Re: Gap, Creepage and Clearance for HF HV

Line-op stuff I see often has wide spacing (>0.2", I guess) and notches
punched out of the board to eliminate creepage as such entirely. At least,
the better stuff.

True, you may not have the luxury of that much space.

Tim

--
Deep Fryer: A very philosophical monk.
Website @ http://webpages.charter.net/dawill/tmoranwms

"D from BC" <myrealaddress@xxxxxxxxx> wrote in message
news:5nkpd399jf9g58e6i3j150gu8stu54l1h7@xxxxxxxxxx
On Mon, 03 Sep 2007 04:44:20 -0700, ChairmanOfTheBored
<RUBored@xxxxxxxxxxxxxxx> wrote:

On Mon, 03 Sep 2007 07:25:37 GMT, D from BC <myrealaddress@xxxxxxxxx>
wrote:

Huhhhh...My smps design did a little plasma show....zzzzzzzzz
then the power mosfet shorted out..
then the fuses blew.. :(
I suspect arcing somewhere perhaps due to not enough PCB trace to
trace clearance. (Just trying to increase PCB density...)

I have about 300Vpk @ 700Khz square wave areas on the PCB....

I know air breakdown depends on gap and voltage, but does air
breakdown voltage also depend on frequency?

(Assume humidity, pollutants or gases like N2,CO2,O2 are constant.)

D from BC


How long did it run before the failure mode occurred?

If it ran for a long period, then the solution is to conformally coat
the assembly (while it is new, of course).

Air ionization will eventually lead to carbon trail forming.

This is one reason why the long ceramic insulators on high tension
lines need to be changed out periodically. They eventually form carbon
trails on their surface, and all the creepage distance in the world wont
stop that resistor from conducting.

1 to 2 seconds. Probably closer to 1 second.
The arc started when I switched on the power.

It's probably a combo of traces too close together with flux on the
pcb.

But from I've read so far, it looks like I have to do my trace spacing
not only to prevent arcing but also to prevent eventual arcing.

More complications for the pcb layout. Arrrghhh :(
D from BC


.

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