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Littelfuse TVS Diodes

Protect Designs with Transient Voltage Suppressors

Littelfuse TVS Diodes are used to protect semiconductor components from high-voltage transients. Their p-n junctions have a larger cross-sectional area than those of a normal diode, allowing them to conduct large currents to ground without sustaining damage. Littelfuse supplies TVS Diodes with peak power ratings from 200W to 30kW, and reverse standoff voltages from 5V to 600V. Littelfuse SMAJ, SMBJ, SMCJ, SMDJ, P6KE, and 1.5KE TVS devices are ideal for the protection of I/O Interfaces, Vcc bus and other vulnerable circuits used in Telecom, Computer, Industrial, and Consumer electronic applications.

• Low incremental surge resistance
  
• Unidirectional and Bidirectional polarities available
  
• Reverse standoff voltages range from 5 to 600V
  
• RoHS compliant-Matte Tin Pb-free plated
  
• Surface-mount power ratings from 200W to 5,000W
  
• Axial lead power ratings from 400W to 30,000W (30kW)
  
• High current protection available up to 15kA

• I/O Interfaces
  
• Vcc bus and other vulnerable circuits
  
• Telecom
  
• Computer
  
• Industrial
  
• Consumer Electronics

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.

• 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%
  

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

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 affect 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. The diagram at right shows a typical current waveform for induced lightning disturbances.