Ceramic PTC thermistor for High Voltage Current Surge Protection

PTC Thermistor High Voltage Telecom Protect

PTC Thermistor High Voltage Telecom Protect

Ceramic positive temperature coefficient PTC thermistor help provide protection against power cross, power induction surges and lighting surge defined in ITU, Telcordia, UL. Available in chip, radial-leaded coated and non-coated configuration. This thermally sensitive semiconductor resistor provides reversible, self-resetting fuse protection against over-currents short circuit for telecommunication line protector units, improve the reliability of custom premises and network equipment.

PTC Thermistor Current Limiting Protection Device can be found providing resettable line protection at the exchange, monitoring hot spots and protecting ringers, battery feeds, transformers, switches and relay circuits. Also used extensively to protect the mobile phone’s battery pack against overcharging in land-based and radio mobile communications.

Advanced developments in telecom equipment in recent years have radically altered the protection requirements of both exchange and subscriber equipment. PTC Thermistor Current Protector must protect the telephone line circuit against overcurrent, which may be caused by the following examples:

  • Surges due to lighting strikes on or near to the line plant.
  • Short-term induction of alternating voltage from adjacent power lines or railway systems, usually caused when these lines or systems develop faults.
  • 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; However, even with primary line protection (usually a gas discharge tube), the PTC thermistor must fulfill severe requirements.

Surge pulses of upto 2KV 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 220V to 300V PTC thermistor is adequate. Without primary protection, 600V PTC device is necessary. We can manufacture a series of PTC thermistor fulfilling both requirements.

PTC Thermistor Replacement Idea for a Current Fuse

PTC thermistor Replacement Benefits

  • Automatic reset from protective trip up to 265V AC line contact
  • Compatible with the 600V over voltage test by UL60950
  • High resistance to the lighting surge  (A surge absorber is still required to protect SLIC)

 PTC Thermistor Application in Telecommunication Equipment

  • Central Office Switching Equipment (C.O): analog and digital line cards, POTS, T1/E1 equipment, xDSL modems and splitters, multiplexers, CSU/DSU, servers.
  • Primary Protection Modules: MDF (main distribution frame) modules, network interface devices (NIC).
  • Custom Premises Equipment, also known as subscriber terminal equipment (T.E.), IT equipment: Modem, phone sets, fax machines, phone wall outlet (plugs), alarm systems, answering machine, PBX systems, ADSL Splitters, internet appliance, POS terminals.
  • Access Network hardware, LAN WAN equipment, Powered Ethernet systems, VoIP (voice over IP equipment), integrated voice data (IVD), Set-top box (S.B), etc.
  • Landline telephones or FAX machines
  • Telephone interface of STB, VoIP equipment
  • Any other equipment of communication facility having a phone line interface

PTC Thermistors Telecom Application Features:

Compliant with ITU-T K20 K21 K45
–Basic level lightning surges (10/700μs)
–Basic level power Induction (600V,1A,0.2S)
–Power contact criteria A/B (230V,15min.)

Suitable for continuous connection to main voltage 110/230 VAC in tripped (high ohmic) condition.
Round leadless disk thermistor available for combined usage of PTC and primary protection, e.g gas arrestor.
Thermistor disk coated non-coated construction, diameter 5mm to 10mm.
Typical Resistance @25C (R25) 10 ohm, 12 ohm, 18 ohm, 20 ohm, 25 ohm, 50 ohm, 55 ohm.
Matching available with narrow resistance tolerance.
Tight resistance tolerance maintained after switching.
Negligible resistance drift after soldering or switching.

