# EMC Design Precaution

I'm designing a simple circuit which will charge a big capacitor for 3 seconds, then pass a 5A current for few microseconds, then charge again the big capacitor for 3 seconds, then pump again 5A for a few microseconds, and so on. And now I test it on a breadboard and I'm convince that its working. So I started to do a PCB layout.

Questions are the following:

1. Do I need to concerned on the EMI emission?
2. What design techniques can you recommend to me or PCB guide layout on this specific PCB.
3. Any precaution that I need to do in the circuit or even PCB layout?
• Sharing your schematic will help formulate good answers. Also, is the circuit going to pass 5 Amperes "for few Microseconds" or "for 3S"? Contradictory information in the question. Jan 31 '13 at 5:35
• Is 3s the repetition period of pulses? Jan 31 '13 at 6:00
• It will pump 5A for few microseconds and this scenario will be repeated after 3S.
– jasp
Jan 31 '13 at 8:38
• It will better if you can explain more about the schematic. Could include a capture of the schematic? Jan 31 '13 at 10:58
• What is the different between 2nd and 3rd question? Jan 31 '13 at 10:59

1.- Yes, sure. You always must attend the EMC performance of your electronics design.

EMC or Signal Integrity, we are talking about the same. Although probably It's a hobbyist-project and you won't need to pass an emission or immunity EMC test in a EMC Lab but EMC is also the noise, the crosstalk or ground bounce and this could be a problem inside your project.

So, yes. For emission you can check: (only a summary)

• Raise/Fall Time in high speed signals.
• Layout of high speed. (Changes of layers, loop current...)
• Possible antennas. (Your connector and your cables could work as an antennas)

2.- It would better if you explain us more about your circuit.

I suppose there is a component that works as a switch. The out of this component we can call it "switch node". In this node the voltage is

$$V = L (di/dt)$$

; V is voltage, L the inductance of the node, i is the current, and $$di/dt$$ is the rise time (or fall time) of change.

This parameter is really important!

Maybe you can:

• Decrease the rise time. (Could it work slower?)
• Decrease the voltage (Could you use a lower voltage?)
• Decrease the inductance in your switch node.
• Include a snubber (a circuit for absorb the voltage peak).

3.- This question is the similar to 2 isn't it?