OUTLINE： 　　ZMZ1 series of PTC thermistor are protective components which automatically protect and restore from abnormal temperature and current, also called "auto restore fuse" and "ten-thousand-time fuse". The operating principle is as indicated in the following figures. When a circuit is in the normal status, the current through PTC is lower than the rated current and PTC is in the normal state with small resistance value, which will not affect the normal operation of the protected circuit. In case of some trouble in the circuit and the current is greater than the rated current, the PTC will become hot quickly and present a high resistance state, which sets the circuit relatively "off" to protect the circuit from damage. After the trouble is removed, PTC will automatically restore its low resistance state and the circuit will resume normal operation. Normally, when PTC is used as an over-current protection component, it is preferred to select maximum operating current, maximum operating voltage and proper specifications. Furthermore such factors should be taken into consideration as the dimensions of the components, rated zero-power resistance, operating temperature range and etc. Relation between operating temperature, operating current and non-operating current is as shown in Fig.2. Operating current is normally 2~3 times non-operating current, and both of the currents will be reduced as operating temperature increases.