In the rapidly evolving domain of urban air mobility and low-altitude communication networks, the electrical power system of an eVTOL (Electric Vertical Take-Off and Landing) aircraft serving as a communication relay is not merely a power source. It is the critical "aerial power nexus" that dictates mission endurance, communication stability, payload capacity, and operational safety. Its performance hinges on achieving extreme power density, unparalleled reliability under dynamic flight loads, and ultra-efficient energy utilization across all subsystems. These requirements are fundamentally anchored in the judicious selection and systemic integration of power semiconductor devices.
This analysis employs a holistic, mission-oriented design philosophy to address the core challenges within an eVTOL relay's power chain. We focus on selecting the optimal power switches for three critical nodes—the high-voltage propulsion inverter, the essential DC-DC power conversion stage, and the intelligent, multi-channel auxiliary load management—under stringent constraints of weight, volume, thermal management in thin air, and resilience to vibration and wide temperature swings.
From the provided portfolio, three key devices are selected to form a cohesive, high-performance power solution tailored for high-end, low-altitude communication relay eVTOL applications.
I. In-Depth Analysis of the Selected Device Combination and Application Roles
1. The Propulsion Powerhouse: VBM18R20S (800V, 20A, TO-220, SJ-Multi-EPI) – High-Voltage Main Propulsion Inverter Switch
Core Positioning & Topology Deep Dive: This 800V Super-Junction MOSFET is engineered for the high-voltage bridge legs of the multi-phase propulsion motor inverter. In eVTOLs utilizing 600-800V battery packs for reduced current and cable weight, its 800V VDS rating provides robust margin against line transients and regenerative spikes during aggressive descent or autorotation. The Super-Junction (Multi-EPI) technology delivers an excellent balance of low specific on-resistance (240mΩ @10V) and fast switching capability.
Key Technical Parameter Analysis:
Efficiency at Altitude: The low RDS(on) directly minimizes conduction losses in the motor drives, which are the single largest power consumer. This translates to extended loiter time for the communication relay mission and reduced thermal load, a critical advantage where convective cooling is limited.
High-Frequency Operation Potential: Compared to planar high-voltage MOSFETs, its SJ structure allows for potentially higher switching frequencies, enabling smaller and lighter motor filter inductors and capacitors—a significant benefit for weight-sensitive aerospace design.
Robustness: The TO-220 package offers a proven, reliable mechanical interface for mounting to a liquid-cooled or advanced air-cooled heatsink, essential for managing heat in the compact nacelle of an eVTOL propulsion unit.
2. The Versatile Power Converter Core: VBE16I07 (600/650V IGBT+FRD, 7A, TO-252) – Isolated DC-DC or Auxiliary Inverter Switch
Core Positioning & System Benefit: This IGBT with co-packaged Fast Recovery Diode is ideal for medium-power, medium-frequency switching applications within the power train. Its primary role could be in a critical, isolated DC-DC converter that steps down the high-voltage bus (e.g., 800V) to a stable intermediate voltage (e.g., 270V or 48V) for avionics and communication payloads, or as a switch in a dedicated motor drive for ancillary systems like a hydraulic pump.
Key Technical Parameter Analysis:
Balanced Performance for Medium Frequency: At switching frequencies typical for aerospace-grade DC-DC converters (10kHz-30kHz), the IGBT's combination of a low VCEsat (1.65V @15V) and integrated FRD often presents a more favorable total loss and robustness profile compared to MOSFETs, especially in hard-switching topologies.
Integrated FRD for Simplicity: The built-in diode ensures reliable and efficient reverse conduction, simplifying the power stage layout and enhancing reliability by eliminating a discrete diode component—a key advantage for vibration-prone environments.
TO-252 for Compactness: The DPAK (TO-252) package offers a superior footprint-to-performance ratio, allowing for a dense power converter design crucial in the constrained airframe of an eVTOL.
3. The Intelligent Auxiliary Load Director: VBC8338 (Dual N+P, ±30V, SOP8) – Redundant Low-Voltage Bus & Payload Power Management Switch
Core Positioning & System Integration Advantage: This dual complementary MOSFET (N+P) in a compact SOP8 package is the cornerstone of intelligent, solid-state power distribution for low-voltage subsystems (e.g., 28V, 12V). It enables sophisticated load management for communication payloads, flight control computers, sensors, and lighting.
Application Example: Can be configured as a high-side (P-channel) and low-side (N-channel) pair for a single load, enabling advanced diagnostics like current sensing via the low-side, or used independently to control two separate critical rails with bidirectional blocking capability.
PCB Design & Control Value: The extreme integration saves vital PCB real estate. The complementary pair allows for elegant circuit designs, such as active OR-ing for redundant power supplies, ensuring continuous operation of critical communication gear.
Reason for Complementary Pair Selection: The combination provides unparalleled design flexibility. The P-MOS allows simple logic-level control for high-side switching without charge pumps, while the N-MOS offers very low RDS(on) (22mΩ @10V) for minimal loss in low-side or load-return path applications. This is ideal for managing numerous, frequently cycled avionic loads.
