How to Select PTC thermistors for Over Current Protection

Items to be checked
Selection criteria
How much (in volts) is the power supply voltage of the circuit in which PTC thermistor is used?
(Preventing PTC thermistor from being damaged)
-> Power supply voltage ≤ Maximum voltage of PTC thermistor
When the circuit is operating normally, how much (in amperes) is the current that flow through PTC thermistor?
(Preventing PTC thermistor from malfunctioning)
-> Normal current ≤ Non-operating current of PTC thermistor
When something abnormal such as a short circuit has occurred, how much (in amperes) is the current that flows through PTC thermistor?
(Ensuring reliable protection)
-> Abnormal current ≧ Operating current of  PTC thermistor
PTC thermistor application environment condition, esp. ambient temperature -> PTC thermistor reference temperature (also called Switch temperature or Curie temperature) >maximum operating ambient temperature

Related AMWEI PTC thermistors for Over Current Protection

1. PTC Thermistor Current Protect Resettable Fuse

For overcurrent overload protecion of 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.
Resistance @25C R25: 1-5000 ohm,
Maximum Operating Voltage(Vmax): 12-650V,
Non Operating (Non-trip) Current: 5-7000mA,
Switch temperature (reference temperature) 80C, 100C, 120c.
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2 Ceramic PTC Thermistor for Telecom High Voltage Current Surge Protection

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.
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.
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