Is it ok to place AT89S52 microcontroller very close to the stepdown transformer?

[Hiroshi_S]

hi,
My PCB size is compact and so i am placing the microcontroller AT89S52 near the transformer, I am worried about its working. I want to know will this design will disrupt the normal working of the microcontroller? Kindly give your valuable feedback.

 

[MD_SHAHRUKH]

Can you share with us your PCB design image?

 

[Hiroshi_S]

Can you share with us your PCB design image?

Here I have provided the sample placement

 

[MD_SHAHRUKH]

What kind of transformer is it? A PCB mount flyback transformer(SMPS transformer)? Size? Distance between the transformer and your microcontroller?

 

[Hiroshi_S]

What kind of transformer is it? A PCB mount flyback transformer(SMPS transformer)? Size? Distance between the transformer and your microcontroller?

Its PCB mount metallic core single phase transformer of 200mA stepped down to 18V, its size is 22x38 and, its distance between uC and transformer is hardly 3mm. and there are relays too in the design.

 

[KlausST]

Hi,

The problem I see is not the transformer, but the PCB is not made according EMI/EMC and ESD standards.

Nowadays circuits are used nearby HF sources like cellular phones, WiFi, Bluetooth...thus - because of lack of a GND plane - all traces will act as transmitting and receiving antennas.
Then there is a connector where directly microcontroller signals are wired to. I see no ESD protection nor HF filters.

Let's imagine the transformer as a car with thieves (HF noise) close to your house. But your PCB (house) circuit is an "invitation" for thieves with open doors (no protection).

Klaus

Btw: since decades computers usually have a "screenshot button" no need to take photos with bad quality and big file size.

 

[Hiroshi_S]

Hi,

The problem I see is not the transformer, but the PCB is not made according EMI/EMC and ESD standards.

Nowadays circuits are used nearby HF sources like cellular phones, WiFi, Bluetooth...thus - because of lack of a GND plane - all traces will act as transmitting and receiving antennas.
Then there is a connector where directly microcontroller signals are wired to. I see no ESD protection nor HF filters.

Let's imagine the transformer as a car with thieves (HF noise) close to your house. But your PCB (house) circuit is an "invitation" for thieves with open doors (no protection).

Klaus

Btw: since decades computers usually have a "screenshot button" no need to take photos with bad quality and big file size.

Thanks, Klaus... well, I will consider your views. once it's done, I will send the proper screenshots.
Thanks lot.

 

[FvM]

Distance between mains transformer and uC is no particular problem. I expect disturbed processor operation caused by relays arcing. Also noise coupled through transformer winding capacitance to the processor circuit might be a problem. Poor ground wiring and insufficient 5V bypassing allow inferences to pass to the processor and e.g. cause unintended resets.

 

[zenerbjt]

You do not show schem...if you show it, more advice can flow to you.Your is a mains transformer so its a bit noisy with the rectifier switching etc, but not as bad as a smps transformer.
Incidentally, attached is PCB layout notes.
Basically.
Keep current loops as narrow in area as possible.
Dont run switching power currents along lengths of control ground otherwise you get ground bounce and the ground varies in potential and processors may get upset.
Keep switching nodes (high dv/dt) as small as possible......or shield them with ground copper or DC rail copper

--- Updated Dec 26, 2020 ---

And i will finish off with a question for you. Why should PCB track current loops be kept as small in area as possible? Especially current loops which involve connections to sensitive inputs or processors etc.
Remember a current loop can be through a capacitor in places.