PTC Thermistor Current Protect Resettable Fuse

What is PTC Thermistors Current Protector Resettable Fuse?

PTC Thermistor Current Protection Resettable Fuse

PTC Thermistor Current Protection Resettable Fuse

PTC Thermistor Current Protector Resettable Fuse are ceramic-based doped barium titanate PTC thermistors discs, in through-hole rugged design, used instead of conventional fuses to protect load, such as transformers, instruments,  power supply, or electronic circuit, against overcurrent overload and short circuit,  for circuit protection inrush current limit function, by utilizing ceramic PTC thermistors thermal property that resistance increases sharply at Curie Temperature (also called Switch Temperature, Reference Temperature), reduces the current flow to the load to an admissible low level.

PTC thermistors protector not only respond to inadmissibly high currents but also if a preset temperature limit is exceeded.

PTC thermistor over-current protector limits the power dissipation of the whole circuit by increasing their resistance and thus reducing the current to a harmless residual value.

In contrast to conventional fuses, PTC thermistor resettable fuses do not have to be replaced after elimination of the fault but resume their protective function immediately after a short cooling-down time.

PTC Thermistor Resistance Change with Current Graph

PTC Thermistor Resistance Change with Current Graph

PTC Thermistor Trip Time vs. Current Chart

PTC Thermistor Trip Time vs. Current Chart

PTC Thermistor as Current Protect Resettable Fuse

PTC Thermistor as Current Protect Resettable Fuse

PTC Thermistors Circuit Over-current Overload Protection Application

Simplest circuit for PTC Thermistor protecting a transformer

Simplest circuit for PTC Thermistor protecting a transformer

Positive Temperature Coefficient PTC thermistor applies in the over-current overload and short circuit protection of transformers, battery charger, switches, switch power supply, adaptor, meter, instrumentation, apparatus, electronic coils, control panels, air conditioner, automotive electron, etc.

How PTC Thermistor Resettable Fuse Protect Circuit Against Overload Over-current Work? Operating Principle

PTC Thermistor Protective Threshold Current Graph

PTC Thermistor Protective Threshold Current Graph

PTC thermistor Resettable Fuse Circuit Protection operating principle is as indicated in the following.

When a circuit is in the normal status, the current through PTC is lower than the rated current and PTC thermistors protector is in the normal state with small resistance value, which will not affect the normal operation of the protected circuit.

In case of some fault in the circuit and the current is greater than the rated current, the PTC thermistor protector will become hot quickly and present a high resistance state, which sets the circuit relatively “off” to protect the circuit from damage.

After the fault is removed, PTC thermistor protector will automatically restore its low resistance state and the circuit will resume normal operation.

Normally, when PTC thermistor is used as an overcurrent protection component, it is preferred to select maximum operating current, maximum operating voltage and proper specifications.

Furthermore such factors should be taken into consideration as the dimensions of the components, rated zero-power resistance, operating temperature range, etc.

Different Curie Temperature PTC Non-trip Current vs. Ambient Temperature Graph

Different Curie Temperature PTC Non-trip Current vs. Ambient Temperature Graph

Relation between operating temperature, operating current and non-operating current is as shown in following Figure. Operating current is normally 2~3 times non-operating current, and both of the currents will be reduced as operating temperature increases.

When connected in series with the input of an electrical or electronic circuit, such as a small motor or power supply, the PTC thermistor acts as a self-resettable fuse, protecting the circuit against current, voltage and temperature overload conditions.

In normal operating conditions the PTC thermistor resistance is low , and the current is below its hold value (Ihold). However, an overload will quickly heat up the PTC thermistor until, at around switch temperature (Ts), its resistance becomes high, limiting the current to far below its trip value (Itrip), and so protecting the circuit.

Operating of PTC Thermistor as Current Protect Resettable Fuse

Operating of PTC Thermistor as Current Protect Resettable Fuse

PTC Thermistor Replacement Idea for a Resistor and Fuse Solution

PTC Thermistor Replacement idea for a resistor and fuse solution

Benefits

  • Protection against overcurrent situations
  • Automatic reset from protective trip mode
  • Space-saving
  • Various characteristics to meet a suitable resistance value

3 types over-current and overload protection PTC thermistor circuit protector carries

PTC Thermistors for over-current overload protection

PTC Thermistors for over-current overload protection

PTC thermistor for current overload protection(Fig. 4):RL1 is the loading current in normal operating state, When overloading resistance decreases, such as transformer short circuit, loading curve changes from RL1to RL2 , exceeding point B, PTC thermistor protector will enter into protection state.

