Preface: Architecting the "Power Heart" for Aerial Mobility Resilience – Discussing the Systems Thinking Behind Power Device Selection for eVTOLs
In the rapidly evolving domain of advanced air mobility (AAM) and specifically for electric vertical take-off and landing (eVTOL) vehicles equipped with low-altitude emergency power supply systems, exceptional performance is defined not just by energy storage capacity but by an intelligent, robust, and ultra-efficient electrical power "distribution and conversion network." Core metrics—such as peak thrust-to-weight ratio for safe landing, high-efficiency energy transfer during emergency mode, and flawless operation of avionics and critical flight systems—are fundamentally anchored in the selection and integration of power semiconductor devices. This article adopts a holistic, mission-critical design philosophy to address the core challenges within the eVTOL emergency power chain: how to select the optimal power MOSFETs under extreme constraints of unparalleled power density, ultimate reliability under thermal cycling, harsh operational environments (vibration, altitude), and stringent safety mandates, focusing on three key nodes: high-power main propulsion inversion, high-voltage DC conversion for emergency systems, and critical auxiliary load management.
I. In-Depth Analysis of the Selected Device Combination and Application Roles
1. The Thrust Workhorse: VBP1151N (150V, 150A, TO-247) – Main Propulsion Inverter Low-Side Switch
Core Positioning & System Imperative: As the primary switch in the multi-phase inverter bridges driving high-torque lift/cruise motors, its ultra-low Rds(on) of 12mΩ @10V is paramount. During critical flight phases like takeoff, landing, or emergency power engagement, minimizing conduction loss translates directly to:
Maximized Available Thrust & Hover Time: Preserves precious onboard energy, extending the window for safe landing under emergency power.
Uncompromised Peak Power Delivery: The low Rds(on) combined with the robust TO-247 package and trench technology ensures handling of extreme transient currents (refer to SOA), meeting the instantaneous high-torque demands of multi-rotor systems.
Thermal Management Simplification: Reduced losses lower the thermal burden on the often liquid-cooled inverter system, enhancing reliability and potentially reducing cooling system weight and complexity.
Drive & Layout Considerations: Its high current rating and low Rds(on) necessitate a dedicated, low-inductance gate drive circuit capable of rapid switching to manage switching losses at high PWM frequencies essential for motor control bandwidth.
2. The High-Voltage Energy Bridge: VBL16R25SFD (600V, 25A, TO-263) – Isolated High-Voltage DCDC Converter Switch for Emergency System
Core Positioning & Topology Fit: Ideal for the critical power conversion stage linking the primary high-voltage battery bus (e.g., 400V-500V) to a dedicated, isolated emergency power bus or for bidirectional transfer in hybrid storage systems. The 600V rating provides robust margin for voltage transients. The Super-Junction Multi-EPI technology offers an excellent balance between low switching loss and low conduction loss.
Key Technical Parameter Analysis:
Efficiency at Medium Frequency: With Rds(on) of 120mΩ, it maintains low conduction loss for its current class. The SJ technology enables efficient operation at elevated switching frequencies (e.g., 50kHz-100kHz), allowing for smaller magnetics in the isolation transformer—a critical advantage for weight-sensitive aerospace applications.
Avalanche Ruggedness: Devices like these often specify avalanche energy capability, a vital feature for handling inductive energy from transformer leakage inductance during fault conditions or hard switching, enhancing system-level reliability.
Selection Rationale: Chosen over lower-voltage or planar MOSFETs for its combination of sufficient current handling, high voltage blocking capability, and good switching performance, making it a cornerstone for compact, efficient, and safe high-voltage power conversion in emergency scenarios.
3. The Critical Systems Guardian: VBM1202N (200V, 80A, TO-220) – High-Current Auxiliary & Critical Load Switch
Core Positioning & System Integration: This device serves as the robust switch for managing high-power, mission-critical auxiliary systems in an eVTOL, such as flight control hydraulics/pneumatics, emergency lighting, or communication backup power. Its 200V rating is suitable for 48V or higher auxiliary bus systems common in aviation.
Application Example: Enables rapid, controlled power shedding of non-essential loads during emergency power mode or provides solid-state switching for redundant power paths to critical avionics.
Performance Justification: The 17mΩ Rds(on) ensures minimal voltage drop and power loss even when conducting high continuous currents, crucial for maintaining voltage stability for sensitive avionics. The TO-220 package offers a good balance of current capability and mounting flexibility for board or heatsink attachment.
Drive Considerations: As an N-channel MOSFET used as a high-side switch, it requires a dedicated gate driver or charge pump circuit. This investment is justified for channels where low conduction loss and high reliability outweigh the simplicity of a P-channel solution.
