Power Supplies; Circuit Board Locations - Data I/O 298 Manual

AC POWER ON/Off
CONNECTOR SWITCH
CONTROL
FAN
PANEL
(KEYBOARD, FIP
DISPLAY,
DRIVER
BOARD
BENEATH)
I
EXPANSION RAM
BOARD
HANDLER
INTERFACE
CONNECTOR
/
SERIAL 1/0
INTERFACE
CONNECTOR
STATUS SWITCH ASSEMBLY
Figure 5-3. Circuit Board Locations
5.3.1 POWER SUPPLIES
Figure 5-4 is a block diagram of the power supply circuitry.
Voltage Selector/Filter
The voltage selector/filter unit provides circuit protection,
filtering and provides the ability to tap different voltages
from the transformer.
Transformer
The power transformer has multiple primary windings to
allow the use of various input line voltages. The secondary
develops appropriate voltages for the rectifiers and filters.
Filter Board
Four rectifier and capacitor filter networks on the filter
board provide the de voltages for the various regulators.
PNP transistors 01 and 02 turn off to isolate
+
40 and
+
HV on high voltage shutdown.
Voltage Regulator
The voltage regulator circuits are located on the controller
printed circuit board.
The
+
5-volt regulator consists of a TL430 shunt regulator
(VR3) driving an MJE 240 (018) which in turn drives two
TIP 35A pass transistors (013 and 014). Feedback is
provided to the TL430 by R42, the voltage adjusting
potentiometer. Foldback current limiting is achieved by
sensing both output current and output voltage. If an
overcurrent exists, 015 senses the increased voltage across
R32 and reduces the base drive to the pass transistor,
which drops the output voltage. When the output voltage
goes below the CR18 Zener diode reference, the base
current flows through CR19 to 015, further dropping the
output voltage. To reset the regulator from its foldback
condition, input power must be removed long enough to
discharge C37. If an over-voltage condition exists, CR20
will begin to conduct, causing 016 to pull base current
from 018.
The 24-volt supply and the 48-volt supply work on the
same principle as the 5-volt supply. The difference is that a
current source, rather than an emitter follower, is used to
supply base current to the pass transistors.
5-3
10-990-0013