Canon NP6251 Service Manual page 126

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CHAPTER 4 IMAGE FORMATION SYSTEM

b. When the Primary Corona Current Output Is ON

HVTPC is less than about 11 V.

DCON is '1'.

Variable width pulse generator circuit goes ON.

Comparator circuit goes ON.

Drive circuit turns on.

Primary high-voltage transformer goes ON.

DC controller PCB

The above condition causes the high-voltage transformer to send high voltage suited

to the output of the primary charging level control signal (HVTPC) to the primary charging

If an excess corona current flows because of changes in the environment, the return

current to the comparator circuit increases, and the output decreases; this condition will

decrease the corona current from the primary charging assembly, controlling it to a

specific level at all times.

In photo mode, the target value is lowered by about 80 V than the dark area potential

) used in normal copying mode. As such, potential control is executed while making

the first copy in photo mode after power-on to control the primary corona current.

Comparator circuit

Figure 4-111

CANON NP6350/NP6251 REV. 0 JULY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON)

high-voltage

high-voltage

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