SECTION M
DC REGULATOR (A30)
M.1
Introduction
This section describes the DC Regulator, and includes trou-
bleshooting information. The UC3834 integrated circuit voltage
regulators used on the DC Regulator are also used on other
boards in the transmitter; this section describes all positive and
negative voltage regulator circuits using this integrated circuit.
The DC Regulator supplies B+ (+5.75 VDC regulated) and
Modulated B- voltage for Modulation Encoder/Binary A37. Un-
reg22 VDC for cable interlock sensing on the Modula-
tion Encoder also passes through the DC Regulator. Fault sensing
and metering circuits for these supplies are located on the DC
Regulator. The DC Regulator is located in the Left Control
Compartment.
M.2
Principles Of Operation
Refer to Schematic 839-7855-163 in the Drawing Package.
M.2.1
Circuit Grounds on the DC Regulator
Grounds for the B+ (+5.75 VDC) and Modulated B- supplies are
kept separate on the board. On the DC Regulator Schematic
Diagram, the grounds are referenced as “A” and “B”, along with
a power supply ground. The grounds are brought separately to
the cabinet ground at the low voltage power supply to minimize
ground loops and AC and RF noise.
M.2.2
UC3834 Integrated Circuit Linear Regulator
On the DC Regulator, four UC3834 regulators are used, one in
each of the B+ (+5.75 VDC) supplies and the other two in the
“Modulated B-” supplies.
M.2.2.1
Other Supplies Using the UC3834
This IC is also used in on-board regulated supplies on other
printed circuit boards in the transmitter. Additional regulated
supplies using this IC are:
a. Analog to Digital Converter (A34)
1. -15 Volt supply
2. +15 Volt supply
3. +5 Volt supply
b. Analog Input Board (A35)
1. -15 Volt supply
2. +15 Volt supply
c. Output Monitor (A27)
1. -5 Volt supply
2. +5 Volt supply
d. Controller (A38)/LED Board (A32)
1. +5 Volt supply
2. +15 Volt supply
3. -15 Volt supply
M.2.2.2
Linear Regulator IC Description
The UC3834 integrated circuit voltage regulator can be used for
either positive or negative regulated supplies. Figure M-1 is a
block diagram. An external pass transistor is used to increase
current capability. The integrated circuit has internal reference
voltages, internal fault monitoring, and a “Fault Alert” open-col-
lector output for external logic and indicator circuits. An external
compensation network at pin 14 is required to ensure regulator
stability. The current sensing feature is not used in any supply in
the transmitter, and the Current Sense input terminals (IC pins 6
and 7) are simply shorted together.
M.2.2.3
Regulator
Circuit Operation
The basic regulator is
conventional, and con-
sists of the internal
vo l t ag e
ref ere nc e
which is compared
with a sample of the
supply output voltage
by the error amplifier.
Figure M-2 (a) shows a
basic positive regula-
tor, and Figure M-2 (b)
shows a basic negative
regulator. The error
amplifier output is the
input to a driver ampli-
fier in the IC, with in-
ternal over-current
p r o t e c t i o n f o r t h e
driver amplifier. The
Figure M-1. Block Diagram, UC3834 Linear Regulator
888-2297-002
M-1
WARNING: Disconnect primary power prior to servicing.
