Mini Radial Leaded 12 ohm PTC Thermistor , Vishay BC Components
Quick Details
1. Used in the frequent-switching,typical switching life can pass over 100,000 times;
2. High reliability, good performance of safety and stability;
3. Wide operating temperature range;
-25 ~ +125℃(when V=0V)
0~ +60℃(when V=Vmax)
4. The withstanding voltage can reach to over 420-1000VAC;
5. The resistance will not drift in normal temperature.
6. Small dimension
7. Complete specifications
8. Stable delayed time
Description
Ceramic PTC (positive temperature coefficient) thermistors are used instead of conventional fuses to protect load, such as motors, transformers, or electronic circuit, against overcurrent for circuit protection. PTC thermistor 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.
Application
It 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.
Specification
PTC Thermistor outline and dimension (mm)
PTC Thermistor for Overload Over-current Protection 265V/250V Series Data
| Part number | Resistance
@25C
R25
(OHM) | Non-trip
current
Int(mA) | Trip current
@25C
It
(mA) | Max.
operating
voltage
Vmax
(V) | Max.
current
Imax
(A) | Reference
temperature
Tref
(Centigrade) | Dimension
(mm) |
| @25C | @60C | Dmax | Tmax | Φd |
| MZ11-20P3R7H265 | 3.7 ohm | 530mA | 430mA | 1050mA | 265V | 4.3A | 120C | 22.0 | 5.0 | 0.6 |
| MZ11-16P6R0H265 | 6.0 ohm | 390mA | 300mA | 780mA | 265V | 3.1A | 17.5 | 5.0 | 0.6 |
| MZ11-16P7R0H265 | 7.0 ohm | 350mA | 280mA | 700mA | 265V | 3.1A | 17.5 | 5.0 | 0.6 |
| MZ11-13P10RH265 | 10 ohm | 260mA | 200mA | 520mA | 265V | 1.8A | 14.0 | 5.0 | 0.6 |
| MZ11-13P12RH265 | 12 ohm | 225mA | 180mA | 450mA | 265V | 1.8A | 14.0 | 5.0 | 0.6 |
| MZ11-12P10RH265 | 10 ohm | 250mA | 200mA | 500mA | 265V | 1.8A | 13.5 | 5.0 | 0.6 |
| MZ11-12P101H265 | 100 ohm | 50mA | 40mA | 100mA | 265V | 1.8A | 13.5 | 5.0 | 0.6 |
| MZ11-10P15RH265 | 15 ohm | 180mA | 140mA | 350mA | 265V | 1.2A | 11.0 | 5.0 | 0.6 |
| MZ11-10P39RH265 | 39 ohm | 130mA | 100mA | 250mA | 265V | 1.2A | 11.0 | 5.0 | 0.6 |
| MZ11-08P15RH250 | 15 ohm | 150mA | 120mA | 300mA | 250V | 0.8A | 9.0 | 5.0 | 0.6 |
| MZ11-08P25RH265 | 25 ohm | 130mA | 100mA | 250mA | 265V | 0.8A | 9.0 | 5.0 | 0.6 |
| MZ11-08P35RH265 | 35 ohm | 115mA | 90mA | 225mA | 265V | 0.8A | 9.0 | 5.0 | 0.6 |
| MZ11-08P45RH265 | 45 ohm | 105mA | 80mA | 200mA | 265V | 0.8A | 9.0 | 5.0 | 0.6 |
| MZ11-08P55RH265 | 55 ohm | 90mA | 70mA | 180mA | 265V | 0.8A | 9.0 | 5.0 | 0.6 |
| MZ11-07P82RH265 | 82 ohm | 70mA | 50mA | 140mA | 265V | 0.6A | 8.0 | 5.0 | 0.6 |
| MZ11-07P56RH265 | 56 ohm | 90mA | 60mA | 175mA | 265V | 0.6A | 8.0 | 5.0 | 0.6 |
