When selecting PPTC (Resettable Fuses), the following key circuit parameters need to be considered:
1. Operating ambient temperature: Determine the working ambient environmental temperature of the PPTC, because the ambient temperature will affect its performance and working characteristics.
2. Normal operating current (Ihold): This is the maximum current that the PPTC can withstand under normal operating conditions without causing its resistance value to suddenly change. The selected PPTC should ensure that its Ihold is greater than the normal operating current of the circuit.
3. Trip current (Itrip): This is the minimum current that can cause the resistance value of the PPTC to suddenly increase. Usually Itrip is twice Ihold. When selecting, ensure that the fault current (Imax) is between Itrip and Ihold.
4. Maximum voltage (Vmax): Ensure that the rated voltage of the PPTC is greater than the operating voltage of the circuit to avoid breakdown damage.
5. Maximum current (Imax): This is the maximum current that the PPTC can withstand at the rated voltage. The selected PPTC should ensure that its Imax is higher than the possible fault current in the circuit.
6. Trip time (Ttrip): Confirm whether the response time of the PPTC meets the protection requirements of the circuit, which usually needs to be between a few milliseconds and tens of milliseconds.
7. Power consumption (Pd): Ensure that the power consumption of the PPTC is within an acceptable range in the active state to prevent overheating.
8. Zero power resistance (R): Ensure that the static resistance of the PPTC when it is not powered meets the design requirements.
9. Package/form factor: Select the appropriate package/form factor according to the circuit design, such as through-hole type, surface mount type, etc., for easy installation.
Comprehensive consideration of these parameters will help you select the appropriate PPTC to ensure its effective protection performance in the circuit.