With the advancement of industrial automation and flexible manufacturing, collaborative robot (cobot) clusters have become core components of intelligent production lines. The power delivery and motor drive systems, serving as the "power source and motion executor" of each cobot unit, provide precise power conversion and control for key loads such as joint servo motors, control logic circuits, and safety brake modules. The selection of power MOSFETs directly determines system efficiency, dynamic response, power density, and operational reliability. Addressing the stringent requirements of cobot clusters for safety, precision, high duty cycles, and compact integration, this article focuses on scenario-based adaptation to develop a practical and optimized MOSFET selection strategy.
I. Core Selection Principles and Scenario Adaptation Logic
(A) Core Selection Principles: Four-Dimensional Collaborative Adaptation
MOSFET selection requires coordinated adaptation across four dimensions—voltage, loss, package, and reliability—ensuring precise matching with system operating conditions:
Sufficient Voltage Margin: For common DC bus voltages (24V, 48V, 72V, or higher), reserve a rated voltage withstand margin of ≥50-100% to handle regenerative braking spikes, bus fluctuations, and inductive kickback. For example, prioritize devices with ≥100V for a 48V bus.
Prioritize Dynamic Performance & Low Loss: Prioritize devices with very low Rds(on) (minimizing conduction loss in high-current paths), and optimized Qg & Coss (enabling fast switching for PWM control), adapting to frequent start-stop and torque control cycles, improving energy efficiency, and reducing thermal stress.
Package & Power Matching: Choose low-inductance, low-thermal-resistance packages like TO-263-7L or TO-247 for high-power joint motor drives. Select compact packages like TO-251 or DFN for medium/small power auxiliary circuits (logic, fans, sensors) or safety modules, balancing power density and thermal management.
Reliability Redundancy: Meet high duty cycle and 24/7 operational demands, focusing on robust thermal performance, avalanche energy rating, and wide junction temperature range (e.g., -55°C ~ 150°C or 175°C), adapting to the harsh industrial environment.
(B) Scenario Adaptation Logic: Categorization by System Function
Divide loads into three core scenarios based on function within the cobot cluster: First, Joint Servo Motor Drive (Power & Motion Core), requiring high-current, high-efficiency, and fast-switching capability for precise torque control. Second, Auxiliary & Control Power Management (Functional Support), requiring efficient power distribution and switching for controllers, sensors, and communication. Third, Safety & Brake Control (Safety-Critical), requiring reliable high-side switching for safety brakes and isolation functions to ensure functional safety (SIL/PL). This enables precise parameter-to-need matching.
II. Detailed MOSFET Selection Scheme by Scenario
(A) Scenario 1: Joint Servo Motor Drive (500W-2kW+) – Power & Motion Core Device
Joint servo drives require handling high continuous and peak currents (during acceleration/deceleration), demanding extremely low conduction loss and excellent dynamic switching for high-frequency PWM control.
Recommended Model: VBGL71203 (N-MOS, 120V, 190A, TO-263-7L)
Parameter Advantages: SGT (Shielded Gate Trench) technology achieves an ultra-low Rds(on) of 2.8mΩ at 10V. Extremely high continuous current of 190A suits 48V/72V+ bus systems common in cobots. TO-263-7L package offers excellent thermal performance and low parasitic inductance, crucial for heat dissipation in confined spaces and minimizing switching voltage spikes.
Adaptation Value: Drastically reduces conduction loss in motor phase legs. For a 48V/1kW servo drive (~21A RMS phase current), conduction loss per device is minimal, enabling drive efficiency >97%. Supports high-frequency PWM (tens of kHz), essential for smooth, low-noise motor operation and precise current loop control, meeting high dynamic response requirements.
Selection Notes: Verify motor peak current and bus voltage during regenerative braking. Ensure sufficient PCB copper area (≥300mm²) and thermal vias for heat sinking. Must be paired with high-performance gate drivers (e.g., with >2A source/sink capability) and include comprehensive protection (overcurrent, overtemperature, shoot-through).
(B) Scenario 2: Auxiliary & Control Power Distribution – Functional Support Device
Auxiliary loads (Controller MCU/MPU, sensors, network switches, cooling fans) are medium-to-low power but critical for operation, requiring efficient switching and compact size.
Recommended Model: VBFB1311 (N-MOS, 30V, 50A, TO-251)
Parameter Advantages: 30V withstand voltage is ideal for 12V/24V control buses. Very low Rds(on) of 7mΩ at 10V minimizes voltage drop and loss. TO-251 package offers a good balance of power handling and space savings. Low Vth of 1.7V allows for direct or easy drive by 3.3V/5V logic.
Adaptation Value: Enables efficient power gating for various subsystems, reducing standby power and managing inrush currents. Suitable for point-of-load (POL) switching, fan speed control, or as a high-side switch for sensor clusters. Its low loss improves overall system efficiency.
Selection Notes: Keep load current well below the 50A rating for thermal headroom. Add appropriate gate resistors to control slew rate and prevent oscillation. Consider parallel use for higher current auxiliary rails.
(C) Scenario 3: Safety Brake Control & High-Voltage Management – Safety-Critical Device
Safety brakes (holding brakes on servo motors) and certain high-voltage auxiliary supplies require absolutely reliable switching for functional safety. Devices must handle potentially high voltages and provide robust isolation.
