Power transformers are commonly used components in electronic products. They are widely used because of their simplicity and ease of manufacture. There are two types of step-up transformers and step-down transformers (without impedance transformers and line matching transformers), because the original AC voltage is After proportionally increasing or decreasing, the output is supplied to the load, so it is also called linear transformer. In the application, the step-up transformer is mainly applied to instrumentation; for the power supply of electronic products, the actual step-down transformer is mostly. Structurally, the transformer consists of a laminated silicon steel sheet and primary and secondary coils. The coils are mostly made of enamelled copper wire and are now also wrapped with enameled aluminum wire.
Nowadays, transformer manufacturers choose copper wire or aluminum wire winding according to customers' different uses and different products. It is easy to have the following problems: When the equipment works, the heat is much higher, the temperature can reach 70-80 °C, but the transformer can work. However, the paint of the enameled wire is prone to aging, cracking, leakage, or sparking between wires, which greatly shortens the life of the transformer.
These problems have been used in the past for the overcurrent protection of the glass fuse in the primary, and also the temperature fuse and the application of the bimetal thermostat for over-temperature protection installed on the outside of the transformer package. The application of the disposable fuse is easy to produce frequent replacement. Inconvenience, the application of the bimetal thermostat is prone to the failure of the fault load in the case of continuous power to expand the fault range.
It is necessary to solve the problem of over-temperature and over-current protection without replacing the fuse, and also failing to turn on the faulty circuit after protection. At present, only the PPTC self-recovering fuse can achieve this purpose.
PPTC self-recovery fuses can be selected according to different circuits, different current voltage and temperature requirements, and can be connected to the primary or secondary of the transformer. In normal operation, it is low resistance. When the transformer exceeds the specified temperature, When it exceeds the specified current, it will instantly become a high resistance, which limits the current of the circuit and protects the transformer. When the power is turned off or the fault is automatically restored to low resistance, the transformer returns to the normal state, and the uninterrupted power will not be automatically restored. It will not cause the fault load to be re-opened under the uninterrupted power condition and expand the fault range. It solves the problem of timely protection of over-temperature and over-current without replacing the fuse.
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