Primary charge The primary charge roller applies a negative DC bias to the drum. To maintain a consistent charge across the drum’s surface, an AC bias is also applied. The charge voltage on the drum surface ranges from approximately -700 V to -500 V. With the large negative charge on the drum surface, an equal positive charge forms below the photoconductive material. Figure 5-3 Primary charge C7085-90921 Chapter 5 Theory of operation 105