The first space-qualified GaN DC-to-DC power converter

08 August 2019

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DC-to-DC power supplies convert a DC input voltage to output of a different voltage level. For space applications, this typically involves conversion of voltage from power sources such as solar arrays or batteries into the proper voltage for communication, sensing, or control electronics. These devices are typically complete functional modules, although others are ICs that may require additional electronics. The advantages of utilizing standard, complete functional modules are short lead time, low development costs, and often high performance. This enables designers to focus on their product, instead of on developing power supplies.

Spacecraft DC power converters must meet specialized requirements that are not typical for terrestrial DC power converters. They must be ruggedized to withstand severe launch shock and vibration environments, large temperature fluctuations, and exposure to harsh radiation in space environments. Since payload weight, volume, and power consumption are at a premium, spacecraft DC power converters must be engineered with a lightweight, compact footprint while maximizing energy efficiency. They must also exhibit extremely high levels of reliability, since it is impossible to replace them if they fail.

DC-DC converters for spacecraft

The use of high-efficiency DC power converters can result in huge dividends for spacecraft systems. High efficiency results in low power consumption, which reduces the size and mass of power source components, such as solar arrays and batteries. Since less electrical energy is lost and dissipated as heat, a high-efficiency DC power converter can use small, light heat sinks and other electrical components. The converter can be packaged in a compact, lightweight, thermally insulated and radiation-hardened enclosure. At the spacecraft system level, these benefits are realized in less mass and volume of power sources such as solar arrays and batteries, thermal and radiation control treatments, structure and fuel for station-keeping, and orbital maintenance.

Typical switching DC power converters operate by switching metal oxide silicon field effect transistors (MOSFETs) on and off with a controller to achieve the desired voltage. High efficiency is achieved by quickly charging and discharging the MOSFETs. This is due to the fact that power loss is at its greatest when the switch is in transition between on and off states. The high switching frequency also minimizes energy usage per switching cycle, leading to smaller components, such as capacitors and filters, enabling the DC power supply to have a smaller size.

Silicon to GaN

Silicon has been the material of choice for semiconductor transistors and power MOSFETs due to its outstanding electrical properties and relatively low production cost. Over the years, silicon transistors have experienced widespread usage, since according to Moore’s law, it was possible to double its performance, with a reduction in cost, every 18 months. However, silicon MOSFETs have more recently reached a point of diminishing returns due to practical limitations in switching speed and electrical resistance in the silicon material itself.

Alternative materials have been investigated that could meet the speed, resistance and cost requirements to satisfy Moore’s Law. Gallium nitride (GaN) has demonstrated electrical conductivity 1,000 times more efficient than silicon. This increased conductivity enables GaN field effect transistors (FETs) to match the functional performance of silicon FETs with a smaller size. This in turn enables production of more GaN FETs on a single semiconductor wafer, reducing manufacturing costs. Furthermore, GaN FETs can switch hundreds of volts in nanoseconds, boosting its switching frequency to the multi-megahertz range. This enables the use of more compact electrical components, further reducing the size of the DC power converter. The increased conductivity and high switching frequency also leads to low resistance losses and heat generation, enabling a reduction of heat sink mass. These advantages allow a DC power converter using GaN FETs to have a smaller size, higher efficiency and lower cost than one using silicon MOSFETs.

SGRB DC-DC converters, from VPT

Figure 1. SGRB DC-to-DC power converter. Source: VPTFigure 1. SGRB DC-to-DC power converter. Source: VPT

VPT Engineering has recently introduced the SGRB DC-DC converter series, this will be the first commercially available, space-qualified, GaN-based, DC-to-DC converter platform available to the market (Figure 1). It is designed to work in harsh radiation environments and incorporates built-in EMI filtering. More specifically, the SGRB has been characterized to total ionizing dose (TID) of 100 krad (Si), including enhanced low dose rate sensitivity (ELDRS), and single event effects (SEE) performance to 85 MeV/mg/cm2.

The SGRB DC-DC converter utilizes GaN FETs, which enable it to achieve an exceptionally high efficiency of up to 95%. As a result, the SGRB package is smaller, more compact and lightweight compared to its MOSFET counterparts. It has a 100 V input and a 28 V, 400 W output and is rated for full power operation from -35° C to 85° C. Furthermore, the SGRB DC-DC converter uses a fixed-frequency, reduced-voltage switching topology that results in low input and output noise, making it ideal for use in space telecommunication systems. A summary of performance specifications for the SGRB DC-DC converter is shown below in Figure 2.

Figure 2. SGRB performance specifications. Source VPTFigure 2. SGRB performance specifications. Source VPT

VPT’s history of proven space-flight heritage ensures long-term performance and reliability. The SGRB is designed in accordance with MIL-HDBK-1547 and is manufactured in a state-of-the-art facility, which is certified to ISO9001, J-STD-001 and IPC-A-610.

VPT is a global leader in the development and production of power conversion solutions for use in avionics, military, space and industrial applications. Their products include a wide range of high- reliability DC-DC converters, EMI filters, accessory power products, and custom engineering services for the rapid development of critical power systems, which are designed and engineered to the highest industry standards.

VPT is part of the Heico Electronic Technologies Group, which serves a majority of the world’s airlines and numerous defense and space contractors and military agencies. VPT’s research and development headquarters are in Blacksburg, Virginia, with manufacturing in certified facilities at Delta Electronics in Taiwan and at PPI-Time Zero in Virginia. Sales and marketing facilities are located in the aerospace hub of Seattle. VPT offers sales representation in more than 30 countries.

More information about VPT and its products can be found on the VPT website.

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