Resonant load power supply with phase locked loop

Claim 1

In a power supply for delivering power to a resonant load comprising a vapor source work coil for inducing a current in a material to be vaporized and a capacitive element connected electrically in series with the coil: A. a voltage controlled oscillator for providing an output signal having a frequency determined by a control signal; B. means responsive to the oscillator signal for delivering power to the load at the frequency of the oscillator signal; C. a phase detector for monitoring the phases of the voltage delivered to the load and the voltage developed across the capacitive element and providing output signals corresponding to the relative phases of sAid voltages; D. means responsive to the phase detector output signals for providing a signal having an average magnitude corresponding to the relative phases of the voltage delivered to the load and the voltage across the capacitive element; and E. means for comparing the average magnitude of the last named signal with a reference signal having a level corresponding to a predetermined difference in the monitored phases and varying the voltage of the control signal applied to the oscillator in accordance with deviations of the average magnitude from the level of the reference signal to maintain the oscillator signal at a predetermined frequency.