Prime Solutions in the Arsenal to Protect Power Electronics

Along with the demand for portability and increasing speed in technology, electronics are becoming more sensitive. Everything must fit into progressively more compact footprints and is expected to provide along service life. This means that circuit protection is not a luxury add-on or one-size-fits-all step in a power electronics design. Rather, it has become an area that requires attention and frequent customization to meet the reliability and safety requirements electronic system power ports demand. 

Semiconductor companies that offer controllers, processors, memory, and other integrated circuit products use a variety of Metal Oxide Semiconductor (MOS) technologies in their circuit protection devices. In contrast, Bourns employs bipolar semiconductor technology to produce robust and reliable protection devices. Bourns has been a leader in circuit protection for decades. In addition to the company’s deep technical knowledge, Bourns continuously invests in the company’s bipolar components portfolio adding innovative features and new device options. The bipolar technology advancements Bourns has made increases the speed and energy handling capabilities of the company’s bipolar devices making them excellent circuit protection solutions that can be applied across numerous applications.

The Case for Using PTVS Diodes

A pertinent example of bipolar technology is the power transient voltage suppression (PTVS) diode, which is designed to protect sensitive equipment from high voltage transient events. This is accomplished by clamping the incoming voltage to safe levels while absorbing excess energy. Typical threats to power ports include load switching transients and nearby lightning strikes. When the equipment is located outdoors, the power lines can act as antennae, collecting large amounts of transient energy. Equipment located in rural areas or mounted high on buildings or poles is difficult or expensive to access. Therefore, repair costs often are dominated by the labor required rather than the value of the equipment being replaced. Because semiconductor devices typically have longer lifespans 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 applications, 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.

"A pertinent example of bipolar technology is the power transient voltage suppression (PTVS) diode, which is designed to protect sensitive equipment from high voltage transient events"

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 competewith 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 theroutine 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. 

CAPTION:  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 increase.

Advancing PTVS Diode Designs

Because 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 aPTVS diodeiscut 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 stepsthat 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.

CAPTION:  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 protection.

Bourns’ 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.