Structure and circuit design of signal surge protector

- Jul 26, 2019-

Signal Surge Protector (SPD) can be divided into telephone signal surge protector, network signal surge protector, control signal surge protector, high-power broadcast signal surge protector, monitoring signal wave according to the protected line. Surge protector, video signal surge protector, etc.

First, the telephone signal surge protector

The telephone line is a symmetrical double line, which can also be regarded as a parallel line. Its working power supply has DC 48V, ring voltage 90V, and operating frequency is 64kbits/s. Therefore, the surge protector used on this line should meet the DC action. The voltage is greater than 190V and less than 260V, and the impact breakdown voltage is less than 700V. Therefore, the surge protector is generally required to withstand a lightning strike voltage of 4kV and a lightning strike current of 5kA or more.

Second, RS232 interface surge protector

RS232 communication lines are generally divided into several types: one is a direct connection method for a 25-pin cable line; the other is a direct connection method for a twisted pair; and the other is a twisted pair cable with a modem at both ends, and then converted into a 25-pin cable. . There are also RS232 boards with 15-pin and 9-pin connectors. Different protection modes can be used for different communication line modes. Since the operating voltage of the RS232 interface is below 15V and the transmission rate is several hundred kbits/s, the insertion loss in the working frequency range is not more than 1dB. Therefore, the parameter selection of the RS232 surge protector should be determined that the DC clamp voltage is not less than 15V, the impact clamp voltage is not more than 26V, the transmission rate is not less than 1Mkbits/s, the withstand voltage is not less than 1.5kV, and the lightning current resistance is not less than 3kA.

Third, RS485 interface surge protector

The RS485 communication line has a 9-pin cable connection, but more is a twisted pair connection. Different protection modes can be used for different communication line modes. Since the operating voltage of the RS485 interface is below 12V, the transmission rate is 100kbits/s, and the insertion loss in the working frequency range is not more than 1dB. Therefore, the parameters of the RS485 interface surge protector are selected: DC clamp voltage is not less than 12V, impact clamp The voltage is not more than 22V, the transmission rate is not less than 1Mkbits/s, the withstand voltage is not less than 1.5kV, and the lightning current resistance is not less than 3kA.

Fourth, E1 interface surge protector

E1's 2Mkbits/s interface line types are twisted pair, coaxial line and RJ45 network type, but essentially one loop for receiving and transmitting. The signal level of the E1 line is generally not more than 3V, and the transmission rate is 2047kbits/s. Therefore, the parameter selection of the surge protector of the E1 interface should be determined when the DC clamp voltage is not greater than 5V, the impact clamp voltage is not greater than 20V, and the transmission is performed. The rate is not less than 2Mkbits/s, the insertion loss is not more than 1dB in the working frequency range, the withstand voltage is not less than 1.5kV, and the lightning current resistance is not less than 5kA.

Five, coaxial line surge protector

Ordinary coaxial interface surge protector, such as BNC interface type, has two kinds of circuits, one is to treat the outer skin as ground, only consider the protection of the outer core of the core; the other is that the outer skin is not directly grounded, the surge protector In addition to considering the protection of the core wire to the outer skin, there is also protection of the outer skin to the ground. This type of surge protector has low lightning-impedance capability on the communication line, so the lightning-resistant current capability is not high. Generally, the lightning-resistant current of 10kA is sufficient. However, due to the high communication frequency band, the requirements for attenuation and standing wave ratio are relatively high. Generally, the insertion loss of the working frequency band is not more than 0.2 dB, and the standing wave ratio is not more than 1.1.