Toshiba e-studio550 Service Manual page 155

10. 5. Surface Potential Sensor
10. 5. 1. General description
The surface potential sensor detects the surface potential of the photoconductive drum and controls it
to keep constant.
10. 5. 2. Construction
The surface potential is controlled by the following construction.
• Surface potential sensor
• Control section
• High-voltage transformer
Main charger grid
Surface potential sensor
Photo-
conductive
drum
10. 5. 3. Control method
(1) Surface potential correction control
The adjusted output value of the main grid voltage in the BC-RAM is output to the main CPU.
Then control voltage data is output to the D/A converter from the main CPU through the gate
array.
The data is converted into the analog data by the D/A converter and then amplified.
The control voltage of the main output is output to the high-voltage transformer.
The high-voltage transformer outputs the main grid voltage proportionate to the control voltage.
The surface potential sensor detects the potential on the photoconductive drum and gives it
feedback to the main CPU.
The potential is compared to the control allowable level specified in the BC-RAM.
If the potential is out of the control allowable level, the main grid voltage to be changed is
calculated from the difference between the targeted value and detection value.
The output value of the main grid voltage is changed.
e-STUDIO550/650/810 PROCESS RELATED SECTION
: Detecting the surface potential of the photoconductive drum
: Controlling to keep the surface potential constant
: Supplying voltage to the main charger grid
Control
voltage
signal
High-voltage
transformer
D/A converter
IC18
10 - 6
PWA-F-LGC-340/341/342
Gate
Main CPU
array
IC58
IC56
BC-RAM
IC27
JUNE 2002 © TOSHIBA TEC