Litz wire battery powered device

A medical instrument comprising:

• a battery operated radio frequency (RF) generation circuit operable to generate an RF drive signal and to provide the RF drive signal to the at least one electrical contact;
• and
• a control circuit configured to vary the duty cycle of the RF drive signal;
• and
• a sampling circuit coupled to the control circuit;
• wherein the RF generation circuit comprises a resonant circuit comprising at least one inductive element constructed of litz wire;
• wherein the control circuit is operable to receive a measurement of the RF drive signal and from the sampling circuit and is operable to vary the frequency of the RF drive signal to control the power, voltage and/or current delivered to at least one electrical contact of the end effector;
• and
• wherein the sampling circuit is configured to sample a sensed voltage or current signal at a sampling frequency that varies in synchronism with the frequency and phase of the RF drive signal.