cupoftea
Advanced Member level 6
Hi,
I specified a NCP1239JD65R2G as a fifth source part in an offline 20W flyback.
(Ultimately this led to my employment termination.)
NCP12389
This was for a new board. (a new board where the old board had a different controller
which had gone obsolete)
The flyback is only for use at 200-265VAC, however, the test spec on production
requests it should start up at 90VAC. (for unknown, historic reasons)
NCP1239JD65R2G latchs off on overload. I had mistakenly missed this point in the datasheet.
My first source part (NCP1239ED65R2G) did not latch off like that.
Anyway, this flyback was also required by the customer to have a 50R NTC.
(which incidentally is 120R at zero degc, and 400R at -25degc).
Anyway, the guys on production somehow selected my fifth choice part for the production run, instead of
any of the first 4 alternatives which did not latch off.
From cold, in production test, they were fiddling with the variac around 90VAC, until they got it to start up and then latch off.
It was latching off on overload, because the cold NTC was dropping so much voltage that the flyback went into
overload and latched off.
This was deemed to be a very serious error on my part.
It was said that if a particular magnitude mains dip ever happened, and the NTC was initially cold,
and then the load also suddenly went no_load to full_load, then indeed the NCP1239JD65R2G may well latch off,
and the customer would then have to cycle the supply voltage on and off to get it working again.
So my question is, how common are mains dips of length 64ms or more?
In order to cause latch off, the mains dip would have also have to be above the Brown-out voltage of the
NCP1239JD65R2G....because then the chip wouldn't get chance to latch off on overload, as it would have turned
off (non latching) on brown out....and would then just start up again when the brown out ended. (ie no latch, no problem)
So really, I am asking, which are more common, "mains dips", or "mains total loss of cycles"?...since only a mains dip
>64ms and that remained above the brown out voltage would have caused the problem of latch off...and even then, only if the
NTC was cold and the supply suddenly went from no load to full load at the exact same time as the mains dip.
So, I am just trying to work out what inconvenience may have been caused to the customer?
The product is a lighting controller.
I was incidentally, employment terminated due to this mistake, but i am trying to work out
how commonly the problem would have happened? I'm under the impression that a consultancy who were
brought in to check my work has
well over-exaggerated the issue here, since they wanted to discredit me so they could garner future work for themselves.
I specified a NCP1239JD65R2G as a fifth source part in an offline 20W flyback.
(Ultimately this led to my employment termination.)
NCP12389
This was for a new board. (a new board where the old board had a different controller
which had gone obsolete)
The flyback is only for use at 200-265VAC, however, the test spec on production
requests it should start up at 90VAC. (for unknown, historic reasons)
NCP1239JD65R2G latchs off on overload. I had mistakenly missed this point in the datasheet.
My first source part (NCP1239ED65R2G) did not latch off like that.
Anyway, this flyback was also required by the customer to have a 50R NTC.
(which incidentally is 120R at zero degc, and 400R at -25degc).
Anyway, the guys on production somehow selected my fifth choice part for the production run, instead of
any of the first 4 alternatives which did not latch off.
From cold, in production test, they were fiddling with the variac around 90VAC, until they got it to start up and then latch off.
It was latching off on overload, because the cold NTC was dropping so much voltage that the flyback went into
overload and latched off.
This was deemed to be a very serious error on my part.
It was said that if a particular magnitude mains dip ever happened, and the NTC was initially cold,
and then the load also suddenly went no_load to full_load, then indeed the NCP1239JD65R2G may well latch off,
and the customer would then have to cycle the supply voltage on and off to get it working again.
So my question is, how common are mains dips of length 64ms or more?
In order to cause latch off, the mains dip would have also have to be above the Brown-out voltage of the
NCP1239JD65R2G....because then the chip wouldn't get chance to latch off on overload, as it would have turned
off (non latching) on brown out....and would then just start up again when the brown out ended. (ie no latch, no problem)
So really, I am asking, which are more common, "mains dips", or "mains total loss of cycles"?...since only a mains dip
>64ms and that remained above the brown out voltage would have caused the problem of latch off...and even then, only if the
NTC was cold and the supply suddenly went from no load to full load at the exact same time as the mains dip.
So, I am just trying to work out what inconvenience may have been caused to the customer?
The product is a lighting controller.
I was incidentally, employment terminated due to this mistake, but i am trying to work out
how commonly the problem would have happened? I'm under the impression that a consultancy who were
brought in to check my work has
well over-exaggerated the issue here, since they wanted to discredit me so they could garner future work for themselves.
