High-voltage power distribution The high-voltage power supply applies an overlap of DC and AC voltage to the primary charging roller and the developing roller. This circuit also applies a positive or negative DC voltage to the transfer roller according to the instructions from the engine control unit. This circuit also controls the image density by changing the primary AC voltage and the developing AC bias according to the print density setting. High voltage is disabled when the printer door is open. Figure 15. High-voltage power supply circuit ENWW Printer functions 63