Feature: Power electronics
power module that integrates transistors and gate drivers into a single compact package. T is drastically reduces loop inductance and eliminates layout-dependent switching behaviour typical of discrete MOSFET solutions.
GaN enables embedded drives Traditional silicon MOSFET motor drives usually operate at switching frequency of under 20kHz, as beyond that point switching losses rise quickly and thermal management becomes diffi cult. Humanoid robot joints, however, benefi t from operating at much higher PWM frequencies, about 80-100kHz. At these frequencies the current ripple is signifi cantly reduced, torque delivery becomes smoother, acoustic noise is greatly diminished and the control loop can run with higher bandwidth. An additional advantage is that the motor itself can be made smaller for the same performance. Gallium nitride (GaN) devices introduce a fundamentally
diff erent behaviour compared to silicon. T ey combine very fast switching speed with no reverse recovery charge. T is enables higher frequencies plus the elimination of the dead time required for a silicon MOSFET to recover from diode conduction. Because of this, GaN power stages can switch effi ciently around 100kHz whilst still keeping temperatures manageable inside a compact joint enclosure. T e much lower switching energy and extremely short dead times improve linearity and torque accuracy at low speed – a crucial requirement for precise robotic manipulation.
The EPC91122 evaluation board T e reference platform shown in Figure 2 is an example of an inverter that integrates a complete three-phase BLDC inverter
into a circular PCB intended for installation inside robotic joints. T e inverter core is a GaN three-phase power stage rated to 100V, integrating three half-bridges, gate drivers, bootstrap circuitry and level shiſt ing within a single compact package. T e board delivers phase current of up to 20Arms
(28A peak) and is typically operated
around 100kHz PWM with very short dead time, enabling low torque ripple and high control bandwidth. All functional subsystems required for a stand-alone servo drive
are included: the motor control microcontroller, magnetic rotor encoder interface (1024ppr class), phase current sensing, DC- bus voltage sensing, auxiliary 5V and 3.3V supplies and RS485 communication. T e inverter electronics occupies a space of 32mm inner diameter within a 55mm mechanical frame, reducing power loop inductance and improving dynamic response. T e wide input voltage range (approximately 10-65V) makes the
platform suitable for battery-powered robotics. Ceramic DC-link capacitors and short current paths allow fast current transients, whilst integrated protection and programming interfaces simplify fi rmware development and rapid evaluation in actuator prototypes.
Changed motor drive priorities Embedding the inverter inside the motor fundamentally changes motor drive design priorities. Power density, switching speed and integration replace traditional cabinet-level considerations. GaN technology enables this transition by combining low switching loss with high-frequency operation, making compact, effi cient joint actuators feasible. As humanoid robotics advances toward higher dexterity and
natural motion, highly integrated motor drives are likely to become the standard architecture, not an experimental approach.
Figure 2: Block diagram of the integrated architecture of the EPC91122 board
www.electronicsworld.co.uk April 2026 21
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