Transcript Product Training

Bourns® Telefuse™
The latest addition
to the Bourns®
Circuit Protection product offering
1
Introduction
Series
Description
B1250T
Telecom line fuse
Device Symbol
Part Photo
Applications
Ampere
rating
Voltage
Rating
Line Card
1.25 A
600 V
Peak Surge
current
10/1000
100
500 mA
600 V
25
CPE
B0500T
Telecom line fuse
Bourns® Telefuse™
•Part numbers: B1250T and B0500T
1.25 version most popular
•10mm SMD body
•Overcurrent protection compliance to:
UL 60950 - CPE equipment
Telcordia GR-1089 - Central Office equipment
•Safely interrupts 600V/60A powercross
•Withstands lightning surge without opening
2
Telecom Fuse Applications
The fuse is used as secondary overcurrent protection in
central office and customer premises applications.
The fuse is nearly always used in conjunction with a
thyristor-based overvoltage protector (Bourns TISP
product).
There are three design paths that a customer may take
for building their overcurrent protection block.
The goal of all options is to function properly after
“first level” tests and fail safely during “second level”
tests.
3
Path One - Use of a PTC
A PTC gives a resettable solution, but the PTC has
inherent properties of 8-10Ω resistance and an
unpredictable resistance hyterisis as a result of
overcurrent event.
These properties may not be allowed in the functionality
of the design.
The PTC is the right product to use if resettability is a
critical feature of the system.
4
Path Two - Use of Line Feed Resistors (LFR)
An LFR offers very stable current limiting and very tight
matching between tip and ring pair, even after an
overcurrent event.
LFRs are very robust and can dissipate a lot of energy,
but are also physically large.
Many applications demand minimal resistance, and the
LFR can realistically achieve only a minimum of around
4Ω and still meet GR1089 requirements.
Some applications (POTS cards) require a higher
resistance of >30Ω, so the LPM is the right choice.
5
Path Three - Telecom Fuses
The fuse provides a no-resistance overcurrent protection.
This solution can be used in most all of the telecom circuit
protection applications, especially xDSL and T1-E1.
This is a distinct advantage, as the resistance of the PTC
and LPM preclude them from being used.
With the development of 100A thyristor overvoltage
protectors, a customer can eliminate the LFR which was
needed in the past to protect the thyristor limited to 50A.
6
Applications
Telefuse used here
7
The End
… thank you
8