Abstract: An electronic ballast has a resonant tank circuit that includes a tank inductor and a tank capacitor connected in series. Lossless sampling of the output voltage of the electronic ballast is achieved by monitoring the voltage across a sampling capacitor placed in series with the tank capacitor. A resistive and capacitive filter is used to filter the monitored voltage such that it can be accurately received by a microcontroller. A resistor is connected in series with the sampling capacitor to produce an open circuit output voltage control signal that is used by the microcontroller to limit the open circuit output voltage. A cable compensation circuit is utilized to minimize variations in the open circuit voltage due to the connecting and disconnecting of a cable to the ballast output terminals. 17.

Abstract: An electronic ballast uses a voltage sampling circuit and a voltage control circuit to limit the open circuit voltage of the ballast. A lamp voltage sensing circuit is provided that uses a voltage dividing capacitor to accomplish lossless monitoring of the open circuit voltage of the ballast. A resistor placed in series with the sampling capacitor is used to create a voltage that turns a control transistor off and on. The control transistor produces a gating signal trimming signal that a half bridge driver uses to alter the gating signals provided to the inverter transistors of the ballast. A cable compensation circuit is included that minimizes variations in the open circuit voltage due to the connecting and disconnecting of a cable to the ballast by turning the control transistor off and on.