Smaller. Lighter. Further.
By: Kevin Brooks, Technical Manager, APC Hi-Rel
Power components for military and aerospace applications are constantly being challenged to outperform their predecessors. With improvements delivered at each iteration, technology objectives are driving increased functionality combined with better efficiencies.
To deliver these improvements, whether representative of a groundbreaking innovation or incremental advancement, every component (and every engineer), in effect, must up its game.
DC-DC power systems are a critical part of this evolutionary process. Continuous downsizing, light-weighting and performance improvements have all been delivered to meet the innovation challenges of military and aerospace OEMs while simultaneously providing outstanding stability under typically harsh operating environments.
For this reason, OEM engineers will frequently seek to incorporate a complete power source from a single supplier, rather than creating a unique system from scratch. This not only saves design and testing time, but also frees up the in-house team to focus on other areas where their industry expertise is critical.
As a UK supplier of DC-DC technologies from a range of world leading manufacturers, our engineers are regularly asked by OEMs to advise on systems to meet specific application requirements. And, while all specifications are unique, there are several underlying ‘must haves’.
As a starting point, for military, aerospace and other high reliability applications, our experience shows that it’s best to choose DC-DC converters from a manufacturer that focuses on these applications. It’s important to look for high quality standards such as J-STD-001 and IPC-A-610 class 3. For the most critical applications, MIL-PRF-38534 Class H or Class K is the ideal route. Additionally, the environmental qualification should be to MIL-STD levels.
It’ll come as no surprise to find that when it comes to DC-DC power supplies, our engineers are continually challenged to deliver systems providing improvements in terms of size, weight and power (SWaP). At the same time, there is also a requirement for uncompromised (and better) stability across a wider environment range.
In reality, these improvements tend to represent an evolutionary process as opposed to a power revolution – but nonetheless, the progress is important and is delivering on OEM objectives.
A good example can be found in the DC-DC supplies developed by VPT. This USA-based specialist has been developing and supplying converters and filters for over 20 years, during which time it has powered some of the most advanced military and aerospace programs worldwide including: Civil / military aircraft systems, fighting vehicles, space solutions, marine systems and weapon systems.
VPT systems are also specified extensively for aerospace applications (see case study below).
VPT DC-DC systems are proving invaluable due to the organisation’s focus on SWaP and stability improvements. Recent power innovations include complete magnetic feedback without optocouplers for long-term reliability; well controlled under-voltage lockout circuitry to eliminate slow startup; and higher power with lower high-frequency noise.
One of the most recent innovations from VPT comes in the form of the HTD Series of DC-DC converters. Specifically designed for harsh and extreme temperature environments, these can be used in downhole and near engine environments. For example, the HTD isolated 1.5 Watt DC-DC converter operates from -55°C to +155°C while the non-isolated equivalent will operate up to +185°C.
VPT has also developed a six-sided rugged epoxy fully encapsulated V-SHIELD® package with integral metalised EMI shield. These encapsulated products withstand harsh environments including shock, vibration and thermal cycling and are fully compatible with aqueous cleaning processes – solving an often encountered manufacturing issue. In addition, the design incorporates space saving top and bottom heat sink interfaces. Critical factors include: stability between -55°C to +100°C with no power derating necessary; compliant with DO-160, DEF-STAN 59-411, DEF STAN 61-5 Part 6 Issue 5, MIL-STD-1275, MIL-STD-704, MIL-STD-461; and incorporates an input voltage range from 9V to 60V.
Case study: Powering ExoMars
VPT DC-DC converters were used on the ExoMars Trace Gas Orbiter launched from Kazakhstan by the European and Russian Space Agency Collaboration earlier this year. The converters were used on the UHF transceiver for the Lander and will also be fitted to the Rover for the 2018 mission.
The Lander is a test bed for technologies being used in future space programmes and also features VPT SV Series hybrid isolated power supplies, specified for their high reliability and ability to withstand the mission’s radiation levels and harsh operating environment.
It was critical that both power supplies and filters met Class K, the top level of screening and test for hybrids, frequently used for space missions to ensure the very highest level of reliability. Class K typically requires parts to be “burned in” for up to 320 hours at elevated temperatures, exposure to shock and vibration tests, and require pre-cap inspections.
Most importantly under the DLA (Defence Logistics Agency) approved radiation plan, MIL-PRF-38534 Appendix G, characterization and testing is performed at the critical semiconductor component piece-part level (radiation lot acceptance testing) from traceable semiconductor lots. This marks a fresh alternative from traditional suppliers where radiation testing has to be carried out after assembly. VPT SV Series power supply modules are one of the first to supply product with DLA radiation component testing, making them more cost and time efficient.