The MZ11 type PTC thermistor is commonly used in the power input terminals of various household appliances, instruments, and meters, as well as in communication lines and equipment for over-voltage, overheating, and lightning protection. In electronic engineering, it is also known as a "10,000 times fuse" or "self-recovery fuse." Due to its dual sensitivity to both temperature and current, it addresses the limitations of traditional temperature switches (which are not sensitive to current) and conventional fuses (which are not sensitive to temperature). This makes the PTC thermistor an ideal component with fast response, strong protection, and high reliability. It is a high-quality and cost-effective solution for circuit protection.
PTC thermistors can be directly wound into transformer packages or mounted on printed circuit boards. The protection mechanism works by connecting the PTC in the load circuit. Under normal operation, the current through the PTC is insufficient to raise its temperature above the Curie point, keeping it in a low-resistance state. However, if a fault occurs or an overvoltage causes a sudden surge in current, the PTC rapidly increases in temperature, causing its resistance to rise by 3–4 orders of magnitude within a short time, effectively cutting off the current. Once the fault is cleared, the PTC automatically returns to its conductive state.
Application Guide
1. For PTC thermistors used in primary over-voltage and over-current protection of transformers, the manufacturer should measure the current flowing through the primary side at 1.0Un, 1.2Un, and 1.9Un under normal load conditions.
2. For carrier tables, the ammeter should be directly connected to the thermistor assembly circuit.
3. For three-phase electric meters, the current through the primary of the transformer should be measured when the single-phase supply is at 1.0Un, 1.2Un, and 1.9Un.
4. Unless otherwise specified, the default maximum operating ambient temperature for the meter is 70°C.
5. Due to differences in manufacturing processes, output power, and volume, it's generally not recommended to use transformers that can withstand 1.9Un for four hours.
6. If transformers from different manufacturers are replaced or the same transformer is used on different power boards, it is advised to re-measure the relevant parameters and report them for confirmation.
7. If your product requires accurate metering under wide voltage ranges (110V–440V), it is recommended to use a composite PTC thermistor.
Application Circuit
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