PTC thermistor for voltage overload protection (Fig. 5): Power voltage increases, such as increases abruptly from 220V to 380V, loading curve changes from RL1to RL2 , exceeding point B, PTC thermistor protector will enter into protection state.

More detailed information on AMWEI PTC thermistor for high voltage current surge telecom protection can be founded .

PTC thermistor for temperature protection(Fig. 6): When ambient temperature increases exceeding certain temperature, PTC thermistor voltage-resistance curve changes from A-B-E to A-B1-F, loading curve RL , exceeding point B1PTC thermistor protector will enter into protection state. More detailed information on  AMWEI PTC thermistor for temperature protection can be founded in PTC Thermistors Limit Temperature Sensor Temperature Protection Page.

Electrical Characteristics Imax as a Function of Voltage Graph

Electrical Characteristics Imax as a Function of Voltage Graph

Current Deviation as a Function of Ambient Temperature Chart

Current Deviation as a Function of Ambient Temperature Chart

Voltage Derating as a Function of Ambient Temperature Graph

Voltage Derating as a Function of Ambient Temperature Graph

Circuit protection diagram examples using PTC thermistor over-current protection devices

PTC Thermistor Current Protector Application Diagram Examples

PTC Thermistor Current Protector Application Diagram Examples

PTC Thermistor Current Protector Transformer Primary or Secondary Protection Diagram

PTC Thermistor Current Protector Transformer Primary or Secondary Protection Diagram