II. System Integration Design and Expanded Key Considerations
1. Topology, Drive, and Control Loop Synergy
Propulsion Inverter & Motor Controller: The VBP1151N switches must be driven by high-performance, isolated gate drivers tightly synchronized with the motor controller's FOC algorithm. Switching symmetry is critical for minimizing torque ripple and acoustic noise.
High-Voltage DCDC Control: The VBL16R25SFD operates within a tightly regulated voltage control loop, often using phase-shifted full-bridge or LLC topologies for high efficiency. Its driver must be immune to high common-mode transients.
Intelligent Power Distribution: The VBM1202N is controlled by the Vehicle Management Computer (VMC) or a dedicated Power Distribution Unit (PDU), implementing sequenced startup, load monitoring, and ultra-fast fault isolation based on current sensing.
2. Hierarchical and Aggressive Thermal Management
Primary Heat Source (Liquid Cold Plate): The VBP1151N in the propulsion inverter is the highest power dissipation element, requiring direct mounting onto a liquid-cooled cold plate with optimized thermal interface material.
Secondary Heat Source (Forced Air/Conduction): The VBL16R25SFD within the DCDC module may be cooled via a dedicated heatsink coupled to forced air flow or via thermal conduction to the module's baseplate.
Tertiary Heat Source (PCB/Chassis Conduction): The VBM1202N, while handling significant current, can often be managed through a carefully designed PCB with thick copper layers, thermal vias, and attachment to the airframe chassis for heat spreading.
3. Engineering for Aerospace-Grade Reliability
Electrical Stress & Protection:
VBL16R25SFD: Requires snubber networks to clamp voltage spikes from transformer leakage inductance. Careful attention to PCB layout to minimize parasitic inductance in the power loop is non-negotiable.
Inductive Load Switching (VBM1202N): Each critical inductive load must have appropriate flyback or clamp circuits (TVS, RCD) to absorb turn-off energy and protect the switch.
Gate Drive Fortification: All gate drives require protection against overvoltage (zeners), undervoltage lockout, and include sufficient pull-down resistance. Design must account for potential single-event effects (SEE) in high-altitude applications.
Derating Practice (Stringent):
Voltage Derating: Operational VDS for VBL16R25SFD should not exceed 70-80% of 600V (420V-480V) under worst-case transients. Similarly, margins are applied to other devices.
Current & Thermal Derating: Maximum junction temperature (Tjmax) should be derated significantly (e.g., Tj < 110°C for a 150°C rated part) to ensure long-term reliability. Current ratings are based on actual worst-case thermal impedance and heatsink temperatures.
III. Quantifiable Perspective on Scheme Advantages
Quantifiable Thrust Efficiency: For a 200kW peak propulsion system, employing VBP1151N with its ultra-low Rds(on) can reduce inverter conduction losses by over 25% compared to standard 150V MOSFETs, directly increasing hover endurance or allowing for battery weight reduction.
Quantifiable Power Density: The use of VBL16R25SFD (SJ technology) in the high-voltage DCDC enables higher switching frequencies, potentially reducing transformer size and weight by 30-40% compared to designs using planar MOSFETs at lower frequencies—a critical gain in aerospace.
Quantifiable System Reliability: Implementing robust switches like VBM1202N for critical load management, with proper protection, reduces the probability of failure for essential systems, directly contributing to a higher system-level MTBF and enhanced vehicle safety.
IV. Summary and Forward Look
This selection provides a robust, optimized power chain backbone for eVTOL emergency power systems, addressing the high-stakes requirements from megawatt-level propulsion to kilowatt-level critical system management.
Energy Conversion Level – Focus on "High-Density Efficiency": Select Super-Junction technology for high-voltage conversion where switching loss and weight are paramount.
Power Output Level – Focus on "Ultimate Current Handling": Employ trench technology MOSFETs with the lowest possible Rds(on) in the propulsion path, where conduction loss dominates.
Power Management Level – Focus on "Robust Critical Control": Utilize high-current, reliable switches for ensuring power availability to systems essential for safe flight and landing.
Future Evolution Directions:
Wide Bandgap Adoption: Transitioning the main inverter to Gallium Nitride (GaN) HEMTs could offer even higher switching frequencies and efficiency, further reducing motor filter size and weight.
Fully Integrated Smart Power Nodes: Adoption of Intelligent Power Switches (IPS) with embedded diagnostics, current sensing, and communication (e.g., PMBus) for auxiliary loads would enable predictive health monitoring and simplify wiring harnesses.
Engineers must refine this framework based on specific eVTOL parameters: propulsion voltage (e.g., 800V), emergency power architecture, detailed load profiles, and the most stringent thermal and environmental (DO-160) requirements to achieve a certifiable, high-performance power system.

Detailed Topology Diagrams