Appendix B. Power Distribution; Battery Backup - Ricoh FAX220 Service Manual

APPENDIX B. POWER DISTRIBUTION

1. PSU/FDU
The PSU regulates the 120
or 220 to 240 Vac input to
generate +24 Vdc. The
+24Vdc is then supplied to
the secondary power sup-
ply circuit on the FDU to
generate ± 5 Vdc. The
+24VSW for the thermal
head is switched on by the
FCE when a fax call is com-
ing in; this voltage is
watched by the FCE to
check for overload.
2. Battery Back-up
On the FCE board, the sys-
tem memory SRAM and
the KFCP, which controls
the real time clock's oscilla-
tor, always have to be
backed up by dc voltage.
When the power is sup-
plied from the PSU,
VCC (+5V) and +5VBAT
back up these ICs. When
power is not supplied from
the PSU, the voltage detec-
tor on the FCE connects
the BAT signal, upon which
+3Vdc is supplied from the
battery on the FDU, to
+5VBAT, so that it can
back-up these ICs.
3. LIU Back-up
When the power is not supplied from the PSU, the internal telephone unit is still active. When the handset is picked
up or the On Hook Dial key is pressed, the dc loop in the LIU circuit is closed. Then the speech and ring detection
circuit regulates the line voltage to wake up the microcontroller on the LIU. For more details, see Appendix A "Line
Interface".
OPU
+5V
-5V
120/220-240 Vac
FDU
PSU
+24V
+24V
Cutter
120 /220-240 Vac
PSU
+24V
Sensors
SBU
+5V +24V
+5V
+24V Switch
+24V Overload Check
DC-DC
+5V Regulation
Switcher
IC1
(MC34063AP1)
-5V Regulation
+5V +24V
LED Array
Tx/Rx Motors
FDU
DC-DC
Switcher
IC1
(MC34063AP1)
BAT2
(3V)
FCE
+5VBAT
KFCP
SRAM
IC1
IC7
(MH62256)
(RF5A47)
System Memory
B-1
+5V and/or -5V
+24V or +24VSW
+5V
+24V
+24V
+24VSW
CK24V
POWON
+5V
(VCC)
+5V
-5V
-5V
+24VSW
+24V
+5V
T/H
+5V Regulation +5V
(VCC)
BAT VCC
BAT VCC
Voltage Detector
IC2
(BH9751F)
VCC
XTL 1
32768Hz
For Real Time Clock
LIU
FCE