APPLICATION NOTE
AN574/1197
TRANSIL/TRISIL COMPARISON

A. Bremond
1. INTRODUCTION
R
S
P
OVER-
-VOLTAGE
SOURCE
DEVICE
TO BE
PROTECTED
Figure1A : Classical schematic of parallel protection
To protect a sensitive device there are two
different approaches.
The first one is to use series protectors, the
second one parallel suppressors. The
technologies used in both cases are such
that the series devices are suitable for long
duration surges, while parallel protectors are
very efficient for the high current short
duration stresses which represent the great
majority of cases.
For the parallel protection solutions, two
philosophies can be used. The first one is
represented by a breakdown based device
and the second one by a breakover based
protector, respectively known as the Transil
and the Trisil.
Figure 1B : Electrical characteristics
2. TRANSIL / TRISIL COMPARISON
2.1. Electrical characteristics
I
V
-V
BR
V
BR
TRANSIL I
V
-V
BO
V
BO
TRISIL
The Transil is a clamping device which
suppresses all overvoltages above the
breakdown voltage (V
BR
)
The Trisil is a crowbar device which switches on
when overvoltages rise up to the breakover
voltage (± VBO).
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