PTC Thermistor for inrush current limit circuit diagram

PTC Thermistor for inrush current limit circuit diagram

Current Protection PTC Thermistor Engineering Drawing

Current Protection PTC Thermistor Outlook Engineering Drawing

Current Protection PTC Thermistor Outlook Engineering Drawing

AMWEI PTC Thermistor Current Protect Fuse 265V/250V Series Data

AMWEI Part Number Resistance
at 25C
(R25)
(Ohm)
Non-trip
Current
Int(mA)
Trip Current
@25C
It
(mA)
Max.
Voltage
Vmax
(V)
Max.
Current
Imax
(A)
 Reference
Temp
Tref
Dimension
(mm)
 @25C  @60C  Dmax  Tmax  Φd
AMZ11-20P2R6H265 2.6 ohm  650mA  500mA 1300mA 265V 4.3A 120C 22.0 5.0 0.6
AMZ11-20P3R7H265 3.7 ohm 530mA 430mA 1050mA 265V 4.3A 120C 22.0 5.0 0.6
AMZ11-20P5RH265 5.0 ohm 480mA 370mA 970mA 265V 4.3A 120C 22.0 5.0 0.6
AMZ11-16P5RH265 5.0 ohm 420mA 320mA 840mA 265V 3.1A 120C 17.5 5.0 0.6
AMZ11-16P6RH265 6.0 ohm 390mA 300mA 780mA 265V 3.1A 120C 17.5 5.0 0.6
AMZ11-16P7RH265 7.0 ohm 350mA 280mA 700mA 265V 3.1A 120C 17.5 5.0 0.6
AMZ11-13P10RH265 10 ohm 260mA 200mA 520mA 265V 1.8A 120C 14.0 5.0 0.6
AMZ11-13P12RH265 12 ohm 225mA 180mA 450mA 265V 1.8A 120C 14.0 5.0 0.6
AMZ11-13P50RH265 50 ohm 130mA 100mA 260mA 265V 1.8A 120C 14.0 5.0 0.6
AMZ11-12P7RH265 7 ohm 320mA 250mA 640mA 265V 1.8A 120C 14.0 5.5 0.6
AMZ11-12P8RH265 8 ohm 300mA 230mA 600mA 265V 1.8A 120C 14.0 5.5 0.6
AMZ11-12P9RH265 9 ohm 290mA 220mA 580mA 265V 1.8A 120C 14.0 5.5 0.6
AMZ11-12P10RH265 10 ohm 250mA 200mA 500mA 265V 1.8A 120C 14.0 5.5 0.6
AMZ11-12P12RH265 12 ohm 240mA 180mA 480mA 265V 1.8A 120C 14.0 5.5 0.6
AMZ11-12P15RH265 15 ohm 200mA 160mA 400mA 265V 1.8A 120C 14.0 5.5 0.6
AMZ11-12P27RH270 27 ohm 120mA 90mA 350mA 270V 1.8A 120C 14.0 5.5 0.6
AMZ11-12P101H265 100 ohm 50mA 40mA 100mA 265V 1.8A 120C 14.0 5.5 0.6
AMZ11-10P12RH265 12 ohm 230mA 160mA 460mA 265V 1.2A 120C 11.5 5.0 0.6
AMZ11-10P15RH265 15 ohm 180mA 140mA 350mA 265V 1.2A 120C 11.5 5.0 0.6
AMZ11-10P18RH265 18 ohm 170mA 130mA 340mA 265V 1.2A 120C 11.5 5.0 0.6
AMZ11-10P39RH265 39 ohm 130mA 100mA 250mA 265V 1.2A 120C 11.5 5.0 0.6
AMZ11-08P15RH250 15 ohm 150mA 120mA 300mA 250V 0.8A 120C 9.5 5.0 0.6
AMZ11-08P22RH250 22 ohm 135mA 110mA 270mA 250V 0.8A 120C 9.5 5.0 0.6
AMZ11-08P25RH265 25 ohm 130mA 100mA 250mA 265V 0.8A 120C 9.5 5.0 0.6
AMZ11-08P35RH265 35 ohm 115mA 90mA 225mA 265V 0.8A 120C 9.5 5.0 0.6
AMZ11-08P39RH270 39 ohm 105mA 70mA 210mA 270V 0.8A 120C 9.5 5.0 0.6
AMZ11-08P45RH265 45 ohm 105mA 80mA 200mA 265V 0.8A 120C 9.5 5.0 0.6
AMZ11-08P55RH265 55 ohm 90mA 70mA 180mA 265V 0.8A 120C 9.5 5.0 0.6
AMZ11-08P70RH265 70 ohm 75mA 60mA 150mA 265V 0.8A 120C 9.5 5.0 0.6
AMZ11-07P82RH265 82 ohm 70mA 50mA 140mA 265V 0.6A 120C 8.5 5.0 0.6
AMZ11-07P56RH265 56 ohm 90mA 60mA 175mA 265V 0.6A 120C 8.5 5.0 0.6
AMZ11-06P33RH250 33 ohm 110mA 85mA 200mA 250V 0.4A 120C 7.5 4.5 0.6
AMZ11-05P70RH265 70 ohm 65mA 50mA 130mA 265V 0.3A 120C 6.5 5.0 0.6