| MZ11-06P33RH250 | 33 ohm | 110mA | 85mA | 200mA | 250V | 0.4A | 7.0 | 4.5 | 0.6 |
| MZ11-05P70RH265 | 70 ohm | 65mA | 50mA | 130mA | 265V | 0.3A | 6.5 | 5.0 | 0.6 |
| MZ11-05P85RH265 | 85 ohm | 60mA | 45mA | 120mA | 265V | 0.3A | 6.5 | 5.0 | 0.6 |
| MZ11-05P39RH250 | 39 ohm | 80mA | 65mA | 160mA | 250V | 0.2A | 6.5 | 5.0 | 0.6 |
| MZ11-05P121H265 | 120 ohm | 45mA | 35mA | 90mA | 265V | 0.3A | 6.5 | 5.0 | 0.6 |
| MZ11-05P181H265 | 180 ohm | 40mA | 30mA | 80mA | 265V | 0.3A | 6.5 | 5.0 | 0.6 |
| MZ11-04P70RH250 | 70 ohm | 50mA | 40mA | 100mA | 250V | 0.2A | 5.5 | 5.0 | 0.6 |
| MZ11-04P121H265 | 120 ohm | 40mA | 30mA | 80mA | 265V | 0.2A | 5.5 | 5.0 | 0.6 |
| MZ11-03P151H250 | 150 ohm | 40mA | 30mA | 75mA | 250V | 0.2A | 4.5 | 5.0 | 0.5 |
| MZ11-10N12RH250 | 12 ohm | 170mA | 130mA | 340mA | 250V | 1.2A | 100C | 11.0 | 5.0 | 0.6 |
| MZ11-10N18RH265 | 18 ohm | 145mA | 110mA | 290mA | 265V | 1.2A | 11.0 | 5.0 | 0.6 |
| MZ11-10N22RH265 | 22 ohm | 125mA | 90mA | 250mA | 265V | 1.2A | 11.0 | 5.0 | 0.6 |
| MZ11-07N22RH250 | 22 ohm | 120mA | 90mA | 225mA | 250V | 0.5A | 8.0 | 5.0 | 0.6 |
| MZ11-05N151H265 | 150 ohm | 38mA | 30mA | 80mA | 265V | 0.3A | 6.5 | 5.0 | 0.6 |
| MZ11-05N301H265 | 300 ohm | 27mA | 20mA | 55mA | 265V | 0.3A | 6.5 | 5.0 | 0.6 |
| MZ11-05N601H265 | 600 ohm | 20mA | 15mA | 40mA | 265V | 0.2A | 6.5 | 5.0 | 0.6 |
| MZ11-05N102H265 | 1000 ohm | 15mA | 12mA | 30mA | 265V | 0.2A | 6.5 | 5.0 | 0.6 |
| MZ11-04N151H265 | 150 ohm | 36mA | 28mA | 80mA | 265V | 0.3 | 5.5 | 5.0 | 0.6 |
| MZ11-03N151H265 | 150 ohm | 33mA | 25mA | 65mA | 265V | 0.2A | 4.5 | 5.0 | 0.5 |
| MZ11-03N101H250 | 100 ohm | 40mA | 30mA | 80mA | 250V | 0.2A | 4.5 | 5.0 | 0.5 |
| MZ11-03N70RH250 | 70 ohm | 45mA | 35mA | 90mA | 250V | 0.1A | 4.5 | 5.0 | 0.5 |
| MZ11-08M12RH250 | 12 ohm | 120mA | 70mA | 220mA | 250V | 0.8A | 80C | 9.0 | 5.0 | 0.6 |
| MZ11-08M25RH265 | 25 ohm | 85mA | 50mA | 170mA | 265V | 0.8A | 9.0 | 5.0 | 0.6 |
| MZ11-08M35RH265 | 35 ohm | 80mA | 50mA | 150mA | 265V | 0.8A | 9.0 | 5.0 | 0.6 |
| MZ11-08M50RH265 | 50 ohm | 60mA | 40mA | 120mA | 265V | 1.0A | 9.0 | 5.0 | 0.6 |
| MZ11-07M101H265 | 100 ohm | 50mA | 30mA | 100mA | 265V | 0.6A | 8.0 | 5.0 | 0.6 |
| MZ11-05M70RH250 | 70 ohm | 50mA | 30mA | 100mA | 250V | 0.3A | 6.5 | 5.0 | 0.6 |
| MZ11-05M121H265 | 120 ohm | 30mA | 20mA | 60mA | 265V | 0.3A | 6.5 | 5.0 | 0.6 |
| MZ11-03M101H250 | 100 ohm | 25mA | 18mA | 55mA | 250V | 0.2A | 4.5 | 5.0 | 0.5 |
| MZ11-03M151H265 | 150 ohm | 22mA | 15mA | 45mA | 265V | 0.2A | 4.5 | 5.0 | 0.5 |
Note: If not specified, Resistance @25C (R25) tolerance shall be +/-25%.