Telecom PTC Thermistor Performances

Rated zero-power Resistance(R25)
Operating temperature range: 25±2℃,  Within the allowable tolerance.
Non-operating characteristic
Operating temperature range: 40±2℃. In static air for 30min.
Max. voltage: 60VDC.  Non-operating current. Energized time: 60min.
(R-R25)/R25≤50%
Over-current operating characteristic
Operating temperature range: 25±2℃, Max. voltage of power supply: 220Vrms.
Test the time for the current decrease to limited value. See the spec. Table.
Over voltage withstanding (Power line contact)
Voltage of power supply: 250VAC, Initial current: 3A, Energized time: 30min .  Restore time in room temperature is 4 hours,  then test the R25. ΔR/R25≤20%.
Over current withstanding
Max. voltage of supply: 220VAC,  Initial current: 3A.  ON 60S, OFF 600S ,Cycle:30 times,   Restore time in room temperature is 4 hours,  then re-test the Rn.
ΔR/Rn≤20%.
Surge current withstanding
Current waves: 10/1000μS, Minimum opening circuit voltage: 1.0kv, Peak current: 25A, Interval: 3min, Cycle:30 times,                Restore time in room temperature is 4 hours, then re-test the R25.     ΔR/R25≤20%.
Induction voltage current withstanding (Only for maximum voltage more than 600V)
Max. voltage of supply: 650VAC,  Initial current: 1.1A., ON 60S, OFF 600S, Cycle:10 times,                                                                    Restore time in room temperature is 4 hours, then re-test the R25. ΔR/R25≤20%.
Fail Model
I. Voltage of power supply: 250VAC. Initial current: 10Arms,
II. Voltage of power supply: 600VAC. Initial current: 15Arms.
III. Voltage of power supply: 650VAC. Initial current: 10Arms.
Energized time: 30min. High resistance or open circuit is allowable. Low resistance state or firing is not allowed.
Restore time
The necessary time of a PTC to return to twice of R25. ≤60S.

Telecom PTC Thermistor Outline and Dimensions (unit:mm)

PTC Thermistors Drawing Chip Radial Part

PTC Thermistor for Telecom Line Card Protection Data

Part numberResistance
@25C
R25
(Ohm)
Non-trip current
Int
(mA)
Trip
current
@25C
It
(mA)
Tripping
time
@ max
current
(Seconds)
Max.
current
Imax
(A)
Max.
voltage
Vmax
(V)
Fail modelDimension
(mm)
 @25C @40C Dmax Tmax Φd
AMZ23-10RM13010 ohm130mA100mA260mA<0.2s 2.0A250V250V/10A 7.5 4.00.6
AMZ23-10RM15010 ohm150mA100mA260mA<0.3s 2.0A250V250V/10A 9.0 5.00.6
AMZ23-12RM13012 ohm130mA100mA260mA<0.3s 2.0A250V250V/10A 9.0 5.00.6
AMZ23-12RM09012 ohm90mA60mA160mA<0.2s 2.0A250V250V/10A 9.0 5.00.6
AMZ23-20RM10020 ohm100mA80mA200mA<0.2s 3.0A250V250V/10A 9.0 4.00.6
AMZ23-35RM09035 ohm90mA75mA180mA<0.2s 3.0A250V250V/5A 9.0 5.00.6
AMZ23-40RM08040 ohm80mA70mA160mA<0.2s 3.0A250V250V/5A 9.0 5.00.6
AMZ23-50RM07050 ohm70mA60mA150mA<0.2s 3.0A250V250V/5A 9.5 5.00.6
AMZ23-50RM07550 ohm75mA60mA150mA<0.2s 3.0A650V650V/10A 9.5 5.00.6
AMZ23-55RM07055 ohm70mA60mA150mA<0.2s 3.0A650V650V/10A 9.5 5.00.6
AMZ25-9RM1609 ohm160mA130mA330mA<0.8s 3.0A250V250V/10A 10.5 4.50.6
AMZ25-25RM10025 ohm100mA80mA220mA<0.2s 3.0A250V250V/10A 6.6 4.00.6
AMZ25-25RM12025 ohm120mA100mA300mA<0.4s 3.0A250V250V/10A 8.2 4.00.6
AMZ26-35RM080SMD35 ohm80mA60mA180mA<0.2s 2.5A250V250V/10A///

Note: Standard Resistance @25C (R25) allowable tolerance +/-20%, if not specified.