AMZ11-05P85RH265 85 ohm 60mA 45mA 120mA 265V 0.3A 120C 6.5 5.0 0.6
AMZ11-05P121H265 120 ohm 45mA 35mA 90mA 265V 0.3A 120C 6.5 5.0 0.6
AMZ11-05P181H265 180 ohm 40mA 30mA 80mA 265V 0.3A 120C 6.5 5.0 0.6
AMZ11-04P70RH250 70 ohm 50mA 40mA 100mA 250V 0.2A 120C 5.5 5.0 0.6
AMZ11-04P121H265 120 ohm 40mA 30mA 80mA 265V 0.2A 120C 5.5 5.0 0.6
AMZ11-03P151H250 150 ohm 40mA 30mA 75mA 250V 0.2A 120C 4.5 5.0 0.5
AMZ11-03P221H265 220 ohm 30mA 24mA 60mA 265V 0.2A 120C 4.5 5.0 0.5
AMZ11-12N12RH265 12 ohm 200mA 140mA 400mA 265V 1.8A 100C 14.0 5.0 0.6
AMZ11-12N10RH265 10 ohm 220mA 180mA 440mA 265V 1.8A 100C 14.0 5.0 0.6
AMZ11-12N8RH265 8 ohm 250mA 200mA 500mA 265V 1.8A 100C 14.0 5.0 0.6
AMZ11-10N12RH250 12 ohm 180mA 130mA 350mA 250V 1.2A 100C 11.5 5.0 0.6
AMZ11-10N12RH265 12 ohm 210mA 160mA 420mA 265V 1.2A 100C 12.0 5.0 0.6
AMZ11-10N15RH265 15 ohm 175mA 120mA 320mA 265V 1.2A 100C 11.5 5.0 0.6
AMZ11-10N18RH265 18 ohm 145mA 110mA 320mA 265V 1.2A 100C 11.5 5.0 0.6
AMZ11-10N22RH265 22 ohm 140mA 100mA 260mA 265V 1.2A 100C 11.5 5.0 0.6
AMZ11-10N27RH265 27 ohm 120mA 90mA 240mA 265V 1.2A 100C 11.5 5.0 0.6
AMZ11-08N25RH265 25 ohm 110mA 80mA 230mA 265V 1.0A 100C 9.5 5.0 0.6
AMZ11-08N35RH265 35 ohm 95mA 70mA 190mA 265V 1.0A 100C 9.5 5.0 0.6
AMZ11-08N45RH265 45 ohm 85mA 55mA 170mA 265V 1.0A 100C 9.5 5.0 0.6
AMZ11-07N22RH250 22 ohm 120mA 80mA 210mA 250V 0.5A 100C 8.5 5.0 0.6
AMZ11-07N35RH265 35 ohm 95mA 70mA 190mA 265V 0.5A 100C 8.5 5.0 0.6
AMZ11-07N50RH265 50 ohm 85mA 60mA 170mA 265V 0.5A 100C 8.5 5.0 0.6
AMZ11-07N60RH265 60 ohm 80mA 50mA 160mA 265V 0.5A 100C 8.5 5.0 0.6
AMZ11-05N82RH265 82 ohm 55mA 40mA 105mA 265V 0.3A 100C 6.5 5.0 0.6
AMZ11-05N101H265 100 ohm 50mA 35mA 100mA 265V 0.3A 100C 6.5 5.0 0.6
AMZ11-05N121H265 120 ohm 45mA 32mA 90mA 265V 0.3A 100C 6.5 5.0 0.6
AMZ11-05N151H265 150 ohm 38mA 30mA 80mA 265V 0.3A 100C 6.5 5.0 0.6
AMZ11-05N201H265 200 ohm 30mA 25mA 65mA 265V 0.3A 100C 6.5 5.0 0.6
AMZ11-05N301H265 300 ohm 27mA 20mA 55mA 265V 0.3A 100C 6.5 5.0 0.6
AMZ11-05N601H265 600 ohm 20mA 12mA 40mA 265V 0.2A 100C 6.5 5.0 0.6
AMZ11-04N151H265 150 ohm 36mA 28mA 80mA 265V 0.3A 100C 5.5 5.0 0.6
AMZ11-03N151H265 150 ohm 33mA 25mA 65mA 265V 0.2A 100C 4.5 5.0 0.5
AMZ11-03N101H250 100 ohm 40mA 30mA 80mA 250V 0.2A 100C 4.5 5.0 0.5
AMZ11-03N70RH250 70 ohm 45mA 35mA 90mA 250V 0.1A 100C 4.5 5.0 0.5
AMZ11-08M25RH265 25 ohm 90mA 50mA 180mA 265V 0.8A 80C 9.5 5.0 0.6
AMZ11-08M35RH265 35 ohm 80mA 45mA 160mA 265V 0.8A 80C 9.5 5.0 0.6
AMZ11-08M40RH265 40 ohm 75mA 40mA 150mA 265V 0.8A 80C 9.5 5.0 0.6
AMZ11-08M50RH265 50 ohm 60mA 35mA 120mA 265V 0.8A 80C 9.5 5.0 0.6
AMZ11-07M101H265 100 ohm 40mA 25mA 80mA 265V 0.6A 80C 8.5 5.0 0.6
AMZ11-05M70RH250 70 ohm 50mA 30mA 100mA 250V 0.3A 80C 6.5 5.0 0.6
AMZ11-05M121H265 120 ohm 30mA 20mA 60mA 265V 0.3A 80C 6.5 5.0 0.6
AMZ11-03M101H250 100 ohm 25mA 18mA 55mA 250V 0.2A 80C 4.5 5.0 0.5
AMZ11-03M151H265 150 ohm 22mA 15mA 45mA 265V 0.2A 80C 4.5 5.0 0.5