PTC Thermistor for Overload Over-current Protection 140V Series
| Part Number | Resistance
@ 25C
R25
(OHM) | Non-trip
current
Int(mA) | Trip
current
@25C
It
(mA) | Max.
operating
voltage
Vmax
(V) | Max.
current
Imax
(A) | Reference
temperature
Tref
(Centigrade) | Dimension
(mm) |
| @25C | @60C | Dmax | Tmax | Φd |
| MZ12-20P2R6H140 | 2.6 ohm | 650mA | 500mA | 1300mA | 140V | 4.3A | 120C | 22.0 | 5.0 | 0.6 |
| MZ12-16P4R7H140 | 4.7 ohm | 425mA | 330mA | 850mA | 140V | 3.1A | 17.5 | 5.0 | 0.6 |
| MZ12-16P5R6H140 | 5.6 ohm | 400mA | 310mA | 800mA | 140V | 3.1A | 17.5 | 5.0 | 0.6 |
| MZ12-13P6R8H140 | 6.8 ohm | 325mA | 250mA | 650mA | 140V | 1.8A | 14.0 | 5.0 | 0.6 |
| MZ12-12P5R6H140 | 5.6 ohm | 325mA | 250mA | 650mA | 140V | 1.8A | 13.5 | 5.0 | 0.6 |
| MZ12-12P6R8H140 | 6.8 ohm | 300mA | 230mA | 600mA | 140V | 1.8A | 13.5 | 5.0 | 0.6 |
| MZ12-10P10RH140 | 10 ohm | 225mA | 170mA | 450mA | 140V | 1.2A | 11.0 | 5.0 | 0.6 |
| MZ12-10P6R8H140 | 6.8 ohm | 275mA | 200mA | 550mA | 140V | 1.2A | 11.0 | 5.0 | 0.6 |
| MZ12-08P22RH140 | 22 ohm | 135mA | 110mA | 270mA | 140V | 0.8A | 9.0 | 5.0 | 0.6 |
| MZ12-06P25RH140 | 25 ohm | 125mA | 90mA | 250mA | 140V | 0.5A | 7.0 | 5.0 | 0.6 |
| MZ12-05P33RH140 | 33 ohm | 90mA | 70mA | 175mA | 140V | 0.3A | 6.5 | 5.0 | 0.6 |
| MZ12-16R2RIH140 | 2.1 ohm | 710mA | 570mA | 1420mA | 140V | 3.1A | 140C | 17.5 | 5.0 | 0.6 |
| MZ12-13R3R8H140 | 3.8 ohm | 500mA | 400mA | 1000mA | 140V | 1.8A | 14.0 | 5.0 | 0.6 |
| MZ12-10R15RH140 | 15 ohm | 210mA | 170mA | 420mA | 140V | 1.2A | 11.0 | 5.0 | 0.6 |
| MZ12-10R6R7H140 | 6.7 ohm | 300mA | 230mA | 600mA | 140V | 1.2A | 11.0 | 5.0 | 0.6 |
| MZ12-10R10RH140 | 10 ohm | 250mA | 200mA | 500mA | 140V | 1.2A | 11.0 | 5.0 | 0.6 |
| MZ12-08R12RH140 | 12 ohm | 200mA | 160mA | 400mA | 140V | 0.6A | 9.0 | 5.0 | 0.6 |
Note: If not specified, Resistance @25C (R25) tolerance shall be +/-25%.