Recommended Model: VBP165R18 (N-MOS, 650V, 18A, TO-247)
Parameter Advantages: High 650V drain-source voltage rating is suitable for direct switching on rectified high-line AC inputs (e.g., 400VAC bus) or as a main disconnect switch. TO-247 package provides superior thermal dissipation capability for sustained power handling. Planar technology offers proven robustness and stability.
Adaptation Value: Can be used as a robust high-side switch for 400VAC/240VAC safety brake coils, ensuring reliable engagement/disengagement during E-Stop or power loss. Also suitable for pre-charge circuits or as a main power switch in cluster power distribution units (PDUs). Its high voltage rating provides significant margin for surge events.
Selection Notes: Critical for safety circuits; implement with redundancy (e.g., two in series) where required by safety standards. Use isolated gate drivers (e.g., photocoupler or capacitive isolator-based) for high-side switching. Incorporate snubber circuits to manage inductive switching of brake coils. Ensure thorough derating on current at maximum operating temperature.
III. System-Level Design Implementation Points
(A) Drive Circuit Design: Matching Device Characteristics
VBGL71203: Pair with high-current, high-speed gate driver ICs (e.g., UCC5350, ISL8117) capable of fast transitions. Minimize power loop inductance with a tight PCB layout. Use Kelvin source connections if available. Implement active Miller clamp or gate resistor tuning to prevent parasitic turn-on.
VBFB1311: Can often be driven directly by microcontroller GPIOs through a small series resistor. For faster switching or driving multiple in parallel, use a dedicated logic-level gate driver.
VBP165R18: For high-side switching, mandatory use of isolated gate drivers. Include appropriate pull-down/pull-up resistors on the gate. Implement RC snubbers across the drain-source for inductive loads like brake coils.
(B) Thermal Management Design: Tiered Heat Dissipation
VBGL71203 (TO-263-7L): Requires significant PCB copper area (≥300mm², 2oz+ recommended) with abundant thermal vias to an internal ground plane or dedicated thermal layer. For high-power joints, consider mounting on a heatsink attached to the robot arm's structure or a dedicated cold plate in the base.
VBFB1311 (TO-251): Local copper pour (≥100mm²) is typically sufficient. In dense clusters of these devices, ensure adequate airflow.
VBP165R18 (TO-247): Designed for heatsink mounting. Use thermally conductive pads or grease and secure to a chassis-mounted heatsink, especially when used in PDU applications. Ensure heatsink sizing accounts for worst-case dissipation.
(C) EMC and Reliability Assurance
EMC Suppression:
VBGL71203: Use low-ESR/ESL ceramic capacitors very close to drain and source pins. Implement ferrite beads or common-mode chokes on motor cables. Ensure shielded motor cables are properly grounded.
General: Implement strict PCB zoning (power, analog, digital). Use EMI filters at all power entry points. Add snubbers across switching nodes where needed.
Reliability Protection:
Derating Design: Apply conservative derating (e.g., 60-70% of max current rating at max expected case temperature).
Overcurrent/Overtemperature Protection: Implement phase current sensing with fast comparators for motor drives. Use drivers with integrated fault reporting. Include NTC thermistors on critical heatsinks.
Voltage Transient Protection: Use TVS diodes or varistors on DC bus inputs to clamp regenerative and surge voltages. Use RC snubbers or avalanche-rated MOSFETs to handle inductive energy.
IV. Scheme Core Value and Optimization Suggestions
(A) Core Value
High Dynamic Response & Efficiency: Ultra-low Rds(on) and optimized switching devices enable high-efficiency motor drives (>97%), reducing energy costs and heat generation, allowing for higher power density in compact joints.
Enhanced Safety & Reliability: Dedicated high-voltage robust devices for safety-critical functions help meet functional safety (SIL/PL) requirements. The selected devices offer thermal and electrical margins for 24/7 operation.
Scalability for Cluster Architecture: The device portfolio covers from high-power joints to low-power control, supporting a scalable design approach for cobots of different sizes and cluster configurations.
(B) Optimization Suggestions
Power Scaling: For very high-power cobot joints (>3kW), consider paralleling VBGL71203 or exploring higher current modules. For lower-power 6-axis cobots, VBM1202M (200V/14A, TO-220) could be an alternative for joint drives.
Integration Upgrade: For space-constrained joint drives, consider using integrated power modules (IPMs). For advanced safety circuits requiring monitoring, look for MOSFETs with integrated sense FETs or temperature sensing.
Specialized Scenarios: For cobots operating in high-vibration environments, ensure proper mechanical fixation of TO-247/TO-220 packages. For extremely compact modules, VBQA2104N (P-MOS, -100V, -28A, DFN8) could be evaluated for high-side switching in tight spaces, though drive complexity increases.
Conclusion
Power MOSFET selection is central to achieving high efficiency, dynamic performance, safety, and reliability in collaborative robot cluster drive and power systems. This scenario-based scheme provides comprehensive technical guidance for R&D through precise load matching and system-level design. Future exploration can focus on Wide Bandgap (SiC/GaN) devices for ultra-high efficiency and switching frequency, as well as smarter, monitored power stages, aiding in the development of next-generation, high-performance cobot clusters for the smart factory.

Detailed MOSFET Application Topology Diagrams