AMWEI PTC Thermistor Current Protect Fuse 140V Series Data

AMWEI Part Number Resistance
@25C
 (R25)
(Ohm)
Non-trip
Current
Int(mA)
Trip Current
@25C
It
(mA)
Max.
Voltage
Vmax
(V)
Max.
Current
Imax
(A)
 Reference
Temp
Tref
Dimension
(mm)
 @25C  @60C  Dmax  Tmax  Φd
 AMZ12-20P1R5H140 1.5 ohm  850mA  680mA 1700mA 140V 4.3A 120C 22.0 5.0 0.6
AMZ12-20P2R6H140 2.6 ohm 650mA 500mA 1300mA 140V 4.3A 120C 22.0 5.0 0.6
AMZ12-16P4R7H140 4.7 ohm 425mA 330mA 850mA 140V 3.1A 120C 17.5 5.0 0.6
AMZ12-16P5R6H140 5.6 ohm 400mA 310mA 800mA 140V 3.1A 120C 17.5 5.0 0.6
AMZ12-13P6R8H140 6.8 ohm 325mA 250mA 650mA 140V 1.8A 120C 14.0 5.0 0.6
AMZ12-12P5R6H140 5.6 ohm 325mA 250mA 650mA 140V 1.8A 120C 13.5 5.0 0.6
AMZ12-12P6R8H140 6.8 ohm 300mA 230mA 600mA 140V 1.8A 120C 13.5 5.0 0.6
AMZ12-10P10RH140 10 ohm 225mA 170mA 450mA 140V 1.2A 120C 11.5 5.0 0.6
AMZ12-10P6R8H140 6.8 ohm 275mA 200mA 550mA 140V 1.2A 120C 11.5 5.0 0.6
AMZ12-08P22RH140 22 ohm 135mA 110mA 270mA 140V 0.8A 120C 9.5 5.0 0.6
AMZ12-06P25RH140 25 ohm 125mA 90mA 250mA 140V 0.5A 120C 7.0 5.0 0.6
AMZ12-16R2RIH140 2.1 ohm 710mA 570mA 1420mA 140V 3.1A 140C 17.5 5.0 0.6
AMZ12-13R3R8H140 3.8 ohm 500mA 400mA 1000mA 140V 1.8A 140C 14.5 5.0 0.6
AMZ12-10R15RH140 15 ohm 210mA 170mA 420mA 140V 1.2A 140C 11.5 5.0 0.6
AMZ12-10R6R7H140 6.7 ohm 300mA 230mA 600mA 140V 1.2A 140C 11.5 5.0 0.6
AMZ12-10R10RH140 10 ohm 250mA 200mA 500mA 140V 1.2A 140C 11.5 5.0 0.6
AMZ12-08R12RH140 12 ohm 200mA 160mA 400mA 140V 0.6A 140C 9.5 5.0 0.6

AMWEI PTC Thermistor Current Protect Fuse 60V Series Data

AMWEI Part Number Resistance
@25C
(R25)
(Ohm)
Non-trip
Current
Int(mA)
Trip Current
@25C
It
(mA)
Max.
Voltage
Vmax
(V)
Max.
Current
Imax
(A)
 Reference
Temp
Tref
Dimension
(mm)
 @25C  @60C  Dmax  Tmax  Φd
AMZ13-16P2R3H60 2.3 ohm  550mA  450mA  1100mA 60V 8.0A 120C 17.5 4.0 0.6
AMZ13-12P3R7H60 3.7 ohm 380mA 320mA 750mA 60V 5.5A 13.5 4.0 0.6
AMZ13-10P5R6H60 5.6 ohm 300mA 250mA 600mA 60V 4.3A 11.0 4.0 0.6
AMZ13-08P9R4H60 9.4 ohm 180mA 150mA 360mA 60V 3.0A 9.0 4.0 0.6
AMZ13-05P25RH60 25 ohm 100mA 85mA 200mA 60V 1.0A 6.5 4.0 0.6
AMZ13-03P55RH60 55 ohm 60mA 50mA 120mA 60V 0.7A 4.5 4.0 0.5
AMZ13-08M4R7H60 4.7 ohm 180mA 120mA 360mA 60V 3.0A 80C 9.0 4.0 0.6

AMWEI PTC thermistor Current Limiting Devices for Transformer Over-current Overload Protection 265V, 100C
(For application of PTC thermistor protector installation inside transformer windings coil)

