— 9 —
6. CIRCUIT EXPLANATION
6-1. Power supply circuit
Q1 : Transistor for controlling voltage (VP)
Q2 : Transistor for voltage detection
Q3 : Transistor for controlling power down (PWD) signal
ZD2 : Zenner diode for controlling base current of Q2
ZD3 : Zenner diode for detecting power down (PWD) signal
After plugging the AC cord into the outlet, the AC voltage (23.8 V) appears at CN1 connector.
Then this voltage is rectified by the diode bridge and it become constant voltage through the capacitor
C1.
[Voltage VP]
A constant voltage (31.4 V) appears on the "2" position. This voltage made from the constant
voltage circuit consist of transistor Q1 and Q2, zener diode ZD2, resistor R7, R8, R12 and R13.
[Voltage VLED and VCC]
The voltage goes to pin No.1 of regulator IC1 and then it is out from pin No.2 of IC1 as stable
voltage (5.6 V).
Then this voltage falls down to 5 volts through the diode.
It is used for VCC (for logic) and VLED (for display drive).
Also, it goes to pin No.4 of IC1 and using to control the output voltage level.
Inductor L1 is used to stabilize the VCC voltage when the drawer opened.
FROM TRANSFORMER
F1
D2
1SR35-100A
1SR35-100A
1SR35-100A
1SR35-100A
D1
D4
D3
C4
50F2S683J
CN1
5277-02A
1
2
C1 3300µF50WV
Q2
R121K
2SC4640
C5
C103
ZD2
RD7·5EB3
R13
2.7K
R8
R7
C9
5.1K
820
ZD3
R15 10K
RD16EB3
Q3
2SC4640
1µF50WV
C6
50RE2-47
R14
100K
D9
1S2473
Q1
2SD1196
WITH HEATSINK
OSH-1625-SP
IC1
VIN 1
VIN
GND
VOUT
LM2575T-5.0
3
4
2
5 ON/OFF
OUTPUT
FEEDBACK
47~63KHz
MCDR1419-681K
L1
D8
RK-14
25RE2-330
C8
1S2473
D7
D11
1S2473
PWD
VP 24V
VLED 5.6V
VCC 5.0V
GNDP
GND
GND
1
2 5 7 8 9
3
4
6
10
11
12
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