Canon NP6085 Service Manual page 121

D. Controlling the Primary/ Transfer
Corona Current
1. Outline
Figure 3-316 shows the circuit that controls the
primary/transfer corona, and the circuit has the
following functions:
1 Turns ON and OFF the primary corona current.
2 Controls the primary corona current to a con-
stant level.
3 Turns ON and OFF the transfer corona current.
4 Switching the transfer corona current level.
2. Controlling the Primary Corona Current
The DC controller PCB compares the drum
surface potential V
D
detection circuit against the target potential; if
there is a difference, it corrects the signals used
to control the primary corona current it generates.
The corrected signals are converted into analog
signals (HVTPC signals) by the D/A converter cir-
cuit and sent to the high-voltage transformer,
thereby controlling the primary corona current.
CP101
-1
Q158
Micro-
processor
CP101
-2
D/A converter
circuit
DC controller PCB
COPYRIGHT © 1996 CANON INC.
obtained by the potential
J127 J721
-B2
-4
HVTPC
Differential
amplifier
J127
J721
circuit
HVRMT
-7
B6
Switching
J721
J127
HVTCT
-3
-B1
Differential
amplifier circuit
J721
-5
HVRMT
Switching
CANON NP6085 REV.0 JULY 1996 PRINTED IN JAPAN (IMPRIME AU JAPON)
The primary corona current output is turned
ON and OFF by the high-voltage remote signal
(HVRMT) and is controlled by the HVTPC signal.
When the HVTPC signal is about 8 V or more
and less than 16 V, the primary corona current
turns ON; it turns OFF when the output is about
16 V or more.
a. Turning the Primary Corona Current Output
HVTPC is about 16 V or more.
HVRMT is '1'.
The differential amplifier circuit turns OFF.
The primary high-voltage transformer
turns OFF.
b. Turning ON the Primary Corona Current
Output
HVTPC is less than 16 V.
HVRMT is '0'.
The differential amplifier circuit turns ON.
The primary high-voltage transformer
turns ON.
Current
Variable pulse
+ --
amplifier
width oscillator
circuit
circuit
High-voltage transformer
circuit
Current
Variable pulse
+ --
amplifier
width oscillator
circuit
circuit
High-voltage transformer
circuit
High-voltage transformer (HVT1)
Figure 3-316
3. OPERATIONS AND TIMING
for primary current
for transformer
Primary charging
assembly
Photo-
sensitive
drum
Transfer charging
assembly
3-63