In the rapidly advancing world of electronics, circuit protection is critical to ensuring equipment and system longevity, reliability, and safety. One of the latest innovations in this field is snapback TVS (transient voltage suppressor) technology. While no device is perfect for all applications, the advancement of snapback TVS technology brings the industry closer to the ideal solution for protecting many applications across various markets, including consumer electronics where warranty returns can consume entire profit margins.
This article begins with some comments on the technology and market trends that are driving adoption of TVSs. It then provides an overview of conventional TVS devices, discussing their pros and cons, starting with historical solutions like SCRs, and then moving onto the currently used gas discharge tubes, metal oxide varistors, and TVSs.

With that as background, the article describes how snapback TVS device technology offers a groundbreaking approach to circuit protection compared to previous TVS methods and devices. The characteristics and behavior of snapback TVSs are discussed with some data presented to illustrate the differences between conventional and snapback TVSs. This leads to a discussion of application benefits and an application example.

The Growing Need For TVS Protection

First, some history on transient voltage suppression is needed. The real world is replete with both natural and manmade transient electrical energy. In the beginning, most electronics didn’t really need much protection from these events, but when electronics applications transitioned from solid-state to integrated-circuit—and now to VLSI—technologies, each generation became more sensitive to transients and surges. Circuit protection became increasingly necessary on ac and dc power lines and on the I/O connectivity that makes equipment work in the real world.

Lighting applications, for example, until a short time ago were 100% electric and employed electronics based on magnetics and capacitors for their ballast designs. Then the lighting industry moved to using more complex and sensitive electronics, from high-frequency switching electronic ballasts for fluorescent lighting, to the now ubiquitous LED lighting systems that use electronic drivers. Today, proximate lightning and utility equipment switching events cause plenty of transients that can damage lighting electronics. Add to this challenge that manufacturers often require warranties of five, seven, and even 10 years—despite these electronics being more susceptible to damage.
Along with the challenge of protecting more-sensitive electronic systems, electronics designers must conduct industry qualification testing and meet a number of specifications for many applications worldwide. These include IEC61000-4-2/3/4/5 and the IEEE C62.41 ringing waveform testing, as well as tests for automotive such as ISO and SAE specifications ISO7637-2 or ISO16750-2.

Evolving TVS Technology

Before describing snapback TVS technology, let’s explore the historical approaches to mitigating electrical transients. The purpose of a TVS device is to convert transient electrical energy into transient thermal energy and to dissipate it as heat. One of its primary goals is to dissipate this heat energy as quickly as possible and then reset for another event.
One of the first TVS solutions was the SCR clamp. Although it worked, this device was very prone to false triggering. Proximate noise, either conducted or radiated, entering the circuit triggered the SCR until the power source was recycled and the current through the SCR went to zero. This was not an option for equipment needing 100% uptime and, for that reason, SCR clamps aren’t really used today.

Another early technology, gas discharge tubes, or GDTs, were mainly used as circuit protection in the era of copper telecommunications lines to protect against lightning strikes. They are still widely used in a plethora of applications, often in combination with other protection devices. Among other benefits, GDTs are reasonably fast-responding. However, they have a limited lifetime and degrade with repeated application of transients depending on the magnitude of the transient.
In the 70s, we saw the invention of the MOV (metal oxide varistor). This device was a significant step forward in TVS technology, offering many benefits and few downsides. However, both MOVs and gas tubes can fail short and thus require the addition of series current-limiting devices like fuses and circuit breakers.
From the late 70s to the mid-80s, semiconductor TVS devices were developed, and were available in both bi- and uni-directional options. Semiconductor TVS device have fast response times and good thermal performance with a lifespan that can be limited by simply not overdissipating (overheating) the die too far above 175°C. They are more precise and rugged than previous methods—unless they are overdissipated.

Table 1 compares the characteristics of the traditional TVS devices described above. All of these technologies have drawbacks in precision, accuracy, and temperature coefficient. For example, MOVs are not able to withstand multiple transient events. I have seen MOVs turned into talcum powder with a couple of leads sticking out of the board as a result of too much repetitive transient energy being applied.
In addition, all types have a tempco issue in which the clamping voltage tends to change with temperature. It’s not only the ambient temperature that’s a concern in this regard but also the repetitive pulses that can heat up the protection device. This behavior is a problem since, as stated earlier, a key function of a TVS device is to dissipate the heat from the transient being converted into thermal energy.