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Multilayer ceramic capacitors and varistors provide UAV power systems with performance & design advantages

Mon, 12/23/2013 - 1:09pm
Pat Hollenbeck, Field Applications Engineer, Advanced Operations, AVX

The power systems designed into today’s advanced military and aerospace applications are incorporating increasingly sophisticated components and design topologies to achieve improved efficiency, weight reduction, and performance enhancements. Two essential criteria for realizing the cutting edge, energy efficient power systems required for high-reliability military avionics applications, such as unmanned aerial vehicles (UAV) (Figure 1), are controlling power quality and voltage stability.


UAVs, originally designed for combat and surveillance missions too dangerous for manned aircrafts, are becoming more common in diverse applications, including: search and rescue, coastal and terrain mapping, traffic and security surveillance, and even border patrol. As a result of this more widespread use of UAVs, improving the performance, efficiency, and reliability of the power systems that they rely upon have become major design considerations.

Typical flight durations for unmanned aircraft missions can extend from several hours to several days, so efficient power conversion, power conditioning, and battery management systems are critical design considerations for improving UAV performance. Incorporating advanced electromagnetic interference (EMI) filtering and transient voltage suppression into UAV power systems are two effective methods for improving system robustness and efficiency. Controlling EMI significantly improves output voltage quality, which results in faster switching frequencies and more effective power conversion, and transient voltage suppression ensures that the power electronics can withstand high voltage spikes –such as lightning strikes, electrostatic discharge (ESD) events, and other forms of fast rise time transients– all of which are possible scenarios when considering both everyday and military operations. Consequently, high-reliability passive electronic components, such as multilayer ceramic capacitors (MLCCs) and multilayer varistors (MLVs), are essential in UAV power systems.

The development and implementation of stringent new military specifications and flight requirement standards, such as DO-160 Environmental Conditions and Test Procedures for Airborne Equipment, has encouraged the development of enhanced MLCC, MLV, and hybrid MLCC/MLV component designs capable of providing improved reliability and performance in mission-critical power systems applications. These rigorous testing procedures, which simulate or even exceed millions of equivalent component hours of constant field use, measure performance specifications such as lightning immunity, in-rush current, and load impedance discharge and qualify only the most robust designs capable of withstanding these situations while still providing peak performance. For example, DO-160 surge voltage waveforms comprise very short rise times to mimic a typical lightning strike event. As such, these tests result in extremely high surge currents and require robust, high-reliability parts specifically designed to withstand such extreme instances.

In response to these stringent military and flight requirement specifications, several new, next-generation series of miniature ceramic capacitors for EMI filtering and multilayer varistors for transient voltage suppression have been developed for use in the power conversion, power conditioning, and battery management systems of the high frequency power supplies designed into mission-critical avionics. These miniature, application-specific devices exhibit maximized capacitance values, optimized parasitics, and improved transient voltage characteristics that enable high frequency power conversion and more stable output voltage characteristics. 

Recent advancements in the materials systems, internal electrode designs, and leadframe configurations of MLCCs have resulted in high volumetric efficiency EMI filter capacitors capable of enabling lightweight UAVs that require less propulsion and power to remain airborne. For example, MLCCs placed on the I/O lines of a power supply or converter suppress EMI noise and reduce voltage ripple, which improves output voltage quality. New MLCC designs also feature minimized parasitics, such as equivalent series resistance (ESR) and equivalent series inductance (ESL), which enable higher switching frequencies in power supplies and converters, effectively improving the overall efficiency of UAV power management systems.

Similar materials and design updates incorporated into next-generation multilayer varistors have resulted in their ability to provide advanced voltage clamping in a single chip, effectively suppressing transient voltages and protecting sensitive electronics from high voltage spikes. The turn-on time for these devices is also faster than any silicon transient voltage suppression (SiTVS) diode, diverting more energy and current away from the IC than any other circuit protection device available (Figure 2). Additionally, MLVs have multiple strike capabilities, high peak inrush current capabilities, high thermal stability, and EMI/RFI (radio-frequency interference) suppression capabilities.


Capable of providing complete solutions for EMI filtering and transient voltage suppression, advanced new MLCC, MLV, and hybrid MLCC/MLV component technology developed in response to stringent new military specifications and flight requirements continues to enable the development of high efficiency, high performance, lightweight, robust, and dependable power systems for use in UAV and other mission-critical, high-reliability applications.

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