Yint Electronics Developed A Solution for the Characteristics of RS232 Transmission

RS232 is a standard for serial communication jointly developed by the American Electronics Industries Association (EIA), modem manufacturers, and computer terminal manufacturers. Its full name is "Technical Standard for Serial Binary Data Exchange Interface between Data Terminal Equipment (DTE) and Data Communication Equipment (DCE)".

It is used as a debugging port, an inter-board communication interface, and a monitoring signal interface on the communication equipment. The transmission distance is relatively short, the debugging is frequently used, and it is often plugged in and out, so the interface will receive the impact of overvoltage and overcurrent; When used for short-distance transmission connection, sometimes lightning strikes and strong electromagnetic interference will be sensed, which will cause damage to the interface chip. Yint Electronics has developed a solution for the characteristics of RS232 transmission.

Fig.1

General Requirements For Lightning Protectors:

●During normal operation, the connection of the lightning protector should not affect the normal transmission of the signal, the impedance of the lightning protector to the ground should be very large, and the impedance connected in series in the circuit should be very small.

●When lightning strikes the communication bus, the lightning protector should play a good voltage clamping role, and its clamping voltage should be lower than the withstand voltage level of the back-end control chip or other electrical devices.

●In the process of suppressing lightning attacks, the lightning protector itself should be intact.

●Lightning protectors should have a fast enough response to lightning strikes

Comprehensive Protection:

RS232 lightning protection overvoltage/live plugging/static protection

Fig.2

Device selection: 

●GDT: INT3R090L or INT3R090M
●TVS: According to the choice of power supply, generally choose SMBJ12CA or P6KE15CA for ±12V.
Pay attention to the selection of TVS3. TVS3 uses SMBJ24CA, but when the baud rate is relatively high because TVS has a large junction capacitance, it will affect the sending and receiving of signals. When the baud rate is greater than 9600, it is not recommended to use TVS3， you can see the test report for details.
●PPTC: 60V-010 or SMD1206-010
●Meet: IEC61000-4-5 10/700US 6KV /150A1.2/50US&8/20US 6KV /3KA
IEC61000-4-2 CONTACT DISCHARGE: 8KV AIR DISCHARGE: 15KV

±6KV surge test:

Fig.3

Comprehensive Protection:

RS232 overvoltage/hot plugging/electrostatic protection

Fig.4

This solution is suitable for high-reliability indoor data equipment such as PC industrial control and data room. It has lower requirements for anti-surge, mainly electrostatic protection requirements. This solution meets IEC61000-4-2 CONTACT DISCHARGE: 8KV AIR DISCHARGE: 15KV.