Fig. 3-7 Voltage Regulator - Canon NP-70 Service Manual

3-40
NP~ 70
2) VOLTAGE REGULATOR— NP -70
Fig. 3-7 depicts one of the voltage regulators used in the NP-70. Its operation is as follows:
a) In this regulator, R2 and ZD 1 form the
constant-voltage circuit &transistor Q3
operates as the Difference Amplifier.
Fig. 3-7 Voltage Regulator
b) Initially, the output voltage is felt across the divider circuit R3, VR1 & R4 and a po-
tential is applied to the base of Q3. Also, constant voltage Ez is applied to the emitter
of Q3.
c) If the output voltage (Eo) decreases for some reason, the voltage applied to the base of
transistor Q3 will also decrease. Since the voltage applied to the emitter of Q3 is held
constant, the decrease of the voltage at the base causes the transistor to conduct less.
d) With the reduced conduction of Q3, the voltage dropped across resistor R1 decreases and
the potential applied to the base of Q2 increases. Conversely, the current flow through
Q2 & Q1 increases and output voltage Eo increases to its original level.
e) If the output voltage increases, the previous operation is reversed resulting in a reduction
back to the correct output voltage level. The output voltage can be varied as desired by
using potentiometer VR 1.
NOTE: Due to large current flow, two transistors have been used to reflect a high
impedance to the difference amplifier.
3.4-4 "RAPID-START" ILLUMINATION CIRCUIT (ALL COPIERS)
Original exposure lamps FL2 & FL3 are illuminated at the start of each copying cycle and
must produce a stable light output. Therefore, it is necessary to preheat the filaments prior
to each machine cycle. This is accomplished by applying a continuous voltage to the fila-
ments of the fluorescent between copying cycles. Additional warm-up
"boost" is provided
by the electromagnetic field radiator, which also operates between cycles. This process is
called the "Rapid-Start" method.
Second
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