Mlv Design Guide Page 3 Introduction-Common Transient Events

and electronic systems. Because the sizes of the loads vary according to the application, the wave shape, duration, peak current, and peak voltage are all variables that exist in real-world transients. Once these variables are approximately calculated or measured, a suitable suppressor technology can be selected. Figure 2. Automotive Load Dump The above figure shows a transient resulting from stored energy within the alternator of an automobile charging system. A similar transient can be generated by other DC motors in a vehicle. For example, DC motors are used to power amenities like power locks, seats, and windows. These DC motor applications can produce transients that do as much damage to sensitive electronic components as transients that occur in the external environment. Lightning-Induced Transients A lightning direct strike is clearly destructive; transients induced by lightning are the result of a strike occurring nearby. When a lightning strike occurs, it creates a magnetic field that can induce transients of large magnitude in nearby electrical cables. Figure 3 shows how a cloud-to-cloud strike will affect both overhead and buried cables. Even a strike around one mile distance (1.6km) can generate 70V in electrical cables. Figure 3. Cloud-to-Cloud Lightning Strike T 1 V B V B = 25V to 125V V B = 14V T= 40ms to 400ms V S 90% 10% t V T 1 = 5ms to 10ms R = 0.5 to 4 Figure 4 shows the effect of a cloud-to-ground strike; the transient-generating effect is far greater. Figure 4. Cloud-to-Ground Lightning Strike Figure 5 shows a typical current waveform for induced lightning disturbances. Figure 5. Peak Pulse Current Test Waveform Transient Threats Vs. Sensitivity of the Electronics System Even though they occur in a timeframe of nanoseconds, ESD events can be very harmful to sensitive electronics. The high voltage level of an ESD pulse can punch through the SiO2 of the MOSFET and other IC chips and damage the system permanently. Figure 6 shows a circuit board damaged by an ESD event. Buried Line Transient Generated: 70 V at 1.6km (1 mile) 10 kV at 150m (160 yards) 100m 1km 10km 11kV 1100 V 110 V t 1 t 2 100 90 50 10 O 1 TIME PERCENT OF PEAK VALUE 2016 Littelfuse Multilayer Varistors (MLVs) Design Guide www.littelfuse.com Surface Mount Multilayer Varistors (MLVs) Design Guide Introduction - Common Electrical Transient Events (continued) 3

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