A surgical instrument includes a shaft, an ultrasonic transducer, a waveguide acoustically coupled with the ultrasonic transducer and extending distally through the shaft, and an end effector arranged at a distal end of the shaft. The end effector includes an ultrasonic blade acoustically coupled with the waveguide, a clamp arm movable relative to the ultrasonic blade for clamping tissue, and an RF electrode operable to seal tissue with RF energy. The ultrasonic transducer is operable to drive the waveguide and the ultrasonic blade with ultrasonic energy. The surgical instrument further includes an ultrasonic electrical circuit operable to energize the ultrasonic transducer, and an RF electrical circuit operable to deliver RF energy to the RF electrode. A return path of the ultrasonic electrical circuit and a return path of the RF electrical circuit pass through a shared electrically conductive element.