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The gas discharge tube (GDT) surge arrestor market is a relatively stable product technology in terms of innovation and new packaging. However, the latest design from Bourns Inc. could result in a new industry-standard form factor for the GDT market. Standard packages sizes for these circuit protection devices are typically 5 mm x 5 mm and 8 mm x 6 mm but Bourns has shrunk the package size by 75 percent through the use of a new design approach.
Bourns recently developed a new GDT series using a “breakthrough” flat package design that is said to set a new standard in volume and space-saving circuit protection, while maintaining the performance benefits of traditional GDT technology. The reason: The devices delivers a 75 percent savings in volume as compared to standard 8-mm GDTs. In addition, when vertically mounted, the new Model 2017 Series can support approximately twice the number of GDTs in the same board space.
“Electronics is continually being pushed to be smaller and to meet higher requirements for density and that results in components that need to be smaller with the same level of performance,” said Kurt Wattelet, product line manager at Bourns. “As designs become increasingly smaller, they are more and more susceptible to damage from transients such as lightning and voltage surges.”
“We’re trying to follow that same evolution and create robust but smaller devices to match the demands of the market,” Wattelet continued.
“Gas discharge tubes are still a very popular type of surge protection device due to their low capacitance, low leakage characteristics and high surge current handling capabilities, explained Wattelet. “Conventional GDT technology has been driven by a couple of different variables. Most common in the market are 5- x 5-mm and 8- x 6-mm sizes. The dimensions are critical because they effectively maintain the electrical isolation of the device and the size is also a factor in terms of how much energy it can handle and dissipate,” he said.
The diameter and the thermal mass provide much of the current handling capabilities for the GDT, Wattelet said. “Conventional GDTs offer reliable overvoltage protection but it does at the cost of PCB space.”
“There has been very little innovation in GDT design over the past 20 years so as engineers we look for different solutions to squeeze down device sizes," said Wattelet. "In this particular methodology, we reduce height, weight, and overall volume by up to 75 percent and still maintain the isolation and current-handling ability. The 75 percent is measured specifically against an 8- x 6-mm conventional GDT. The flat design also allows for flexibility and density, and achieving that in a couple of different form factors – horizontal and vertically mounted devices.”
The idea for the new design happened during a brainstorming session about handling components in mass production equipment, when Bourns’ engineering team started to question the dimensions of the devices, and why the GDT needed to maintain the 8-mm cylindrical size, said Johan Scliemann-Jensen, Bourns’ product development manager.
The engineering team decided to apply the design approach of high-voltage insulators and “wrinkle” the insulating pathways while maintaining the internal gap of the GDT, which enabled the device to be “compressed” in the axial direction to reduce the overall size.
“We essentially maintain the same isolating pathway and the same gap between the two electrodes. The physical gap and the gas pressure in the gas tube is what sets the voltage threshold for operation. With the design, we are able to maintain those as well as the conducting area of the GDT,” said Scliemann-Jensen.
The new devices target applications, particularly communications equipment, surge protection devices, and industrial controls, that need to save board space.
“If a customer doesn’t have a space issue then they will be inclined to buy the standard GDT,” said Wattelet. But he said there are customers in a number of industries that are looking to shrink the size of their circuit boards as they design thinner surge protection devices.
In one example, a surge protection device manufacturer in Germany had to cut holes into the plastic enclosure to accommodate the GDTs. With the new flat GDT, they don’t have to cut holes into the plastic enclosure to get the gas tubes to fit, Wattelet said.
The new series delivers a 75 percent savings in volume as compared to standard 8-mm Bourns GDTs.
The new Bourns FLAT GDT family is available in three flavors - 2015-xx-A 2017-xx-A No Leads, 2017-xx-SMH Horizontal Mount, and 2017-xx-SMC Vertical Mount. The new 2-electrode Model 2017 Series FLAT GDT combines a flat package and horizontal circuitry design, which was developed to meet the more sensitive overvoltage protection requirements of high-density and space-constrained applications such as telecommunications and industrial communications equipment, surge protective devices and PCB assemblies.
The Model 2017 Series is an ITU K.12 Class III GDT device rated at 10 kA on an 8/20 µs waveform. The series features DC breakdown voltages ranging from 90 to 500 V.
Of the three packages, Wattelet believes the horizontal will become the most common use of the package, which is very flat and low profile. The SMC version will be used in applications where there isn’t a height constraint but customers need to fit more GDTs on the circuit board. The “A” or leadless version is designed for more of a mechanical connection for cartridge or clamp fit applications.
Handling the new GDTs in production shouldn’t be a problem. Bourns worked with Fuji to develop the specific grippers and vacuum heads for these devices.
The 2017 series is set for worldwide release this month and will be available in volume production in the fourth quarter of 2015. The parts are manufactured in Bourns’ Costa Rica plant focused on highly automated and semi-automated manufacturing.
The Model 2017 FLAT is priced at $ 0.48 each in quantities of 1,000. Parts are available through Bourns’ distribution network including Digi-Key and Mouser.
Bourns also is in the process of developing a 3-electrode version of the FLAT series, combining two discrete 2-electrode versions in a single package. Samples should be available in the second quarter of 2016, followed by volume production in the third quarter.
