Earth vs ground and spark gaps - Electronic Circuits Projects Diagrams Free

logicnibble · 25th June 2008, 05:17 PM

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 · 25th June 2008, 06:21 PM

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.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Latest
Constant ground to a triped ground?	misterpat	Electronic Projects Design/Ideas/Reviews	2	8th December 2007 12:35 AM
Simple (earth) ground tester	Marks256	General Electronics Chat	18	4th July 2007 10:13 PM
Earth ground on power supply question.	RDL2004	General Electronics Chat	3	9th February 2006 05:18 PM
Negative ground in series with Positive ground	walters	General Electronics Chat	18	14th December 2005 05:20 PM
What is Chassis Ground, Technical Ground, Circuit Ground?	victor	General Electronics Chat	2	28th October 2002 11:48 AM

25th June 2008, 05:17 PM	(permalink)
logicnibble	Earth vs ground and spark gaps 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?

25th June 2008, 06:21 PM	(permalink)
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. __________________ Carl