Casio 200cR, Service Manual, Page: 12 / 68

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5. Circuit explanation
5-1. Power supply circuit
Q1 : Transistor for controlling voltage (VP)
Q1 : Transistor for voltage detection
Q3 : Transistor for controlling power down (PWD) signal
ZD2 : Zenner diode for controlling base current of Q2
ZD1 : Zenner diode for detecting power down (PWD) signal
After plug the AC cord into the outlet, the 24 volts of AC voltage appears between T1 and T2.
Then this voltage is rectified by the diode bridge and it become constant voltage through the
capacitor C1.
[Voltage VP]
A constant voltage (17.9V) appears on the C point. This voltage made from the constant voltage
circuit consist of transistor Q1 and Q2, zenner diode ZD2, resistor R2, R3, R4 and R5.
[Voltage VLED and VCC]
The voltage goes to 1 pin of regurator IC1 from B point and out from 2 pin of IC1 as stable voltage
5.5 volts. Then this voltage down to 5 volts through the diode.
It is used for VCC (for logic) and VLED (for display drive).
Also, it goes to 4 pin of IC1 and using to control the output voltage of 2 pin.
Capacitor C5 is used to reduce the ripple of this voltage.
Inductor L1 is used to stabilize the VCC voltage when the drawer opend.
2
1
5277-02A
CN1
TRANS
F1
PWD
C1
50F2S683J
C2
ZD2
ZD1
RD13EB3
R5
R1
560
2.2K
RD5.6EB3
R3
3.9K
35V3300
R4
R50X-2K
1SR35-100A
D2
D5
1SR35-100A
1SR35-100A
D4
1SR35-100A
D3 C6
25V33
C5
D1
1S2473
D6
1S2473
D7
RK-14
25V330
C3
GND
35V47
Q1
WITH HEAT-SINK
D1276A
R2
1.2K
Q2
C945
R7 Q3
R9
10K
VDD
LM2575T-5.0
VIN1
VIN VOUT
L331K L1
IC1
3
GND
5
2
4 ON/OFF
OUTPUT
FEED BACK
C945
D8
1S2473
4.7K
GND
D10 1S2473
VP
VLED
VCC
J
K
A
B
D
I
C
H
F
G
E