Vishay’s New Voltage Suppressors Feature 3 kW Surge Capacity

Vishay Intertechnology’s surface-mounted TransZorbs, released last Wednesday, are TVS diodes available in surfaced-mounted SMC (DO-214AB) packages, purposed for automotive, industrial, and telecom applications. Designated as the SMC3KxxxCAHM3A series, there are 33 separate devices with standoff voltage ranging from 10 to 120 V.

 

Vishay’s TransZorb bidirectional TVS diodes. Screenshot used courtesy of Vishay Intertechnology

 

Today’s vehicles, be they conventional or EVs, can be likened to “computers on wheels.” And although we still tend to think of the industrial environment as the dominion of tough, bulky, mechanically-controlled machines, that world too is populated by digital devices that are as vulnerable to short-lived voltage spikes as their vehicular counterparts.

Enter the TVS, whose job is to react to pulses and absorb them before they can damage sensitive circuitry. At the same time, TVS must not hamper normal signal propagation, and thus interfere with the operation of the circuit. 

Below, we’ll provide background on some of the technical terms used when describing TVS, before discussing some additional specifications defining Vishay’s latest offerings. 

 

Standoff Voltage

The standoff voltage is the maximum voltage the TVS can be counted on to not disturb. For example, to protect a device that receives a 5 V data signal, the TVS’s standoff voltage must be greater than 5 V.

 

Breakdown Voltage and Clamping Voltage

It’s very easy to confuse breakdown voltage and clamping voltage. 

Breakdown voltage is the voltage across the TVS that causes it to start reacting; below that voltage, current across the diode is close to zero. The stability of breakdown voltage is critical to the predictable operation of the TVS, and Vishay specifies minimum and maximums within tight limits.

Clamping voltage, somewhat higher than breakdown voltage, is the voltage level above which the TVS will not allow the line to go, unless the diode itself becomes incapacitated.

 

Peak Power Pulses

The diode can break down if it is forced to absorb too much current, depending on the nature of the power pulse. 

A “10/1000 µs” pulse rises to its peak in 10 µs, and declines to 50% of that peak in 1000 µs. As advertised, members of Vishay’s new series can absorb 3 kW of this type of pulse.

 

A 10/1,000 µsec pulse. Image [modified] used courtesy of Vishay Intertechnology

 

There is also the well-known “8/20 µs” pulse, which rises to its peak in 8 µs, and declines to 50% of that peak in 20 µs. When subjected to this pulse, members of the SMC3KxxxCAHM3_A series can manage up to 30 kW.

 

Select Specifications

These new TVS are all bidirectional. Leakage current — the very slight current that flows across the diode even below the standoff voltage — ranges from 1 to 10 µA. For additional specifications, complete details can be found in the series datasheet. 

 

Applications

TVS diodes are widely applicable across the whole spectrum of electronics. Per Vishay’s release announcing its new series, these TVS are aimed in particular at providing protection against automotive “load dump.” 

This phenomenon can occur in a vehicle when the alternator is charging the battery and the discharged battery loses connectivity, releasing dangerous transients that must be protected against. The international regulation that defines load-dump testing is ISO 16750-2, tests A and B.

 

Regulatory Notes

Series members are RoHS-compliant and halogen-free.

 

Physical Considerations

The new TRANSZORBs operate over a temperature range of -55 to +175 °C. Most importantly, the breakdown voltages are stable over this entire temperature range. Approximate size for the SMC (DO-214AB) package is 0.27 x 0.33 inches. 

 

Feature image [CC BY 2.0] used courtesy of Vishay Intertechnology