Electromagnetic Compatibility - 5

What is the meaning of 8/20us and 10/1000us waveform?

This is a transient waveform used in surge immunity tests. As shown in the waveform, the first parameter of 8us (micro-seconds) is the rise time of the waveform and 20us is the pulse duration. The pulse duration is the time from t=0 (starting of the pulse) to time where the pulse from peak drops to 50% of the peak. Apart from rise time and fall time the transient can also be characterized by the slew rate and is measured in kV/us. 8/20us is a class 2 transient waveform which can occur beacuase of internal distrubances. 10/1000us is a class 1 transient waveform which can occur beacause of external distrubances. IEC 61000-4-5 standard covers the transient immunity test. The transient waveform (or surge) is basically a short burst of over voltage condition that can occur in a live system due to lighting type of conditions. Also, these bursts can because of sudden load transients. Varistor, Spark Gap, Gas arrestors are the kind of devices are used in parallel to the circuit to protect the device from surges. TVS diodes with good energy handling capacbility can also be used. We see Transil diodes with good power handling capacity used for protection. Basically, these diodes help in overvoltage clamping.