Circuit & System Protection


Gated unidirectional overvoltage and overcurrent protector

12 July 2006 Circuit & System Protection

Bourns' TISP8250 is a telecommunications protector, designed for use in a variety of applications including: telephone handset/base station and SLIC protection in access or telecommunication centre equipment.

This unidirectional protector is intended for use with diode bridge-fed circuits, like those commonly employed in analog telephone handsets and DECT base stations, or in protection schemes where reverse biased conditions will not occur. The TISP8250 can be used as a fixed overvoltage protector having a 'natural' maximum breakover voltage of 340 V - alternatively, when used with an external reference such as a zener diode, it can be made to operate as a gate triggered protector.

The device can also be used as a current-triggered protector. Such an application would use the TISP8250 as a conventional crowbar across the circuit to be protected. Triggering would be caused by a sense resistor in series with the circuit to be protected connected to the TISP8250 gate and cathode terminals. In this arrangement, the initial fault current flowing into the circuit under protection (CUP) will cause sufficient voltage drop across the sense resistor to trigger the protector. The sense resistor value must allow for all normal CUP operating conditions, and yet cause the TISP8250 to trigger under fault conditions. When triggered, the TISP8250 shunts the main fault current around the input circuit diverting the fault current away from the CUP which must be capable of handling the initial fault condition prior to protector triggering.

For fixed voltage operation (no external trigger) the TISP8250 behaves like a conventional fixed-voltage protector. The breakover current (I(BO) 200 mA maximum @ 25°C) and holding current values make the TISP8250 suitable for the protection of conventional POTS line equipment, when operated with associated fault current limiting devices, such as Bourns Multifuse products and Bourns Line Protection Modules.



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