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Q2431-90912 Chapter 5 Theory of operation 73
High-voltage circuit
The high-voltage circuit produces the voltage biases that are applied to the primary charging
roller, the developing cylinder, the transfer charging roller, and the pressure roller.
Figure 10. High-voltage circuit block diagram
The primary charging voltage (bias) applies a uniform negative charge to the photosensitive
drum in the print cartridge. There are two types of primary charging biases. The primary charging
dc negative voltage and the primary charging ac bias. Both biases are generated by the high-
voltage circuit on the power supply. These biases are superimposed on one another and then
applied to the primary charging roller which will transfer the biases to the drum. The laser/
scanner assembly generates the electrostatic image on the primary charged photosensitive
drum. See “Image formation system overview” on page 68. The electrostatic image cannot be
seen until toner is deposited on the drum.