RS232 / RS485 interface protection scheme

一、Applications:
1. The RS485/232 walk line is very long, easy to overpressure phenomenon
2. RS485/232 walk line outside, vulnerable to lightning strike
3. The RS485/232 walk line are susceptible to other line interference

二、 The scheme and matters needing attention:
1. The front end USES the large flow of GDT, leakage current.
2. The back-end using fast response time, TVS, low residual, effectively protect the RS485/232 chip.
3. The middle is PTC back lotus root, make the front GDT easier to action, to discharge current.
4. This solution meet IEC61000-4-2, GBT17626.2 standard, such as electrostatic IEC61000-4-5, GBT17626.5 surge standard, etc.
5. This scheme in differential mode and common mode adopts the same TVS and GDT, no dead Angle.
6. Mu S by 10/700 (equivalent 40 ohm internal resistance), 1.2/50-8/20 mu S test, concrete protection grade needs reference flow GDT and TVS.

三、 Project application:
1. The surveillance/security systems
2. The entrance guard system
3. The railway signal lamp control
4..Intelligent transportation system
5. Meters/meter, instruments and meters
6. Optical transceiver