D. Controlling the Separation/Pre-Transfer Corona Current
1. Outline
Figure 4-113 shows the circuit used to control the separation corona current and the
pre-transfer corona current, and the circuit has the following functions:
q
Turning on and off the separation/pre-transfer corona current.
w
Switching the separation corona current level.
e
Controlling the separation corona current to a specific level.
r
Switching the pre-transfer corona current level.
t
Controlling the re-transfer corona current to a specific level.
The DC component of the separation charging assembly and the pre-transfer
charging assembly is controlled to a specific current by obtaining a sampling signal from
the secondary side of the high-voltage transformer (HVT) with the aim of eliminating the
effects of changes in the environment on corona charging. (The AC transformer is
controlled to a specific voltage.)
The separation corona current is varied to eliminate the effects of changes in the
environment by measuring the surface potential of the drum and in relation to the output
of the environment sensor.
Figure 4-113
+
- -
+
- -
DC controller PCB
HVT.POST.AC
HVT.POST.DC
Q156
D/A converter
ROED
J114
A-7
DCON
J202
-4
J114
A-1
J202
-10
J114
A-10
J202
-1
J114
A-8
J202
-3
J114
A-9
J202
-2
HVSCT
HVTOFF
Switching
circuit
AC control
circuit
Constant
current
control circuit
Drive
circuit
Drive
circuit
(HVT)
Overcurrent
detection
circuit
Switching
circuit
Constant
current control
circuit
Drive
circuit
DC transformerT302
DC transformerT402
(positive power supply)
DC transformerT301
(negative power supply)
AC transformerT201
Photosensitive drum
Microprocessor (master)
Switching
circuit
Switching
circuit
COPYRIGHT © 1997 CANON INC. CANON NP6350/NP6251 REV. 0 JULY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON)
CHAPTER 4 IMAGE FORMATION SYSTEM
4-15