AMWEI Part Number Resistance
@25C
(R25)
(Ohm)
Non-trip
Current
Int(mA)
Trip Current
@25C
It
(mA)
Max.
Voltage
Vmax
(V)
Max.
Current
Imax
(A)
 Reference
Temp
Tref
Dimension
(mm)
 @25C  @80C  Dmax  Tmax  Φd
AMZ11-05N121H265 120 ohm 45mA 25mA 90mA 265V 0.4A 100C 6.5 5.0 0.6
AMZ11-05N151H265 150 ohm 38mA 20mA 80mA 265V 0.4A 6.5 5.0 0.6
AMZ11-07N22RH265 22 ohm 110mA 60mA 220mA 265V 0.7A 8.0 4.5 0.6
AMZ11-07N32RH265 32 ohm 95mA 50mA 190mA 265V 0.7A 8.0 4.5 0.6
AMZ11-07N55RH265 55 ohm 70mA 40mA 140mA 265V 0.7A 8.0 5.0 0.6
AMZ11-08N30RH265 30 ohm 100mA 55mA 200mA 265V 1.0A 9.0 5.0 0.6
AMZ11-08N35RH265 35 ohm 90mA 50mA 180mA 265V 1.0A 9.0 5.0 0.6
AMZ11-08N40RH265 40 ohm 85mA 45mA 170mA 265V 1.0A 9.0 5.0 0.6
AMZ11-08N39RH265 39 ohm 95mA 50mA 180mA 265V 1.2A 9.5 5.0 0.6
AMZ11-08N25RH265 25 ohm 110mA 60mA 220mA 265V 1.2A 9.5 5.0 0.6
AMZ11-10N22RH265 22 ohm 125mA 70mA 250mA 265V 1.5A 11.0 5.0 0.6
AMZ11-10N18RH265 18 ohm 145mA 80mA 290mA 265V 1.5A 11.0 5.0 0.6
AMZ11-10N12RH265 12 ohm 170mA 95mA 340mA 265V 1.5A 11.0 5.0 0.6
AMZ11-12N18RH265 18 ohm 180mA 100mA 360mA 265V 2.0A 13.5 5.0 0.6
AMZ11-12N12RH265 12 ohm 210mA 120mA 420mA 265V 2.0A 13.5 5.0 0.6

Note: If not specified, Resistance @25C (R25) tolerance shall be +/-25%.

AMWEI PTC Thermistor Current Limiting Devices for Transformer over-current Overload Protection 265V 120C
(For application of PTC thermistor protector installation outside transformer windings coil)

AMWEI Part Number Resistance @25C
(R25)
(Ohm)
Non-trip
Current
Int(mA)
Trip Current
@25C
It
(mA)
Max.
Voltage
Vmax
(V)
Max.
Current
Imax
(A)
 Reference
Temp
Tref
Dimension
(mm)
 @25C  @60C  Dmax  Tmax  Φd
AMZ11-16P6R0H265 6.0 ohm 390mA 300mA 780mA 265V 3.1A 120C 17.5 5.0 0.6
AMZ11-13P10RH265 10 ohm 260mA 200mA 520mA 265V 1.8A 14.0 5.0 0.6
AMZ11-12P10RH265 10 ohm 250mA 200mA 500mA 265V 1.8A 13.5 5.0 0.6
AMZ11-10P15RH265 15 ohm 180mA 140mA 350mA 265V 1.2A 11.0 5.0 0.6
AMZ11-08P25RH265 25 ohm 130mA 100mA 250mA 265V 0.8A 9.0 5.0 0.6
AMZ11-08P35RH265 35 ohm 115mA 90mA 225mA 265V 0.8A 9.0 5.0 0.6
AMZ11-08P45RH265 45 ohm 105mA 80mA 200mA 265V 0.8A 9.0 5.0 0.6
AMZ11-08P55RH265 55 ohm 90mA 70mA 180mA 265V 0.8A 9.0 5.0 0.6
AMZ11-05P70RH265 70 ohm 65mA 50mA 130mA 265V 0.3A 6.5 5.0 0.6
AMZ11-03P151H250 150 ohm 40mA 30mA 75mA 250V 0.2A 4.5 5.0 0.5

Note: If not specified, Resistance @25C (R25) tolerance shall be +/-25%.

AMWEI PTC thermistor current limiting devices for measuring instrumentation and meter circuit overload and short circuit protection, Voltage 265V/420V/550V, Reference Temperature 80C, 100C, 120C

