chip ... What i already now is that for high voltage designs I need to keep a creepage distance between components pad at least 0.8mm for coated pads, its from IPC 2221 to avoid arcs between then. Another point is avoid routing low voltage signals close to high voltage signals.
I would like to say that I worked with restricted area size, because this board must have this dimensions and have pin headers exactly on that position, because its a module going on another board...
I will have 3 types os current transformer (CT) selection, 5A secondary, 1A secondary and 50mA. As I have CT, after these shunt resistor I will convert current in voltage and I still need to condition signal for energy metering chip. Im ok about hardware project and calculations my doubt is about LAYOUT on this board because thats my second version of this board and I improved so much... Anyway I would like to hear what to improve. I know I have some vias under energy metering chip, its not microcontrooler or processor, only a chip... I placed all decoupler capacitors and components closer to it as well crystal on the same layer as you can see on pictures. I tried do my best with all my experience with restricted size so if someone with more experience here mainly in high voltage boards, let me know where to improve... Ive been following all good hardware practices and high voltage as well but I know as I was saying vias under chip i couldnt avoid, its really tight layout but I thought I did a good job, but as always, its important to hear from experienced hardware engineers...
I know that my track for current transformer isnt wide enough as well, its to withstand 5A but its AC current, not DC current. I have some doubts about it, DC currents and AC current width tracks are different for same voltage, right? I couldnt find any table or calculator like saturn pcb i dont know how to use well or online calculators, but im using 50 mil track for 5A CT.
I would like to say that I worked with restricted area size, because this board must have this dimensions and have pin headers exactly on that position, because its a module going on another board...
I will have 3 types os current transformer (CT) selection, 5A secondary, 1A secondary and 50mA. As I have CT, after these shunt resistor I will convert current in voltage and I still need to condition signal for energy metering chip. Im ok about hardware project and calculations my doubt is about LAYOUT on this board because thats my second version of this board and I improved so much... Anyway I would like to hear what to improve. I know I have some vias under energy metering chip, its not microcontrooler or processor, only a chip... I placed all decoupler capacitors and components closer to it as well crystal on the same layer as you can see on pictures. I tried do my best with all my experience with restricted size so if someone with more experience here mainly in high voltage boards, let me know where to improve... Ive been following all good hardware practices and high voltage as well but I know as I was saying vias under chip i couldnt avoid, its really tight layout but I thought I did a good job, but as always, its important to hear from experienced hardware engineers...
I know that my track for current transformer isnt wide enough as well, its to withstand 5A but its AC current, not DC current. I have some doubts about it, DC currents and AC current width tracks are different for same voltage, right? I couldnt find any table or calculator like saturn pcb i dont know how to use well or online calculators, but im using 50 mil track for 5A CT.
Didan , 07-09-2019, 02:17 PM
some additional pictures. I placed gnd planes on board. I know I must need gnd plane and high voltages sepparated at least 0.8mm for insulation. As well pin header with 3 pins, gonna have AC voltage thats why I isolated it. However I have a big doubt about current transformer, high current track and gnd plane or vias close to it, i dont know how to proceed very well..
Lakshmi , 07-12-2019, 04:39 AM
- Please try to write in points don't write as essay It's hard to read and reader won't be interested.
- What's the track width you've have used for AC Signal?
- Make sure you use more than 1.5mm for all AC Signal.
- Yes, Track width should be different for AC and DC.
- Make sure you've solid gap between Digital GND and AC.
- What's the track width you've have used for AC Signal?
- Make sure you use more than 1.5mm for all AC Signal.
- Yes, Track width should be different for AC and DC.
- Make sure you've solid gap between Digital GND and AC.
Comments:
Didan, 07-12-2019, 01:35 PM
Lakshmi. Can you share important articles, pdfs, your experience what you have done and worked doing what you are suggesting for my board, stuffs like that please? -AC signal track width: 50 mils-Well about 1.5mm is based on IEC-61010 ? Because from IPC2221 its saying 0.8mm. Its a good point of discussion i dont have sure which one to follow and if you have knowledge on it let me know.-AC and DC track should be different, so tell me how different they need to be and which part of circuit if you identified it.- solid gap between digital gnd and AC its important, how much gap? 30 mil? I set 30 mil for my gnd plane on bottom and top
Paul van Avesaath , 07-12-2019, 07:20 AM
is making the board larger an option? so you can put more space between dc and ac?
Comments:
Didan, 07-12-2019, 01:28 PM
unfortunately I cant resize board, it must need be as it is. I have restrictions on size and pin headers as well phoenix connectors bust be where they are... its a module so is it ok at least 0.8mm isolation for ac and gnd ? I was following ipc 2221...
Lakshmi , 07-13-2019, 12:02 AM
you can have a quick look at this :
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