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Electronics => Beginners => Topic started by: Phaedrus on September 05, 2013, 11:02:14 pm

Title: Strange PCB feature (PSU line filter)
Post by: Phaedrus on September 05, 2013, 11:02:14 pm

So I was dissecting a 700W ATX PSU, a very high end one, and found an unusual design feature. As you can see in the attachment, there are these unusual needle shaped solder points. These are across the windings of a common mode choke in the line filter, right before the bridge rectifier. I cannot fathom the purpose of this feature. I asked our consulting engineer with 25 years experience, and he has no idea either.

What's up with this?

Title: Re: Strange PCB feature (PSU line filter)
Post by: AlfBaz on September 05, 2013, 11:22:52 pm

Doesn't look like the picture uploaded properly

Title: Re: Strange PCB feature (PSU line filter)
Post by: Fsck on September 05, 2013, 11:31:17 pm

0kB photo.

Title: Re: Strange PCB feature (PSU line filter)
Post by: Phaedrus on September 05, 2013, 11:34:20 pm

Crap. I'll reupload when I get home.

Title: Re: Strange PCB feature (PSU line filter)
Post by: David_AVD on September 06, 2013, 12:18:03 am

Spark gap?

Title: Re: Strange PCB feature (PSU line filter)
Post by: free_electron on September 06, 2013, 12:39:53 pm

Flashover structure. This is a trick used to be able to pass Hipot testing.
During hipot testing they apply a few kilovolt and see if nothing explodes violently or sets on fire.

This structure sparks over and protects the rest. One side of the structure should have a path to the chassis or neutral, possibly via a second of those spark gaps.

This is common on off-line smps's.