II. System Integration Design and Expanded Key Considerations
1. Topology, Drive, and Control Synergy
Propulsion Inverter & Motor Controller: The gate drive for the VBM18R20S must be synchronized with the high-speed field-oriented control (FOC) algorithms. Isolated gate drivers with reinforced insulation are mandatory for safety and noise immunity.
DC-DC Converter Control: The VBE16I07, used in a phase-shifted full-bridge or similar topology, requires a driver matched to its IGBT characteristics (e.g., negative turn-off bias for robustness). Its controller must implement precise soft-start and fault protection.
Digital Load Management: The VBC8338 gates are controlled by the Vehicle Management Computer or a dedicated Power Distribution Unit (PDU) microcontroller. This enables features like in-rush current limiting (soft-start), sequential power-up, priority-based load shedding, and real-time health monitoring of each channel.
2. Hierarchical and Weight-Optimized Thermal Management
Primary Heat Source (Liquid Cooling): The VBM18R20S in the propulsion inverter will be the primary heat source. It must be mounted on a liquid-cooled cold plate integrated into the propulsion system's cooling loop.
Secondary Heat Source (Forced Air/Conduction): The VBE16I07 in the DC-DC converter will require a dedicated heatsink, possibly cooled by forced air from a dedicated blower or via conduction to a primary cold plate.
Tertiary Heat Source (PCB Conduction & Ambient): The VBC8338 and associated management circuitry will rely on thermal vias and copper pours on the PCB to dissipate heat to the surrounding airframe or a thermally conductive enclosure.
3. Engineering for Aerospace-Grade Reliability
Electrical Stress Protection:
VBM18R20S: Requires careful snubber design across each switch to dampen voltage ringing caused by parasitic inductance in the high-di/dt propulsion circuit.
VBE16I07: The DC-DC transformer's leakage inductance necessitates an RCD snubber to clamp turn-off voltage spikes.
VBC8338: Inductive loads (relays, solenoids) must have flyback diodes. TVS diodes should protect against load dump and ESD events on the power rails.
Enhanced Gate Protection: All gate drives must be designed with low inductance, series resistance for damping, and clamping Zeners. Redundant pull-down/pull-up resistors ensure failsafe states.
Conservative Derating Practice:
Voltage Derating: VBM18R20S operating VDS < 640V (80% of 800V). VBE16I07 VCE < 520V. VBC8338 VDS < 24V for a 28V system.
Current & Thermal Derating: Maximum junction temperature (Tj) should be derated to 110°C or lower for extended lifespan. Current ratings must be based on worst-case thermal impedance and ambient temperature profiles during hover (minimal cooling airflow).
III. Quantifiable Perspective on Scheme Advantages
Quantifiable Weight & Range Improvement: Utilizing the high-efficiency VBM18R20S in the propulsion inverter can reduce power loss by ~25% compared to standard 600V planar MOSFETs at the same current level. This directly reduces battery energy consumption, allowing for either extended relay mission time or increased payload (communication equipment) weight.
Quantifiable System Integration & Reliability Gain: Employing the VBC8338 for dual-channel management replaces at least four discrete components (two MOSFETs, two drivers), saving >60% PCB area and increasing the reliability (MTBF) of the power distribution network by reducing solder joints and component count.
Mission Availability Enhancement: The robust, derated design using carefully selected components like the VBE16I07 with its integrated FRD minimizes the risk of in-flight power system failures, maximizing the operational availability of the critical communication relay platform.
IV. Summary and Forward Look
This scheme establishes a robust, efficient, and integrated power chain for high-end eVTOL communication relays, addressing the unique demands of aerial mobility: high voltage for efficiency, intelligent power management for critical payloads, and uncompromising reliability.
Propulsion Level – Focus on "High-Voltage Efficiency": Leverage Super-Junction technology for the best trade-off in conduction and switching loss at high voltage, directly impacting the core metric of flight endurance.
Power Conversion Level – Focus on "Robust Simplicity": Employ proven IGBT+FRD solutions for mission-critical, medium-power converters where ruggedness and design simplicity are paramount.
Power Management Level – Focus on "Flexible Intelligence": Utilize highly integrated complementary MOSFET pairs to enable compact, feature-rich, and intelligent solid-state power distribution.
Future Evolution Directions:
Wide Bandgap (SiC/GaN) Adoption: For next-generation systems, the propulsion inverter (VBM18R20S role) would transition to a SiC MOSFET module, offering even higher efficiency, switching frequency, and power density. The DC-DC converter could utilize GaN HEMTs for ultra-compact, high-frequency design.
Fully Integrated Smart Power Switches: The auxiliary management would evolve towards Intelligent Power Switches (IPS) or e-fuses that integrate control, protection, and diagnostics, further simplifying the PDU and enabling predictive health monitoring.
This framework provides a foundational power device selection strategy. Engineers must refine it based on specific eVTOL parameters: propulsion motor voltage/power (e.g., 800V/250kW), communication payload power profile, thermal management architecture, and redundancy requirements.

Detailed Topology Diagrams