Abstract: A piezoelectric acoustic transducer, especially for a printer photoreceptor toner transfer assist system, having a mechanical resonance varying over a substantial frequency range, is driven by a driver circuit having an automatically variable frequency electrical power output. The driver circuit initially automatically slowly sweeps over a wide frequency range encompassing the resonance range of the transducer until the resonant frequency is detected from the electrical impedance change of the transducer at resonance. The driver circuit then automatically switches to a frequency control with a phase lock loop system responsive to the phase of the transducer voltage and current, to hold and maintain the driver circuit output at the varying resonant frequency of the transducer. A small frequency range rapid dithering of the driver circuit frequency may be additionally provided above and below the resonant frequency of the transducer.

Abstract: Method and apparatus for providing multiple colors in a single pass of a copy sheet through a transfer station by switching the polarity of a transfer corotron and automatically adjusting the output of the detac corona device. In particular, a single power supply including high voltage switches responds to color selections to change the polarity of a transfer corotron to charge a copy sheet for toner transfer, and a current sense and precision rectifier stage responds to the copy sheet charge to provide a suitable detac charge independent of the transfer corotron polarity.