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-48V inrush current requirements

A

Allan Herriman

Jan 1, 1970
0
Hi,

I'm trying to determine which Telcordia requirement document specifies
the allowable inrush current on -48V inputs of equipment.

I tried searching the Telcordia website without any luck. Can anyone
help?
I also tried asking in comp.dcom.telecom.tech and didn't get a single
reply.


BTW, other (non-US) specifications that I already have are ETSI EN 300
132-2 (applies in Europe) and Telstra 1555 (applies in Australia).

Thanks,
Allan.
 
T

Tim Shoppa

Jan 1, 1970
0
Allan Herriman said:
Hi,

I'm trying to determine which Telcordia requirement document specifies
the allowable inrush current on -48V inputs of equipment.

I tried searching the Telcordia website without any luck. Can anyone
help?
I also tried asking in comp.dcom.telecom.tech and didn't get a single
reply.

I'm not a Telcordia standards expert... but I'm not even sure which end
of the problem you're looking at. Are you trying to prevent the central
switch from thinking that you've gone "offhook" when really you're just
charging a capacitor? Generally there's an impedance you have to stay
above (almost equivalently, a current you have to stay below)
to prevent false offhook indications, and that's most likely the
number you should be looking at. Am I anywhere close?

Here in the US a relevant spec is FCC part 68.312 (b) (1) (i), which says:

The dc resistance between tip and ring conductors, and between each of
the tip and ring conductors and earth ground SHALL be greater
than 5 MegaOhms for all dc voltages up to and including 100
volts.

That corresponds to a current of about 10 microamps.

Tim.
 
L

legg

Jan 1, 1970
0
Hi,

I'm trying to determine which Telcordia requirement document specifies
the allowable inrush current on -48V inputs of equipment.

I tried searching the Telcordia website without any luck. Can anyone
help?
I also tried asking in comp.dcom.telecom.tech and didn't get a single
reply.


BTW, other (non-US) specifications that I already have are ETSI EN 300
132-2 (applies in Europe) and Telstra 1555 (applies in Australia).

Thanks,
Allan.


GR-947-CORE
"Generic Requirements for a -48V Telecommunications Switchmode
Rectifier/Power Supply"
section3.3

Ten to six times the continuous input rating for rectifiers. But you
wanted downstream converters. I believe a tighter margin is required,
with an envelope of amplitude vs time being specified.

IEEE P1515-2000 - Recommended Practice for Electronic Power
Distribution Subsystems - defines test methods.

There have been applications where this has been specified by the end
user as less than double the continuous rating, in their purchase
specification.

Obviously, if it is a feature that turns out to have to be controlled
by extra circuitry, you might as well keep it as low as is practical.
There is usually no reason why it has to be larger than operating
values.

RL
 
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