Canon Canovision8 E50E Service Manual page 171

3.
Constant Voltage Circuit (in Adapter mode)
In adapter mode, C terminal goes high to turn off 031 and 32. Zener voltage at ZD27 is divided by
R42 and 44 and it is applied to (+) side of comparator 1 as a reference voltage. On the other hand, the
voltage at output terminal (+) is divided by R45, 46 and VR21 and applied to the {~) side via R43 to be
compared. :
tf the output voltage rises, it is regutated in the following manner.
* Output voltage rises (reference voltage for comparator 1) > Output of comparator decreased > Current
(emission) of PHC-1 diode increased > Potential at pin.10 of IC51 decreased > High period of output at
pin 2 of ICS51 shortened > ON period at Q1 shortened > Drop of output voltage to constant level.
When the output voltage drops, it is raised to a constant voltage. by reversing the above procedures.
In adapter mode, the comparator 2 regulates the excessive current. Zener voltage at ZD21 is divided
by R31 and. 32 and it is applied to the (+) side as a reference voltage. On the other hand, to the (-)
side, the voltage at R22 and TF21 is applied to be compared. In this manner, the comparator 2 limits
the current usually to 1.5A. However, the current which flows instantaneously is limited to 2.5A.
(ex.: The rush current at the motor starting)
Constant Current Circuit (in charge mode)
CA-E7 regulates the charging current to 1.1A (maximum voltage: 11.0V approx.).
In charge mode, C terminal goes low to turn on Q31 and 32. R33 is connected between the (+) side
of comparator 2 and ground via Q31 and then the potential drops. The charging current is converted into
voltage by R22 and. TF21 and then applied to the {-) side to be compared. On the other hand, to the (+)
side of comparator 1, 032, D32 and R40 are applied in parallel so that the reference voltage at the
comparator 1 goes high, Sais
The state of output at secondary circuit is fed to pin 10 of 1€51 by PHC-1 as in the same manners in
charge mode. 1IC5% controls the duty ratio at pin 2 to keep the output of secondary circuit properly.
SECONDARY SECONDARY
RECTIFIER FILTER
CIRCUIT ciRcuIT
Fig. 3
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