Star Tech Journal

S*TJ DECEMBER 1981 4
American
Arcade
Technical
Academy
(Formerly American Arcade School)
* In
depth instructions
on solid state game
equipment.
* Guest
lecturers from
major game factories. Con-
c i se 6 day course, includ-
ing text books aoo technical
manuals.
* Lecture sessions and
in shop training directed
by Don Wright, formerly
Chief Technician at Cine-
matronics.
* Limited space available.
Sessions will be held on
the second and fourth
Mondays of every month
through the following
Saturdays.
4688 Alvarado Canyon Rd.
San Diego, CA 92120
SEGA/GREMLIN
G-80
* POWER * SUPPLY
G-80 POWER SUPPLY
(800-0170)
GENERAL DESCRIPTION
The G-80 Power Supply
incorporates all of the voltages and
audio power amplification neces-
sary to power any G-80 based video
game. One of the major differ-
ences between this and other
Gremlin power supplies is that the
transformer (560-0055) is mounted
separately from the P.C.B./heatsink/
chassis combination. This trans-
former is noticeably larger than
previous units, mainly because it
has isolation windings for driving an
X-Y color monitor as well as
windings for a raster scan color
monitor. Multiple primary taps are
available for using 100, 115 or 230
V AC as the input voltage.
Table 1 lists the ratings of the
regulated DC voltages (a standard
test load) as well as the ratings of
the transformer's windings used to
drive the X-Y or raster scan monitor.
TABLEl
REGULATED DC VOLTAGES
CALL NOW
for information
+SV@6A
-SV@lA
+12V@ lA
-12V@1A
In California
AC (MONITOR) VOLTAGES
(714) 287-4263
Nationwide
1-800-854-2521
Credit Cards Accepted
American
Arcade
Technical
Academy
X-Y: 92 VCT@ 2A
RASTER: 100 or 115 @ 0.65A
VOLTAGE REGULATOR
CIRCUIT DESCRIPTION
The + 5 volt supply consists
mainly of U 1 and the TI Pl 41. U I is
a 723 voltage regulator I.C. which
contains a voltage reference, error
amplifier, series pass darlington
transistor pair and a current limit
transistor. Potentiometer R3 l
( + 5V ADJ) divides the 7.15 (NOM)
reference to 5.0 volts as the input to
pin 5, the non-inverting input of the
723's error amp. Pin 4, the inyerting
input, senses the output voltage. The
internal error amp maintains a voltage
at Ul pin 10 which is higher than the
5.0V output by an amount equal to
the two VBE drops of the TIP141 (a
high current darlington) which acts as
a current amplifier, and the IR
drop across R25. Any change in the
output voltage is sensed at pin 4 which
causes the error amp to drive pin 10
higher or lower in order to keep the
output at a steady 5.0 volts.
A "fold back" current limiter
circuit is composed of R25, R26, R32,
Q7 and the internal current limit
transistor of Ul. This circuit allows
the regulator to operate normally
until the load current increases to the
point where the voltage across R32
reaches the value which starts turning
on the internal current limit
transistor. This transistor reduces the
output current of the regulator to a
fraction of the "knee" current when
the output is shorted to ground.
This feature greatly reduces the
power dissipated in the TIP141 when
the output is accidentally short
circuited. This action occurs so
quickly during a short that fuse F3
should not blow. The value of the
knee current is approximately 6.5
amps, and can be increased or
decreased by decreasing or increasing
R26, respectively.
Capacitors C20 and C21 frequency
compensate the regulator so it won't
oscillate and C 17 filters high
frequencies at the output. Q7 temper-
ature compensates the current limit
circuit. Temperature variations of
its emitter-base voltage closely match
and cancel the base-emitter voltage of
the internal current limit transistor.
Therefore, the knee current of this