PTC Thermistor for Overload Over-current Protection 60V Series
| Part Number | Resistance
@ 25C
R25
(Ω) | Non-trip
current
Int(mA) | Trip
current
@25C
It
(mA) | Max.
operating
voltage
Vmax
(V) | Max.
current
Imax
(A) | Reference
temperature
Tref
(Centigrade) | Dimension
(mm) |
| @25C | @60C | Dmax | Tmax | Φd |
| MZ13-16P2R3H60 | 2.3 ohm | 550mA | 450mA | 1100mA | 60V | 8.0A | 120C | 17.5 | 4.0 | 0.6 |
| MZ13-12P3R7H60 | 3.7 ohm | 380mA | 320mA | 750mA | 60V | 5.5 | 13.5 | 4.0 | 0.6 |
| MZ13-10P5R6H60 | 5.6 ohm | 300mA | 250mA | 600mA | 60V | 4.3A | 11.0 | 4.0 | 0.6 |
| MZ13-08P9R4H60 | 9.4 ohm | 180mA | 150mA | 360mA | 60V | 3.0A | 9.0 | 4.0 | 0.6 |
| MZ13-05P25RH60 | 25 ohm | 100mA | 85mA | 200mA | 60V | 1.0A | 6.5 | 4.0 | 0.6 |
| MZ13-03P55RH60 | 55 ohm | 60mA | 50mA | 120mA | 60V | 0.7A | 4.5 | 4.0 | 0.5 |
| MZ13-08M4R7H60 | 4.7 ohm | 180mA | 120mA | 360mA | 60V | 3.0A | 80C | 9.0 | 4.0 | 0.6 |
Note: If not specified, Resistance @25C (R25) tolerance shall be +/-25%.
PTC Thermistor Current Limiting Devices for Transformer Over-current Overload Protection 265V, 100C
(For application of PTC thermistor protector installation inside transformer windings coil)
| Part number | Resistance
@25C
R25
(OHM) | Non-trip
current
Int (mA) | Trip
current
@25C
It
(mA) | Max.
operating
voltage
Vmax
(V) | Max.
current
Imax
(A) | Reference
temperature
Tref
(Centigrade) | Dimension
(mm) |
| @25C | @80C | Dmax | Tmax | Φd |
| MZ11-05N121H265 | 120 ohm | 45mA | 25mA | 90mA | 265V | 0.4A | 100C | 6.5 | 5.0 | 0.6 |
| MZ11-05N151H265 | 150 ohm | 38mA | 20mA | 80mA | 265V | 0.4A | 6.5 | 5.0 | 0.6 |
| MZ11-07N22RH265 | 22 ohm | 110mA | 60mA | 220mA | 265V | 0.7A | 8.0 | 4.5 | 0.6 |
| MZ11-07N32RH265 | 32 ohm | 95mA | 50mA | 190mA | 265V | 0.7A | 8.0 | 4.5 | 0.6 |
| MZ11-07N55RH265 | 55 ohm | 70mA | 40mA | 140mA | 265V | 0.7A | 8.0 | 5.0 | 0.6 |
| MZ11-08N30RH265 | 30 ohm | 100mA | 55mA | 200mA | 265V | 1.0A | 9.0 | 5.0 | 0.6 |
| MZ11-08N35RH265 | 35 ohm | 90mA | 50mA | 180mA | 265V | 1.0A | 9.0 | 5.0 | 0.6 |
| MZ11-08N40RH265 | 40 ohm | 85mA | 45mA | 170mA | 265V | 1.0A | 9.0 | 5.0 | 0.6 |
| MZ11-08N39RH265 | 39 ohm | 95mA | 50mA | 180mA | 265V | 1.2A | 9.5 | 5.0 | 0.6 |
| MZ11-08N25RH265 | 25 ohm | 110mA | 60mA | 220mA | 265V | 1.2A | 9.5 | 5.0 | 0.6 |
| MZ11-10N22RH265 | 22 ohm | 125mA | 70mA | 250mA | 265V | 1.5A | 11.0 | 5.0 | 0.6 |
| MZ11-10N18RH265 | 18 ohm | 145mA | 80mA | 290mA | 265V | 1.5A | 11.0 | 5.0 | 0.6 |
| MZ11-10N12RH265 | 12 ohm | 170mA | 95mA | 340mA | 265V | 1.5A | 11.0 | 5.0 | 0.6 |
| MZ11-12N18RH265 | 18 ohm | 180mA | 100mA | 360mA | 265V | 2.0A | 13.5 | 5.0 | 0.6 |
| MZ11-12N12RH265 | 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%.
