HP 3150 EN - Manual (Page 73)

EN ECU/power system 71
High-voltage power distribution
The high-voltage power supply PCA 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 ECU.
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 SW101 is open (in other words, when
the printer door is open).
Figure 10. High-voltage power supply circuit