| 摘要 |
<p>A dual feedback control system for a Class-D power circuit maximizes efficiency by controlling the magnitude and phase angle of the resonant load circuit using two separate feedback loops. The first feedback loop 40 changes the value of a first variable capacitor in response to difference in magnitude between the actual load impedance and the desired load impedance. The second feedback loop 30 changes the value of a second variable capacitor in response to the phase difference between the actual phase angle and the desired phase angle. In this way, the real and imaginary components of the load impedance are controlled so that the Class-D circuit is in tune, and hence efficiency is maximized, over a wide range of load impedances. The dual feedback control of the present invention may be advantageously employed in the ballast of an electrodeless HID lamp system. <IMAGE></p> |
