electrostatic image on the primary charged photosensitive drum. See Image-formation system. The
electrostatic image cannot be seen until toner is deposited on the drum.
The developing voltage (bias) causes the toner to adhere to the electrostatic image that the laser/
scanner assembly created on the photosensitive drum. Two types of developing biases are used: the
developing dc negative bias and the developing ac bias. The high-voltage circuit on the power supply
generates both biases. These biases are superimposed on one another and then applied to the
primary charging roller, which transfers the biases to the drum. The biased developing cylinder picks
up toner particles and deposits them onto the electrostatic image on the photosensitive drum. The
image is now visible on the drum.
The transfer voltage (bias) transfers the toner image on the photosensitive drum to the media. Two
types of developing biases are used: the transfer dc positive bias and the dc negative bias. The high-
voltage circuit on the power supply generates both biases. Transfer dc positive bias is applied to the
transfer roller during the toner-transfer process. Transfer dc positive bias is applied to the transfer
roller during the transfer-roller cleaning process. The dc positive bias attracts the toner to the media
(this transfers the toner image on the photosensitive drum to the media). This bias is weakened
between pages to prevent residual toner that is on the photosensitive drum from adhering to the
transfer-charging roller when media is not present. The dc-negative bias is used to clean residual
toner off of the transfer roller.
The fuser pressure-roller voltage (bias) prevents toner on the media from sticking to the fuser’s
pressure roller. The pressure-roller bias is dc-positive.
The fuser-sleeve voltage (bias) prevents toner on the media from sticking to the fuser sleeve. The
fuser-sleeve bias is dc-negative.
Low-voltage power supply
The low-voltage circuit converts the ac power from the power source into the direct current voltage
(Vdc) that the MFP components use. The low-voltage power supply circuit has three components:
■ The power-factor controller power supply converts the ac voltage to dc voltage.
■ The engine power supply generates the +24 Vdc that the high-voltage power supply requires.
■ The dc controller generates the +5 Vdc that the laser/scanner and formatter require, and the
+3.3 Vdc that the sensors and control-panel require.
Figure 5-6 Low-voltage power supply circuit illustrates the low-voltage power supply circuit.
92 5 Theory of operation
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