This specification describes a device that includes a voltage-regulated DC-DC converter comprising a switching network, a resonant circuit, and control circuitry, wherein the switching network has a switching frequency. The DC-DC converter has an output impedance and the control circuity uses a control loop to control the DC-DC converter. The control circuitry implements the control loop using: an output voltage sensor configured to sense an output voltage of the DC-DC converter; and a compensator configured to adjust operation of the DC-DC converter based on the output voltage sensed by the output voltage sensor. The DC-DC converter comprises an output impedance suppression mechanism configured to at least partially suppress increases in the output impedance of the DC-DC converter.