Earth vs ground and spark gaps

[logicnibble]

Hi!

I'm designing a uC circuit which uses AC power: a simple transformer + diode bridge + capacitor + LM317 (3.3V).

I have some input connectors where it's supposed to read analog voltage and I want to protect them from ESD. For that I have thought using pcb spark gaps.
(see ESD and EMI protection in PCB Layout)

Since the spark gap is supposed to be connected to earth, Can I connect circuit ground to earth? That is, connect the reference from LM317 to earth from the mains plug?

 

[crutschow]

As the article notes, the spark gap is supplemental ESD protection for high voltages (above 2000V). You still need other protection for lower voltages: RC input filters, zener diodes, etc. to protect sensitive semiconductor inputs, some of which can be damaged by 10V or less.

This protection is local to the board's common return so it's not absolutely necessary to connect the board common to earth common. Sometimes this can cause ground loop noise problems. But it's generally good practice to have the chassis of your system connected to the main's earth ground (not electrical common) connection. That way if there's any fault to the chassis no one will be shocked.

 

[Sadanand]

ESD protection

Hi carl and everyone,
I am working on a analog project. The microcontroller has inbuilt adc.
I have read at every places to use the clamping diodes for esd protection.
So that the esd spike will get the bypass path to either Vcc or GND and thus protect the analog circuit. But problem is when the esd spike takes on the Vcc, it means that the supply of the microcontroller,Vcc, or the whole circuit is in terms of kV (Though for the fraction of a second). This will cause the problem to the microcontroller ( or any other sensitive ics ) which is very succeptible to the high voltage. So how to avoid the damage of the microcontroller.

 

[Sceadwian]

A good case with good grounding. Simply, don't give the ESD a path to the part in question, let it find a much better path to a local off circuit ground. Heavy metallic cases can help overall system grounding, but against high energy discharges a whole different set of rules apply, in fact there are really no 'rules' for high energy discharges.