AMWEI Part Number Resistance @25C
(R25)
(Ohm)
Non-trip
Current
Int(mA)
Trip Current
@25C
It
(mA)
Max.
Voltage
Vmax
(V)
Max.
Current
Imax
(A)
 Reference
Temp
Tref
Dimension
(mm)
 @25C  @60C  Dmax  Tmax  Φd
AMZ11-03M151N265 150 ohm 20mA 15mA 50mA 265V 0.2A 80C 4.5 5.0 0.5
AMZ11-03M102N265 1000 ohm 10mA 7mA 20mA 265V 0.1A 4.5 5.0 0.5
AMZ11-03M152N265 1500 ohm 7mA 5mA 15mA 265V 0.1A 4.5 5.0 0.5
AMZ11-04M45RN265 45 ohm 40mA 30mA 80mA 265V 0.3A 5.5 5.0 0.6
AMZ11-05M601N420 600 ohm 20mA 16mA 40mA 420V 0.2A 6.5 5.0 0.6
AMZ11-05M232N420 2300 ohm 8mA 6mA 17mA 420V 0.1A 6.5 5.0 0.6
AMZ11-05M312N420 3100 ohm 5mA 4mA 13mA 420V 0.1A 6.5 5.0 0.6
AMZ11-07M251N265 250 ohm 25mA 20mA 50mA 265V 0.5A 8.0 5.0 0.6
AMZ11-07M112M550 1100 ohm 15mA 10mA 30mA 550V 0.5A 8.0 7.0 0.6
AMZ11-08M12RN265 12 ohm 120mA 70mA 220mA 265V 0.8A 9.0 5.0 0.6
AMZ11-03N151N265 150 ohm 30mA 25mA 60mA 265V 0.2A 100C 4.5 5.0 0.5
AMZ11-03N401N265 400 ohm 25mA 20mA 45mA 265V 0.2A 4.5 5.0 0.5
AMZ11-05N751N420 750 ohm 25mA 20mA 45mA 420V 0.2A 6.5 5.0 0.6
AMZ11-05P39RN265 39 ohm 85mA 70mA 170mA 265V 0.4A 120C 6.5 5.0 0.6
AMZ11-05P65RN265 65 ohm 70mA 60mA 140mA 265V 0.4A 6.5 5.0 0.6
AMZ11-05P601N420 600 ohm 20mA 16mA 39mA 420V 0.2A 6.5 5.0 0.6
AMZ11-05P122N550 1200 ohm 15mA 10mA 30mA 550V 0.1A 6.5 5.0 0.6
AMZ11-05P152N550 1500 ohm 12mA 7mA 24mA 550V 0.1A 6.5 5.0 0.6
AMZ11A-08P70RN420 70 ohm 64mA 50mA 127mA 420V 1.4A 8.5 7.0 0.6
AMZ11A-08P121N420 120 ohm 49mA 40mA 97mA 420V 1.4A 8.5 7.0 0.6
AMZ11A-08P151N420 150 ohm 43mA 35mA 86mA 420V 1.4A 8.5 7.0 0.6
AMZ11A-08P501N550 500 ohm 24mA 19mA 48mA 550V 1.0A 8.5 7.0 0.6

Note: If not specified, Resistance @25C (R25) tolerance shall be +/-30%.

AMWEI PTC Thermistor Circuit Protector Reliability Data

Test Item Standard Test conditions |ΔR25/R25|
Switching test at room temperature IEC 60738-1 Imax, Vmax, 50 cycles. <25%
Rapid change of temperature in air IEC600628-2-14,
Test Na
T=TLCT, T=TUCT 5 cycles,
30minutes.
<10%
Endurance at max. operating temperature
and max. operating voltage
IEC 60738-1 Ambient temperature: +60℃,
Maximum Operating Voltage,
Current limited to Imax.
Time: 24 hours
<25%
Storage in damp heat IEC 600628-2-3 Temperature of air: 40℃,
Relative humidity of air: 93%,
Duration: 56 days
<10%
Lead wire tensile IEC60068-2-21 Test Ua: pull strength 10N, 10 seconds,
Test Ub: bending 90°, pull strength 5N,
successively twice.
Test Uc: revolving 180°,
successively twice.
≤20%

How to select PTC thermistor circuit protector for overcurrent and overload protection?

In selecting PTC thermistor circuit protector for overcurrent and overload protection, following 5 factors should be taken into consideration.

1) Maximum operating voltage

PTC thermistor over-current protection device is connected in series in the circuit, in normal operating state, only a small portion voltage is on PTC thermistor protector. When PTC thermistorcurrent limiting devices is in high resistance state, it must bear almost all the power voltage.
Therefore in PTC thermistor protector model selection, it must have sufficient high operating voltage, and also power voltage fluctuation must be taken into consideration.

2) Rated current ( Non-trip current) and Switching current (Trip current)

PTC thermistor over-current protection device should have sufficient high rated current (that current at which the PTC thermistor protector will under no circumstances turn off) within the suitable voltage class.
Consider whether the overall layout of the circuit can handle the increased power for the short time until the PTC thermistor protector reduces it. Here a worst case estimate is necessary.