PTC Thermistor for Telecom MDF (Main Distribution Frame) Protection Data

Part numberResistance
@25C
R25(Ohm)
Non-trip
current
Int
(mA)
Trip
current
@25C
It
(mA)
Tripping
time
@ max
current
(Seconds)
Max.
current
Imax
(A)
Max.
voltage
Vmax
(V)
 Dimension
(mm)
@25C@40CDmaxTmaxΦd
AMZ21-10RM150 10 ohm150mA130mA350mA <4.0s 3A230V 7.2 1.5/
AMZ21-18RM110 18 ohm110mA90mA220mA <0.15s 3A250V 5.5 1.5/
AMZ21-18RM125 18 ohm125mA110mA250mA <0.18s 3A250V 5.5 2.0/
AMZ21-18RM130 18 ohm130mA110mA260mA <0.18s 3A250V 6.2 2.0/
AMZ21-18RM135 18 ohm135mA110mA270mA <0.2s 3A250V 6.6 2.0/
AMZ21-20RM085 20 ohm85mA70mA170mA <0.18s 3A250V 6.2 2.0/
AMZ21-25RM055 25 ohm55mA45mA110mA <0.4s 2A230V 5.3 2.0/
AMZ21-25RM060 25 ohm60mA50mA120mA <0.4s 2A230V 5.3 2.0/
AMZ21-25RM085 25 ohm85mA75mA170mA <0.7s 2A230V 5.3 2.0/
AMZ25-25RM055 25 ohm55mA45mA110mA <0.4s 1A230V 5.3 4.00.6
AMZ25-25RM060 25 ohm60mA50mA120mA <0.4s 1A230V 5.3 4.00.6
AMZ25-20RM145 20 ohm145mA100mA250mA <0.2s 3A250V 6.6 4.00.6
AMZ25-10RM130 10 ohm130mA110mA260mA <4.0s 1A230V 6.6 4.00.6
AMZ25-10RM150 10 ohm150mA135mA300mA <7.0s 1A230V 8.2 4.00.6
AMZ25-18RM125 18 ohm125mA110mA250mA <1.0s 1A230V 5.5 4.00.6
AMZ23-18RM135 18 ohm135mA110mA270mA <0.2s 3A250V 7.5 4.50.6
AMZ23-18RM110 18 ohm110mA90mA220mA <0.2s 3A250V 9.0 4.50.6
AMZ23-20RM100 20 ohm100mA80mA200mA <0.2s 3A250V 9.0 4.50.6
AMZ23-25RM085 25 ohm85mA75mA170mA <0.7s 1A230V 6.5 5.00.6
AMZ23-25RM090 25 ohm90mA70mA180mA <0.2s 3A250V 9.0 4.50.6

Note: Standard Resistance @25C (R25) allowable tolerance +/-20%, if not specified.

Circuit Examples of PTC thermistors for Telecom Protection

An example of PTC Thermistor for telecom circuit protection

An example of PTC Thermistor for telecom circuit protection

Telephone line PTC thermistors used for overcurrent protection

Telephone line PTC thermistors used for overcurrent protection

PTC Thermistor Telecom Application

PTC Thermistor Telecom Application

Consideration of Selecting PTC thermistor for Telecommunication Applications

Rated current and temperature

For most telecom applications the balance between the tip and ring (often referred to as longitudinal balance) is essential. A figure must be assigned to the balance between the line resistances that must apply initially and, after a short cooling period, after operation. Typically 1 Ω is demanded on delivery, which should also apply throughout the service life of a system. As opposed to PTC thermistor made of plastic materials, ceramic PTC thermistor always return to their initial resistance value, even after frequent heating/cooling cycles. The PTC thermistor is primarily used to protect the switching equipment against fault current through direct contact with a power line (power contact) or an induced surge of short duration and low voltage from a neighboring line (power induction). For obvious reasons, the rated current of the PTC thermistor should be kept as low as possible so that the protection responds quickly to overcurrents. The rated current should typically be slightly higher than the operating current of the system to be protected at the normal operating temperature. Here the dependence of the rated current on the temperature of the ambient must be considered.

Duration of disturbance — voltage classes

An aspect that is too often neglected is the duration of the power contact. Such disturbances can go undetected for many hours, meaning that the PTC thermistor could be held in the high resistance condition exposed to the line voltage for an indefinite period. AMWEI PTC thermistors for telecommunication applications have a maximum switching voltage of at least 265 V AC and can withstand this condition indefinitely.

Imbalance on the line — resistance of PTC thermistor

For most telecom applications the balance between the tip and ring (often referred to as longitudinal balance) is essential. A figure must be assigned to the balance between the line resistances that must apply initially and, after a short cooling period, after operation. Typically 1 Ω is demanded on delivery, which should also apply throughout the service life of a system. As opposed to PTC thermistor made of plastic materials, ceramic PTC thermistor always return to their initial resistance value, even after frequent heating/cooling cycles.

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