The Matching Function of Self Recovery Fuse and Overvoltage Protection Device in Preventing High Voltage Misconnection Protection

　　There are often testing requirements in circuit protection to prevent high voltage misconnections. In general, the self recovery fuse can be used in conjunction with overvoltage protection devices to prevent high-voltage misconnections. When high voltage is mistakenly connected to the circuit, the backend overvoltage protection device will quickly react, generate large currents, and limit the backend voltage to a certain range. The large current generated by the backend overvoltage protection device can quickly activate the , limit the total current of the system, and ensure that the backend overvoltage protection device will not be damaged due to long-term overcurrent.

　　The key to this cooperation is that after enduring surges for a long time, can quickly act and limit the circulating current before the backend overvoltage protection device reaches the limit value. Therefore, low current can more effectively cooperate with back-end overvoltage protection devices to prevent misconnection.

　　In addition to anti misconnection applications, it is also necessary to ensure that the maximum working voltage of is greater than the misconnection high voltage to prevent protection from failing due to insufficient maximum working voltage.

　　The following figure shows the XDSL line surge protection and power line contact protection scheme (according to the ITU K.21 standard in the communication industry, which requires AC220V 50Hz 15min testing). Generally, the front-end device uses a 470V ceramic gas discharge tube, while the back-end device uses a 190V semiconductor discharge tube. The selected is a BK250 low current type that can withstand a voltage of 250V.

　　When AC220V is connected, the front-end ceramic gas discharge tube does not act, while the back-end semiconductor discharge tube quickly acts, generating overcurrent. Then the acts to limit the current and ensure that the backend will not be damaged due to connecting to AC220V.

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