2322 66. 9....
PTC Thermistors, Overload Protection
For Telecommunication
Vishay BCcomponents
inrush power at normal mains voltage. Under such
conditions, overload currents of up to 10 A on a 230 V mains
could occur for up to several hours. To handle this power, the
resistance/temperature characteristic of the thermistor must
have a very steep slope and the ceramic must be extremely
homogeneous.
OVERCURRENT PROTECTION OF
TELECOMMUNICATION LINES
The PTC thermistor must protect the telephone line circuit
against overcurrent which may be caused by the following
examples:
• Surges due to lightning strikes on or near to the line plant.
In case of overcurrent due to short-term induction of
alternating voltages, currents of several AMPs with voltages
as high as 650 VRMS can be present for several seconds
• Short-term induction of alternating voltages from adjacent
power lines or railway systems, usually caused when these
lines or systems develop faults.
For standard high voltage applications, resistance values
from 25 to 50 Ω are available. However, ISDN networks
which carry high-frequency sound and vision, need lower line
impedance.
• Direct contact between telephone lines and power lines.
To provide good protection under such conditions a PTC
thermistor is connected in series with each line, usually as
secondary protection; see Typical Telephone Line drawing
on page 1. However, even with primary line protection
(usually a gas discharge tube), the PTC thermistor must fulfil
severe requirements.
Telecommunication designers are therefore demanding high
voltage thermistors with much lower R25 values, which
places even greater demands on the manufacture of PTC
thermistors. For these applications PTC thermistors which
Surge pulses of up to 2 kV can occur and in order to
withstand short-term power induction the PTC thermistor
must withstand high voltages. If the line has primary
protection a 220 V to 300 V PTC thermistor is adequate.
Without primary protection, however, a 600 V PTC device is
necessary. Vishay BCcomponents manufacturers a range of
PTC thermistors (see Electrical Data and Ordering
Information Table ) covering both requirements.
have
a
R25 value of 10 Ω with voltages in the
300 to 600 VRMS range are available.
In a typical telephone line application, two PTC thermistors
are used, one each for the tip and ring (or A and B) wire
together with their series resistors. For good line balance it is
important that the thermistor and resistor pairs are matched.
On request, Vishay BCcomponents can supply matched or
binned PTC thermistors with R25 values matched to as close
as 0.5 Ω.
In the case of direct contact between the telephone line and
a power line, the PTC thermistor must withstand very high
DIMENSIONS in millimeters
T
T
D
D
COMPONENT OUTLINE
H
3
H
L
2
For dimensions see Specific Physical
Dimentions and Packaging table.
F
1
Lead pitch F = 5 mm +0.6/-0.1.
d
Lead thickness d = 0.6 mm 10%.
CCB914
SPECIFIC PHYSICAL DIMENSIONS AND PACKAGING in millimeters
CATALOG
NUMBER
2322 ... .....
D
MAX.
T
H3
MAX.
PACKAGING(1)(2)
H2
L1
MAX.
7.0
8.5
7.0
6.7
7.0
8.3
6.8
11
4.0
5.0
4.0
4.0
5.0
4.0
4.3
4.5
4.5
1.8
4.0
6.0
5.0
3.5 ±0.5
1.5 to 3.0
2.0 ±0.5
1.5 to 3.0
1.5 to 3
1.5 to 3.0
1.5 to 3.0
4.0 ±1.0
4.0 ±1.0
−
−
−
−
−
−
−
−
−
11.0
11.5
9.8
10.0
10.0
11.0
10.1
15.5
15.5
−
taped H0 = 16 mm
taped H0 = 16 mm
taped H0 = 18 mm
taped H0 = 18 mm
taped H0 = 16 mm
taped H0 = 18 mm
taped H0 = 16 mm
taped H0 = 16 mm
taped H0 = 16 mm
disc on tray
661 91066
661 93048
661 93147
661 93025
661 93037
661 93175(3)
661 93142
662 93081
662 93074(3)
661 93118
661 93148
663 93025(3)
661 93078
11
−
−
−
6.7
7.0
13.6
8.3
2.0 ±0.5
4.0 ±1.0
1.5 ±0.5
9.8
18.6
10.3
taped H0 = 18 mm
bulk
20 ±4.0
20 ±3.0
bulk
www.vishay.com
164
For technical questions contact: nlr.europe@vishay.com
Document Number: 29070
Revision: 10-Oct-03
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