9May - June - 2022value of the equipment being replaced. Because semiconductor devices typically have longer life spans than other types of components, PTVS diodes can be a good choice for applications where zero maintenance is a priority. A growing need for circuit protection is in applications that operate from 48 VDC power lines. One reason may be that 48 V is considered the highest voltage humans can touch without fear of serious shock. Within 48 V applications, designers of 5G radio sites, e-bike chargers, PoE equipment, and servers are more and more often specifying PTVS devices for protection. Another growth area for PTVS diodes is the 400 VDC, 600 VDC and even 800 VDC application, such as electric vehicle, solar energy and server farm applications. While it could be simple to overprotect these types of higher power applications and call it a day, such an approach is not a responsible approach if it increases the price or device complexity unnecessarily. Clamping devices such as PTVS diodes have been around for decades, and the broad range of available options allows designers to select the right solution based on cost, size, package type, and degree of effectiveness.Comparing PTVS Diodes and MOVs PTVS diodes compete with metal oxide varistor (MOV) devices. While both are voltage clamping devices, they differ in two key respects. PTVS diodes offer lower clamping voltages than MOVs, and PTVS diodes do not experience the routine degradation issues that affect an MOV's lifespan. To solve this issue, designers often place as many as a half dozen MOVs in parallel in order to decrease the clamping voltage and extend the life of the MOVs. However, one properly specified PTVS diode will clamp as much as 300 V lower than the MOV combination, offering enhanced reliability and potentially reducing downstream component costs. In contrast to how an MOV reacts, after an initial short duration peak, the voltage across a PTVS diode folds back to a lower level and then remains relatively constant as the current through the device continues to increaseAdvancing PTVS Diode DesignsBecause of the breadth of power electronics applications that need circuit protection, there are a variety of package requirements. For instance, lead inductance that can cause voltage peaks during transient events was recognized as problematic in some designs so Bourns added surface mount packages to its portfolio. Surface mount packages are also more compatible with pick and place equipment and metal substrate PCBs. Bourns conducts ongoing research to find methods of overcoming design challenges for bipolar structures. The silicon die in a PTVS diode is cut from very thin wafers processed on both sides. This creates a bidirectional device, whereas MOS devices are processed on thicker wafers and only on one side. Perhaps counterintuitive, thinner wafers produce higher performance diodes. In addition, any non-uniformity in the semiconductor junctions formed in the wafer can lead to "current crowding" that effectively limits the surge handling capability. Bourns is a leader in the advancement of proprietary processing steps that help ensure uniform breakdown to prevent current crowding, enabling the company to offer some of the highest surge handling ratings in the industry. Furthermore, the bidirectional aspect of PTVS designs on thin wafers creates P-N-P or N-P-N structures that can begin to exhibit transistor-like characteristics at high surge currents. This creates voltage "fold-back" during surge events. This fold-back characteristic significantly helps reduce the increase in clamping voltage and the resulting power dissipation at higher currents, but it must be managed so as not to interfere with the power port operation. For this and other purposes,Bourns actively utilizes semiconductor modeling as the pathway to future enhancements. Understanding how bipolar-based protection can help increase longevity and safety in existing and next-generation power electronics, Bourns is dedicated to making continued advancements in the development of new products. Remaining invested in bipolar technology, Bourns' PTVS diode product offering currently includes multiple working voltages at current ratings of 1 kA, 3 kA, 6 kA, 10 kA, and 15 kA surge protectionBourns' future product roadmap includes expanding surge and voltage capabilities as well as innovative new packages.For reliability, stability and surge protection performance, Bourns® PTVS diodes are capable protection solutions for an increasing variety of sensitive power electronics.
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