Digital control and active tuning for a wireless charger of an implantable medical device

An external charger configured for charging a battery of an implantable medical device, the external charger comprising:

• a transmission coil configured for generating a time-varying magnetic field with a driving frequency;
• an electrical circuit for providing an alternating current (AC) waveform to the transmission coil, wherein providing the AC waveform to the transmission coil causes the transmission coil to generate the time-varying magnetic field, the electrical circuit having a resonant frequency;
• one or more capacitors;
• one or more switches configured to switch the one or more capacitors into the electrical circuit;
• and
• a controller configured for controlling the one or more switches to switch the one or more capacitors into the circuit to maintain the resonant frequency of the circuit equal to the driving frequency.