PTC Thermistor Current Limiting Devices for Transformer Over-current Overload Protection 265V 120C
(For application of PTC thermistor protector installation outside transformer windings coil)
| Part number | Resistance
@25C
R25
(OHM) | Non-trip
current
Int(mA) | Trip
current
@25C
It
(mA) | Max.
operating
voltage
Vmax
(V) | Max.
current
Imax
(A) | Reference
temperature
Tref
(Centigrade) | Dimension
(mm) |
| @25C | @60C | Dmax | Tmax | Φd |
| MZ11-16P6R0H265 | 6.0 ohm | 390mA | 300mA | 780mA | 265V | 3.1A | 120C | 17.5 | 5.0 | 0.6 |
| MZ11-13P10RH265 | 10 ohm | 260mA | 200mA | 520mA | 265V | 1.8A | 14.0 | 5.0 | 0.6 |
| MZ11-12P10RH265 | 10 ohm | 250mA | 200mA | 500mA | 265V | 1.8A | 13.5 | 5.0 | 0.6 |
| MZ11-10P15RH265 | 15 ohm | 180mA | 140mA | 350mA | 265V | 1.2A | 11.0 | 5.0 | 0.6 |
| MZ11-08P25RH265 | 25 ohm | 130mA | 100mA | 250mA | 265V | 0.8A | 9.0 | 5.0 | 0.6 |
| MZ11-08P35RH265 | 35 ohm | 115mA | 90mA | 225mA | 265V | 0.8A | 9.0 | 5.0 | 0.6 |
| MZ11-08P45RH265 | 45 ohm | 105mA | 80mA | 200mA | 265V | 0.8A | 9.0 | 5.0 | 0.6 |
| MZ11-08P55RH265 | 55 ohm | 90mA | 70mA | 180mA | 265V | 0.8A | 9.0 | 5.0 | 0.6 |
| MZ11-05P70RH265 | 70 ohm | 65mA | 50mA | 130mA | 265V | 0.3A | 6.5 | 5.0 | 0.6 |
| MZ11-03P151H250 | 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%.
PTC Thermistor current limiting devices for measuring instrumentation and meter overload and short circuit protection, Voltage 265V/420V/550V, Reference Temperature 80C, 100C, 120C
| Part number | Resistance
@25C
R25
(OHM) | Non-trip
current
Int(mA) | Trip current
@25C It
(mA) | Max. operating
voltage
Vmax
(V) | Max. current
Imax
(A) | Reference
temperature
Tref
(Centigrade) | Dimension
(mm) |
| @25C | @60C | Dmax | Tmax | Φd |
| MZ11-03M151N265 | 150 ohm | 20mA | 15mA | 50mA | 265V | 0.2A | 80C | 4.5 | 5.0 | 0.5 |
| MZ11-03M102N265 | 1000 ohm | 10mA | 7mA | 20mA | 265V | 0.1A | 4.5 | 5.0 | 0.5 |
| MZ11-03M152N265 | 1500 ohm | 7mA | 5mA | 15mA | 265V | 0.1A | 4.5 | 5.0 | 0.5 |
| MZ11-04M45RN265 | 45 ohm | 40mA | 30mA | 80mA | 265V | 0.3A | 5.5 | 5.0 | 0.6 |
| MZ11-05M601N420 | 600 ohm | 20mA | 16mA | 40mA | 420V | 0.2A | 6.5 | 5.0 | 0.6 |
| MZ11-05M232N420 | 2300 ohm | 8mA | 6mA | 17mA | 420V | 0.1A | 6.5 | 5.0 | 0.6 |
| MZ11-05M312N420 | 3100 ohm | 5mA | 4mA | 13mA | 420V | 0.1A | 6.5 | 5.0 | 0.6 |
| MZ11-07M251N265 | 250 ohm | 25mA | 20mA | 50mA | 265V | 0.5A | 8.0 | 5.0 | 0.6 |
| MZ11-07M112M550 | 1100 ohm | 15mA | 10mA | 30mA | 550V | 0.5A | 8.0 | 7.0 | 0.6 |
| MZ11-08M12RN265 | 12 ohm | 120mA | 70mA | 220mA | 265V | 0.8A | 9.0 | 5.0 | 0.6 |
| MZ11-03N151N265 | 150 ohm | 30mA | 25mA | 60mA | 265V | 0.2A | 100C | 4.5 | 5.0 | 0.5 |
| MZ11-03N401N265 | 400 ohm | 25mA | 20mA | 45mA | 265V | 0.2A | 4.5 | 5.0 | 0.5 |
| MZ11-05N751N420 | 750 ohm | 25mA | 20mA | 45mA | 420V | 0.2A | 6.5 | 5.0 | 0.6 |
| MZ11-05P39RN265 | 39 ohm | 85mA | 70mA | 170mA | 265V | 0.4A | 120C | 6.5 | 5.0 | 0.6 |