Rated current ( Non-trip current) and Switching current (Trip current) depend on the ambient temperature.
So, as the worst case for the rated current, the maximum permissible temperature for the application should be taken, and for the switching current the lowest possible ambient temperature.
In order to get reliable switching function, tripping current should be at least twice of non-trip current.

3) Maximum current permissible in maximum operating voltage

When PTC thermistor over-current protection device is required for protective function, it needs to check whether there is the case that the maximum permissible current, which has been listed in data sheet, has been exceeded.
Overloading the PTC thermistor protector by too high a switching current must be avoided, it may lead to PTC thermistor protector destroyed, or early failure.

4)Selection of PTC thermistor Reference Temperature (also called Switch temperature or Curie temperature)

AMWEI offer PTC thermistors for over-current protection with Reference Temperature 80 ℃, 100 ℃, 120 ℃, 140 ℃.
The rated current (non-trip current) depends on reference temperature and ceramic body diameter.
In consideration of cutting down cost, higher reference temperature and smaller dimension PTC thermistor current limiting devices shall be more economical, but it may leads to higher PTC thermistor surface temperature, and need to check whether it will cause undesired unfavorable effects.
Generally, reference temperature should be 20–40 ℃ higher than maximum operating ambient temperature.

5) PTC thermistor Application environmental effects

All due care should be taken, If there is any contact with chemicals or use of potting or sealing compounds.
The reduction of the titanate ceramic that can be caused by chemical effects on the surface of the thermistor and the resulting formation of low-resistance conducting paths.
Altered thermal relations in the sealant can lead to local overheating of the PTC thermistor protector and thus to failure.

 An example selecting AMWEI PTC thermistor for transformer overload protection

A transformer has

  • primary voltage 220V,
  • secondary voltage 16V,
  • secondary current 1.5A ,
  • primary current 330mA in abnormal condition,
  • it shall enter into protective state within 10 minutes.
  • Operating ambient temperature: -10C–+40C ,
  • temperature may rise 15–20C in normal operating state.
  • PTC thermistor will be installed near transformer.

Select an appropriate PTC thermistor part for primary protection.

1) Determine maximum operating voltage

Operating voltage 220V, considering power fluctuation, maximum operating voltage should be
220V x (1+20% ) =264V
Maximum operating voltage shall be 265V.

2) Determine non-trip current

According to calculation and actual measurement, primary current is 125mA in transformer normal operation.
In consideration the ambient temperature in installation position may reach to 60℃, Non-trip current in 60℃ should be 130–140mA.

3) Determine trip current

As the ambient temperature in PTC thermistor protector installation position may reach -10 ℃ , non trip current in -10 ℃ should be 320-330mA, tripping time within 5 minutes.

4) Determine PTC thermistor rated zero power resistance at 25 centigrade R25

PTC thermistor is in series in the primary circuit, the voltage decreasing should be possibly small, the heating power of PTC thermistor itself also maintain possibly small.
Generally, the voltage decreasing should be less than total power voltage 1%.
We can get R25 through calculation 220V X 1% ÷125mA=17.6Ω

5) Determine maximum current

Trough practical measurement, primary current can reach 500mA in transformer secondary circuit in short circuit state.
If considering that larger current may pass through PTC thermistor in the state of primary coil partial short circuit.
The maximum current should be more than 1A .

6) Determine reference (Curie)  temperature and dimension of PTC thermistor over-current protection device

Maximum ambient temperature in PTC thermistor protector installation position may reach 60C,  reference temperature should be 40C higher than that, then the reference temperature can be 100C.

In considering cutting down cost, also PTC thermistor is not installed in the transformer windings coil, higher surface temperature won’t have unfavorable effect to transformer.

Therefore reference (switch) temperature can also be 120 ℃,  and then the diameter of PTC thermistor can be smaller.

7) Determine PTC thermistor over-current protection device AMWEI part number.

Based on the above technical requirement, in reference of AMWEI technical data,  AMWEI part no. AMZ11-10P15RH265 shall be more appropriate.

  • Maximum operating voltage 265V,
  • Rated zero power resistance at 25C (R25) 15 Ω ± 25% ,
  • Non-trip current 140mA ,
  • Trip current 350 mA ,
  • Maximum current 1.5A ,
  • Reference temperature 120 ℃ ,
  • Diameter 11mm .

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PTC Thermistor Technology