On 9/17/2008, Daniel Roman wrote:
If youve been subjected to the current limiting requirement from the
CTI
spec, what is the feed resistance that India uses? The spec does not give any
details. Is it the same as the old CTR21 for France, is it 600 ohms,
something else?
Hi Dan:
I have a copy of IR/TEL-01/03.JAN2003, which may or may not be the current
version. In clause 2.5, they list the feed characteristics of eight different
central office switches that are used in India. For the 60 mA limiting
feature in the TE, it appears that the worst case feed is a NEAX 61E switch,
with 58 volts applied through 400 ohms.
By my calculations, the power dissipated in the TE at 60 mA would be 1.98
watts with this feed circuit. With the TBR 21 feed circuit (50 volts, 300
ohms), the power is 1.92 watts.
So, if India uses the worst-case feed voltage of 57 volts, the power
dissipation in the TE will be about the same as with TBR 21. However, if
India uses the nominal voltage of 48 volts, the power dissipation in the TE
drops to 1.4 watts. This is not much worse than what you can get even without
current limiting in the TE.
Joe Randolph
Telecom Design Consultant
Randolph Telecom, Inc.
781-721-2848 (USA)
[email protected]
http://www.randolph-telecom.com <http://www.randolph-telecom.com/>
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