Hello Piotr,
I recommend using clause 2.5 as guidance. This clause describes limited
power sources for a different rating and purpose, but it can be used as
guidance as to the proper limiting of any power source.
It state that a power supply with a PTC will be considered limited if a
positive temperature coefficient device is used, as long as the PTC passes
the tests specified in IEC 60730-1, clauses 15, 17, J15 and J17.
Other methods may be used for impedance limiting, or you may use a
regulating network with an overcurrent protective device. The regulating
network may be used alone if the output still complies with the applicable
limits after any single fault.
Ted Eckert
American Power Conversion Corporation
The items contained in this e-mail reflect the personal opinions of the
writer and are only provided for the assistance of the reader. The writer
is not speaking in an official capacity for APC nor representing APC's
official position on any matter.
"Piotr Galka"
<piotr.galka@micr
omade.pl> To
Sent by: "EMC-PSTC" <[email protected]>
[email protected] cc
Subject
10/11/2006 07:54 EN 60950-1 Limiting power to 15VA
AM
Dear all,
Still trying to understand 60950-1.
How to limit power source to 15VA (Cl. 4.7.2.2) ?
A circuit powered from 12V (5A) source takes only 0.1A.
Do inserting one 0.1A PTC (or fuse) between source and circuit is enough.
When PTC is shorted the circuit takes 0.1A, when circuit has error the PTC
limits current to 0.1A.
But when PTC is shorted the sentence: "circuit is supplied by power source
which is limited to 15VA" is not true.
So I suppose two PTC in series are needed. Am I right ?
If one PTC is not enough, I suppose one PTC and 7805 (5V regulator with
internal current limiting) are enough.
The 7805 is not powered by power source limited to 15VA, but any circuits
after it are.
Am I right ?
Best Regards
Piotr Galka
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