Tvs Diode Array Spa Diodes Page 9 TVS Diode Array SPA Diodes Catalog

2017 Littelfuse, Inc. Specifications are subject to change without notice. Revised: 02/23/17 TVS Diode Arrays (SPA Diodes) Electrostatic Discharge (ESD) Electrostatic discharge is characterized by very fast rise times and very high peak voltages and currents. This energy is the result of an imbalance of positive and negative charges between objects. ESD that is generated by everyday activities can far surpass the vulnerability threshold of standard semiconductor technologies. Following are a few examples: Walking across a carpet: 35kV @ RH = 20%;1.5kV @ RH = 65% Walking across a vinyl floor: 12kV @ RH = 20%;250V @ RH = 65% Worker at a bench: 6kV @ RH = 20%;100V @ RH = 65% Vinyl envelopes: 7kV @ RH = 20%;600V @ RH = 65% Poly bag picked up from desk: 20kV @ RH = 20%;1.2kV @ RH = 65% Lightning Induced Transients Even though a direct strike is clearly destructive, transients induced by lightning are not the result of a direct strike. When a lightning strike occurs, the event creates a magnetic field which can induce transients of large magnitude in nearby electrical cables. A cloud-to-cloud strike will effect not only overhead cables, but also buried cables. Even a strike 1 mile distant (1.6km) can generate 70 volts in electrical cables. In a cloud-to-ground strike (as shown at right) the transient- generating effect is far greater. This diagram shows a typical current waveform for induced lightning disturbances. Inductive Load Switching The switching of inductive loads generates high energy transients which increase in magnitude with increasingly heavy loads. When the inductive load is switched off, the collapsing magnetic field is converted into electrical energy which takes the form of a double exponential transient. Depending on the source, these transients can be as large as hundreds of volts and hundreds of Amps, with duration times of 400 milliseconds. Typical sources of inductive transients include: Generator Motor Relay Transformer These examples are common in electrical 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 which exist in real world transients. Once these variables can be approximated, a suitable suppressor technology can be selected. The diagram at right shows a transient which is the result of stored energy within the alternator of an automobile charging system. A similar transient can also be caused by other DC motors in a vehicle. For example, DC motors power amenities such as power locks, seats and windows. These various applications of a DC motor can produce transients that are just as harmful to the sensitive electronic components as transients created in the external environment. T 1 V B V S = 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 PERCENT OF PEAK VALUE 100 90 50 10 O 1 t t 1 t 2 TIME Transient Voltage Threats and Scenarios (continued)

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