With the advancement of flexible automation, dual-arm collaborative robots have become core equipment for precision assembly and human-machine collaboration. The joint servo drive and safety control systems, serving as the "muscles and nerves" of the robot, provide dynamic power conversion and reliable safety isolation. The selection of power MOSFETs directly determines system power density, dynamic response, efficiency, and functional safety (SIL/PLe). Addressing the stringent requirements of cobots for compactness, high torque, safety, and reliability, 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 the dynamic and safety-critical operating conditions of cobots:
Sufficient Voltage Margin: For common 24V, 48V, and higher servo buses (e.g., 72V), reserve a rated voltage margin of ≥60-80% to handle regenerative braking voltage spikes and bus fluctuations. For 48V/72V joints, >100V rating is often necessary.
Prioritize Dynamic Loss & Power Density: Prioritize devices with ultra-low Rds(on) (reducing conduction loss in high continuous current) and optimized gate charge Qg (enabling high-frequency PWM for dynamic control). Compact, low-thermal-resistance packages are crucial for high power density in confined joint spaces.
Package & Thermal Matching: Choose packages like TO263, TO247, or advanced low-inductance modules for high-power joint drives, balancing current handling, thermal performance, and mounting area. Use compact SMD packages (SOP8, SOT23) for control and auxiliary circuits to save space.
Reliability & Safety Redundancy: Meet functional safety (SIL2/PLe) and continuous operation requirements. Focus on robust短路耐受能力, wide junction temperature range, and high avalanche energy rating for handling regenerative energy. Dedicated safety circuit MOSFETs require excellent stability and fail-safe characteristics.
(B) Scenario Adaptation Logic: Categorization by Function
Divide applications into three core scenarios: First, Joint Servo Motor Drive (Power & Dynamic Core), requiring high-current, high-efficiency, and bidirectional energy flow capability. Second, Safety & Brake Control (Safety-Critical), requiring fast, reliable switching for safe torque off (STO) and brake holding. Third, Auxiliary Power & Internal DC-DC Conversion (Functional Support), requiring compact, efficient power switching for controllers, sensors, and peripherals.
II. Detailed MOSFET Selection Scheme by Scenario
(A) Scenario 1: Joint Servo Motor Drive (48V/72V, 500W-2kW+) – Power & Dynamic Core Device
Joint drives require handling high continuous phase currents (tens of Amps) and significant peak currents during acceleration/deceleration, along with managing regenerative braking energy.
Recommended Model: VBL2406 (P-MOS, -40V, -110A, TO263)
Parameter Advantages: Trench technology achieves an extremely low Rds(on) of 4.1mΩ at 10V. Continuous current of -110A (peak much higher) is ideal for high-torque joint inverters on 24V/48V buses. The TO263 (D²PAK) package offers excellent thermal performance (low RthJC) and is suitable for direct mounting on busbars or heatsinks within joint modules.
Adaptation Value: Dramatically reduces conduction loss in inverter bridges. For a 48V/1kW joint (continuous phase current ~21A), per-device conduction loss can be below 0.18W. Enables high switching frequency (50-100kHz) for superior current loop control, enhancing dynamic response and reducing torque ripple. Its high current capability supports compact dual-inverter designs for two joints in one module.
Selection Notes: Verify maximum bus voltage (including regeneration) and phase current. Use in half-bridges with complementary N-MOSFETs (e.g., matched with similar Rds(on) N-channel devices). Implement rigorous thermal management with heatsinks. Pair with advanced gate drivers featuring desaturation detection for短路 protection.
(B) Scenario 2: Safety Torque Off (STO) & Brake Control – Safety-Critical Device
Safety circuits require fail-safe, high-side switching to cut off motor power and control holding brakes. Devices must have high voltage rating for safe isolation and low enough Rds(on) for minimal voltage drop.
Recommended Model: VBP2625 (P-MOS, -60V, -58A, TO247)
Parameter Advantages: -60V drain-source voltage provides strong margin for 24V/48V safety circuits. Rds(on) as low as 16mΩ at 10V ensures minimal power loss in the safety path. The robust TO247 package facilitates heatsinking for sustained brake holding current if needed. The -1.7V Vth allows for relatively straightforward gate control.
Adaptation Value: Enables reliable implementation of dual-channel STO circuits per ISO 13849-1, achieving PL e / SIL 2. Its low Rds(on) minimizes voltage sag to downstream circuits, ensuring brake coils receive full holding voltage. The independent device allows for physical isolation of safety paths from power paths.
Selection Notes: Use in conjunction with safety-certified logic and monitors to drive the gate. Implement redundancy (two in series) for higher safety integrity if required. Calculate worst-case dissipation during brake holding. Use a level-shift circuit (e.g., with NPN transistor) to drive this high-side P-MOS from low-voltage safety logic.
(C) Scenario 3: Internal DC-DC Power Conversion & Peripheral Switching – Functional Support Device
Internal power rails (12V, 5V, 3.3V) for controllers, sensors, and fans require efficient, compact, and low-noise switching conversion.
