Sharp ER-A57R1 Service Manual page 70

4. Power supply circuit
The ER-A550 supplies +5V to +24V, and ±12V is generated from
+24V in the DC/DC convertor circuit.
ZD1
RD27EB4
+24V
T800mA
+ C49
100µ Q1
50V
+5V
D1
1
E352 3
IC9
2
R22
c
4.3K
C50
ZD3
10µ
RD5.1EL1
C
16V
PX
(1) The PX signal from the OPC1 alternately turns on and off the
comparator output of IC 8 (pin 7), which causes Q1 to turn on
Α
and off. (Circuit )
3.255µs
PX
Point c
Q1
OFF ON
ON,OFF
T1: Software starting:
Normal operation:
∗ After POFF cancel (Power ON), software start is made for
13.3ms.
Duty (Q1: ON/OFF) : Software strating: 12.5%
Noemalperation : 25%
(2) The potential at point
+12V(About +11V). A load fluctuation causes the +12V output to
β
change. At point of the comparators (+) side, a triangular
waveform appears as shown in Fig. 4-2.
(3) The comparator (IC No. 8...Circuit
is compared with that of point
β
lower than point , Q1 activating time is prolonged to raise
the output voltage (by increasing the duty cycle). On the con-
trary, if the potential at point
ing time is hortened to decrease the output voltage (by decreas-
ing the duty cycle). As Q1 duties cycles are varied by detecting
the +12V output fluctuation in the comparator (Circuit
output voltage is regulated at a constant level.
PX
Point b
Point a
Point c
Q1
ON, OFF OFF ON OFF
Point a
+3V
*1
Point c
100µ35V x 2
T1
H6752RC RD 33E B1
+12V
+
D 2
C51
ZD2
R17
+ 2.7KG
C52
D 3
-12V
R18
+5V
+24V
2.2KG
R24
2
8 a b
2.2K
-
1
3
+
IC8
4
C28
9393
R14
330P
10KG
R16 R15
10K 10K
6
+
7
5
-
IC8
9393
Fig. 4-1
T1
OFF ON OFF
Fig. 4-2
26.04us
13.02us
α
is 4.8V when the output voltage is
Β
), the potential at point
β
. If the potential at point
α
is higher, the transistor activat-
ON OFF ON
(a)
*2
Fig. 4-3
Potential at point a changes according to a fluctuation in the
+12V output. Waveform at point a differs depending on the state
of +12V output.
(4) The pin 3 output of the IC9 chip at circuit
when the pin 1 input is at 5V. But, when it drops below 4.5V, the
line goes to the GND level. This causes Q1 to turn off so that
+12V and 12V are shut off. It is provided for prevention from
malfunction in the logic circuit when the +5V supply from mal-
function in the logic circuit when the +5V supply from the ER-
A550 main frame drops.
∗ IC9: Not used
R13
B
100K G
5. ER-A5RS channel setting
A
The ER-A5RS ports can be set to channel 1 - 7 and invalid (inhibit)
with SW1 on the PWB.
OPTCN1
+5V
GND
SW1 setting contents
+5V
SW1 1~3 are used for channel setting of RS-232 connector 1
GND
(RSCN1).
SW1 4~6 are used for channel setting of RS-232 connector 2
(RSCN2).
SW1
3 2
0 0
0 0
0 1
0 1
1 0
1 0
1 1
α
1 1
α
is
Note
1) If RSCN1 port and RSCN2 port of the ER-A5RS are set to the
same channel, RSCN2 port becomes invalid and only RSCN1 is
valid.
2) If RSCN of the ER-A5IN and the ER-A5RS connector are set to
Β
the same channel, the buses compete and the operation cannot
), the
be assured. In addition, it may break the hardware. Never set the
two to the same channel. Be sure to set them to different channels
+5V
or to set invalid.
GND
+5V
500mV
+4.8V
+1.4V
GND
OFF
+4.8V
*3
+1.4V
GND
4 ™ 27
(1)
(0)
RSCN1
setting
1
0 RS-232 invalid
1 Channel 1
0 Channel 2
1 Channel 3
0 Channel 4
1 Channel 5
0 Channel 6
1 Channel 7
CN2
6 5 4
1
0
Χ
is at a high level
SW1
RSCN1
RSCN2
SW1
RSCN2
setting
6 5 4
0 0 0 RS-232 invalid
0 0 1 Channel 1
0 1 0 Channel 2
0 1 1 Channel 3
1 0 0 Channel 4
1 0 1 Channel 5
1 1 0 Channel 6
1 1 1 Channel 7
CN1
3 2 1