| MZ11-05P65RN265 | 65 ohm | 70mA | 60mA | 140mA | 265V | 0.4A | 6.5 | 5.0 | 0.6 |
| MZ11-05P601N420 | 600 ohm | 20mA | 16mA | 39mA | 420V | 0.2A | 6.5 | 5.0 | 0.6 |
| MZ11-05P122N550 | 1200 ohm | 15mA | 10mA | 30mA | 550V | 0.1A | 6.5 | 5.0 | 0.6 |
| MZ11-05P152N550 | 1500 ohm | 12mA | 9mA | 24mA | 550V | 0.1A | 6.5 | 5.0 | 0.6 |
| MZ11A-08P70RN420 | 70 ohm | 64mA | 50mA | 127mA | 420V | 1.4A | 8.5 | 7.0 | 0.6 |
| MZ11A-08P121N420 | 120 ohm | 49mA | 40mA | 97mA | 420V | 1.4A | 8.5 | 7.0 | 0.6 |
| MZ11A-08P151N420 | 150 ohm | 43mA | 35mA | 86mA | 420V | 1.4A | 8.5 | 7.0 | 0.6 |
| MZ11A-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%.
PTC Thermistor Protector Reliability data
| Test | 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 | GB2423.29 | Test Ua: pull strength 10N, 10 seconds,
Test Ub: bending 90°, pull strength 5N,
successively twice.
Test Uc: revolving 180°,
successively twice. | ≤20% |
Reference information in selecting PTC thermistor over-current protection devices for overcurrent and overload protection.
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 thermistor current 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)
The 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 Reference temperature (also called Switch temperature or Curie temperature)
We can offer PTC thermistor 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, high reference temperature and small 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) Application environmental effects
If there is any contact with chemicals or use of potting or sealing compounds, all due care should be taken. 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. And the altered thermal relations in the sealant can lead to local overheating of the PTC thermistor protector and thus to failure.
An example of PTC thermistor over-current protection devices part selection for overload protection of power transformer.
An 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. Please 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 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 temperature and dimension of PTC thermistor over-current protection device
Maximum ambient temperature in PTC thermistor protector installation position may reach 60 ℃ , reference temperature should be 40 ℃ higher than that, then the reference temperature can be 100 ℃ . 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 temperature can also be 120 ℃ , and then the diameter of PTC Thermistor can be smaller.
7) Determine PTC thermistor over-current protection device part number.
Based on the above technical requirement, in reference of our technical data, AMZ11-10P15RH265 shall be more appropriate.
Maximum operating voltage 265V, rated zero power resistance at 25C (R25) 15 Ω±20% , non-trip current 140mA , trip current 350 mA , maximum current 1.5A , reference temperature 120 ℃ , diameter 11mm .
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