The MZ11 type PTC thermistor is widely 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, this component is also known as a "10,000-time fuse" or "self-recovery fuse." Due to its dual sensitivity to both temperature and current, it overcomes the limitations of traditional temperature switches that are not sensitive to current and standard fuses that are not responsive to temperature changes. This makes the PTC thermistor highly reliable, fast-acting, and cost-effective. It can be directly wound around transformer packages or mounted on circuit boards.
The working principle is straightforward: the PTC thermistor is connected in series with the load circuit. Under normal operating conditions, the current passing through the device is insufficient to raise its temperature above the Curie point, keeping it in a low-resistance state. However, when an overvoltage or overcurrent condition occurs, the resistance of the PTC thermistor increases rapidly by 3–4 orders of magnitude within a short time, effectively cutting off the current flow. Once the fault is cleared, the PTC thermistor automatically returns to its conductive state, restoring normal operation.
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 winding at 1.0Un, 1.2Un, and 1.9Un under normal load conditions.
2. For carrier tables, the ammeter should be directly integrated into the thermistor assembly circuit.
3. For three-phase electric meters, it is necessary to measure the current through the primary winding of the transformer when a single-phase power supply is applied at 1.0Un, 1.2Un, and 1.9Un.
4. Unless otherwise specified, the default maximum ambient operating temperature for the meter is 70°C.
5. Due to variations in process, instantaneous output power, and size among transformers operating at 1.9Un for four hours, it is generally not recommended to use transformers rated for 1.9Un for extended periods.
6. If transformers from different manufacturers are replaced or the same transformer is used on different power boards, it is advisable to re-measure relevant parameters and report them for confirmation.
7. If your product requires accurate metering across a wide voltage range (110V–440V), we recommend using a composite PTC thermistor for better performance.
Application Circuit
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