A wireless charging transmitter has a phase-shift controlled inverter, a capacitor, a transmitter coil, and a control circuit. The phase-shift controlled inverter has an input for receiving a phase-shift signal, and first and second output terminals for providing an inverter output voltage. The capacitor has a first terminal coupled to the first output terminal of the phase-shift controlled inverter, and a second terminal. The transmitter coil having a first terminal coupled to the second terminal of the capacitor, and a second terminal coupled to the second terminal of the phase-shift controlled inverter. The control circuit has an input coupled to the second terminal of the capacitor for sampling a capacitor voltage of the capacitor, and an output for providing the phase-shift signal corrected for the phase error. The control circuit determines the phase error of the capacitor voltage relative to a phase of an inverter output voltage to ensure the wireless charging transmitter operates in resonance.