On Fri, 19 Apr 1996, Kendall Wilcox wrote:
> I was discussing UL 1950/CSA950/EN60950 clause 2.11, Limited Power
> Source with a colleague, and we were looking at the Table 9 limits for
> maximum output current Isc (1000/Uoc) and maximum VA (250). If Uoc is
> 20V, then Isc is 1000/20 = 50A max. However, 20V X 50A = 1000VA.
If Uout=Uoc is 20V then the current is zero and 0VA, if short
circuit,then Isc is 50A and Uout is 0V, again 0VA. THe maximum power is
available in the middle, 10V with 25A and that is 250V.
The assumption is that the power source has a resitor limited output
current.
Rgds,
Rene
> It seems like if the maximum allowable VA is 250 and Uoc is 20V, then
> the maximum current is limited to 250/20 = 12.5A.
>
> I probably can't see the forest for the trees, but unfortunately my
> brain is supplied by a limited power source. Any comments as to why
> there is my perceived discrepancy between Isc and max VA would be
> appreciated.
>
>
> Just Wonderin',
>
> Kendall Wilcox
> Manager, Regulatory Engineering
> Fujitsu Computer Products of America
> [email protected]
>
>