Recommended Model: VBA1108S (N-MOS, 100V, 15.5A, SOP8)
Parameter Advantages: 100V rating is ample for converting from 48V/72V buses. Low Rds(on) of 8mΩ at 10V maximizes efficiency in synchronous buck converters. The compact SOP8 package saves critical PCB space in the centralized controller box. Good balance of switching characteristics (Qg, Coss).
Adaptation Value: Serves as the perfect choice for the control FET or sync FET in non-isolated point-of-load (POL) buck converters. High efficiency reduces thermal load inside the enclosed control cabinet. Multiple devices can be used for independent switching of peripheral modules (fans, lights), enabling intelligent power management.
Selection Notes: Select based on the input voltage and output current of the target DC-DC stage. For high-frequency switching (>500kHz), pay attention to driver capability and loop layout to minimize ringing. A small local copper pour under the SOP8 package is sufficient for heat dissipation.
III. System-Level Design Implementation Points
(A) Drive Circuit Design: Matching Device Characteristics
VBL2406 (Joint Drive): Pair with high-current, high-speed gate drivers (e.g., 2A+ source/sink capability) with isolation and protection features. Optimize PCB layout for minimal power loop inductance. Use Kelvin source connections if possible. Implement active Miller clamp.
VBP2625 (Safety Control): Drive gate via a safety-monitored level-shift circuit. Include a strong pull-up resistor to ensure definite turn-off in case of control failure. Consider adding a small RC snubber across drain-source for noise immunity in long wiring to brakes.
VBA1108S (Power Conversion): Can be driven directly by many PWM controller outputs. Include a gate resistor (e.g., 2-10Ω) to control edge rates and minimize EMI. Ensure the driver supply is stable.
(B) Thermal Management Design: Tiered Strategy
VBL2406: Mount on a dedicated heatsink, possibly shared within the joint module. Use thermal interface material. Consider temperature monitoring via NTC on the heatsink.
VBP2625: Depending on brake holding duty cycle, may require a small heatsink or connection to a chassis thermal pad.
VBA1108S: Typically relies on PCB copper pour heat sinking. Ensure adequate copper area (≥150mm²) on top and bottom layers with thermal vias.
Overall: Design airflow (fan) in the control cabinet. Physically separate high-power joint drive MOSFETs from sensitive control circuitry.
(C) EMC and Reliability Assurance
EMC Suppression:
VBL2406: Use low-inductance busbar design for DC-link. Place high-frequency ceramic capacitors very close to inverter phase legs. Consider an output common-mode choke for motor cables.
VBP2625: Add a TVS diode at the drain terminal (to bus) for clamping voltage transients from long brake cable inductance.
General: Implement strict grounding and shielding. Use ferrite beads on auxiliary power outputs.
Reliability Protection:
Derating: Apply conservative derating (e.g., voltage ≤75%, current ≤60-70% at max operating temperature).
Overcurrent/Short-Circuit Protection: Essential for joint drives (VBL2406). Use desaturation detection in gate drivers or fast comparators with shunt resistors.
Overvoltage/Clamping: Size DC-link capacitors appropriately for regenerative energy. Consider an active clamp circuit or braking chopper for high-inertia loads.
ESD/Surge: Protect gate pins with TVS diodes or zeners, especially for externally accessible connections (safety circuits).
IV. Scheme Core Value and Optimization Suggestions
(A) Core Value
Maximized Power Density & Dynamics: Enables compact, high-torque joint designs with fast control bandwidth, improving robot speed and precision.
Safety and Performance Integrated: Dedicated safety-path MOSFETs enable certified functional safety without compromising main drive performance.
System-Level Efficiency: Low-loss devices across all scenarios minimize heat generation, reduce cooling demands, and extend component life.
Design Flexibility: The selected devices cover the full spectrum of cobot power needs, from µC to motor, with packages suited to their physical constraints.
(B) Optimization Suggestions
Higher Power/Voltage Joints: For >72V or higher power joints, consider VBP165R43SE (650V, 43A, SJ) or VBM15R30S (500V, 30A, SJ) for the inverter stage.
Space-Constrained Joints: For very compact modules, investigate using VBA2412 (P-MOS in SOP8) in lower-current auxiliary positions or complementary pair with VBA1108S.
Enhanced Safety Monitoring: For safety circuits, consider integrating current sensing (e.g., via shunt resistor) on the VBP2625 path for diagnostic feedback to the safety controller.
High-Voltage Auxiliary Supplies: For generating internal power from high-voltage buses (e.g., 400V), VBE155R02 (550V, 2A) could be used in specific low-power flyback converter topologies.
Conclusion
Power MOSFET selection is central to achieving the high power density, dynamic performance, and stringent safety required in dual-arm collaborative robots. This scenario-based scheme, from high-power joint drives to safety-critical isolation and efficient internal power management, provides comprehensive technical guidance for R&D through precise load matching and system-level design. Future exploration can focus on integrated power modules (IPMs) for joints and smart MOSFETs with embedded diagnostics, aiding in the development of next-generation, more intelligent, and compact cobots.

Detailed Topology Diagrams