Offline isolated flyback track/pad clearances on PCB?

[Faringdon]

Hi,
Would you agree, if doing an offline isolated flyback of 90-265vac, then the minimum  number of net class's that you can get away with , when laying out the PCB,  is ten?
The net class's are necessary, ayk, so that you can get the correct clearancing between the various nets. Some nets will obviously be in 2 or more of the net class's.

(If you like , Take a 84/19 transformer, 20W and 24vout and 65khz, or therabouts.)

[Gyro]

So one day you troll us again (the Cheap Chinese EV thread) and a couple of days later you're back again asking for technical help on something you should already know to do your job, according to your career history?

I don't think that's the way it works. 

[ebastler]

Would you agree, if doing an offline isolated flyback of 90-265vac, then the minimum  number of net class's that you can get away with , when laying out the PCB,  is ten? [...]
Some nets will obviously be in 2 or more of the net class's.

Where did you pull the number "ten" from?
And what EDA system do you use which lets you assign a net to multiple net classes?

Edit: Ah, seems that Altium lets you do that, since it uses net classes for other grouping beyond physical attributes of the trace. What happnes if the net classes defne conflicting physical properties? Largest trace width, clearance etc. wins?

[T3sl4co1l]

Shrug, I mean I have a design running currently with 16 clearance rules, which only roughly captures the creepage and clearance required in the design spec.  As you know, Altium doesn't understand creepage so that has to be handled by manual inspection (at this stage, anyway), and several other clearances I've handled by inspection as well.

Driving those rules, I have six net classes, and somewhat unrelated, three pad classes.  (Plenty of component classes, but I never use those anyway.)

Tim

[tom66]

Where does the requirement for using any number of net classes come from?  There's no requirement to use net classes in Altium, you can set traces to any width you want and you can use polys for large power planes...  so the minimum number is zero and the maximum number could be 50, if you wanted to be really anal about your power track widths, for instance.

[PlainName]

There's no requirement to use net classes in Altium, you can set traces to any width you want and you can use polys for large power planes...

The classes would be used to specify the clearance (and probably width, but that's not the important factor here, I think).

[tom66]

There's no requirement to use net classes in Altium, you can set traces to any width you want and you can use polys for large power planes...

The classes would be used to specify the clearance (and probably width, but that's not the important factor here, I think).

Point is, you could do the clearances manually.  There's no requirement to set that up, it's just going to make your life so much easier if you do.

[Faringdon]

Where did you pull the number "ten" from?

Thanks, the attached diagram.
I am sure all would agree that at least these net class's (12 shown here) are  absolutely needed in  order to properly get the right clearancing/creepaging between the various nets.
Without the shown class's, the job just can't be done properly.....your layout will either be too big, or you will violate clearance rules.

Though good luck in finding  what EN62368 or IPC2221 says about these clearances, because none of the regulations define all the spacing between all the shown nets here.
So we are on our own.....no guidance.
The only guidance you have is that clearance/creepage from Line to Neutral, upstream of the fuse, should be at least 2.5mm.
Anything else...take a guess.....though if its not the right guess, then some lawyer could call in a total product recall for you, since its open to interpretation.

[mtwieg]

It would be pretty wild if Intertek/TUV/UL asked how many constraint classes you used in designing the PCB.

Though good luck in finding  what EN62368 or IPC2221 says about these clearances, because none of the regulations define all the spacing between all the shown nets here.
So we are on our own.....no guidance.

Safety standards don't exist to do your designs for you.

The only guidance you have is that clearance/creepage from Line to Neutral, upstream of the fuse, should be at least 2.5mm.
Anything else...take a guess.....though if its not the right guess, then some lawyer could call in a total product recall for you, since its open to interpretation.

Typically I think one would have their design reviewed and certified by a notified body before selling or marketing a device, making this unlikely.