Owner`s manual

4.8.1.7 High Voltage Drivers
The processor PCB also has a high voltage transistor array (ULN7002), which is used to control the tri-colored
“STATUS” LEDs and “alarm relays”. The LEDs are powered directly from the 48V input bus through dropping
resistors. The transistor array shorts out the appropriate Red and/or Green LED to produce the Green, Amber, or
Red color. The “Alarm” relays operate directly from the +48VDC supply, thus the high voltage driver is needed.
4.8.1.8 Under Voltage Detector
The “Controller” circuit board also has an under voltage detector (U4) which inspects the +14.97V regulator voltage.
The “reset” line will be held low until supply voltage is greater than +12.275V. A “reset” signal is issued if the voltage
falls below this level.
4.8.1.9 Sine Wave Reference
Sine wave reference signal is obtained from the 80C196KC processor, which has three PWM outputs. One of these
is used to generate the phase locked sine wave reference voltage. The amplitude is set at the time of calibration
and the calibration constants are stored in the EEROM. Default values are in PSD301 ROM. The output of this
PWM signal is buffered (U7) and applied to an optical coupler (U12). The coupler provides isolation between the
primary (battery) side circuitry and the secondary (AC output) circuitry. The optical couplers output amplitude is
stabilized by a +5V regulator (U13) and FET switches (Q5, Q6) and then filtered by a two stage R-C filter (R60, R61,
C40, R62, C41) than level shifted and phase corrected by C42 and R63. The buffered (U14) reference sine wave
is now applied to the system “Voltage Error Amplifier”, U14 through ad DC blocking capacitor. Feedback to the error
amplifier is from the output of the 120VAC inverter, connections being made at the input terminals of the EMI filter.
An optically coupled FET switch is placed in series with the output of the Voltage Error Amplifier so as to be able to
disconnect it from the system in the advent of a failure in the processor. Isolation resistors are provided in the
“Voltage Error Amplifiers” output that goes to each power module. This will prevent a system failure if one of the
control lines should become shorted to ground.
4.8.1.10 “Display” Driver
Output to the LCD display is isolated by means of diodes. The LCD is powered from the 48V input supply and
regulated via a 5.1V zener and diode so as to produce +5.7V for operating the LCD module. This compensates for
the isolation diodes in the output of the LCD signal lines. LCD actually operates at +5.0VDC.
4.8.1.11 “Controller” Selection
The cross-coupled optical coupler (U17) and FET (Q10) generate the MASTER control signal (I/O port P1.4). A “1”
to the processor tells it that it is in control. A green LED located on the processor PCB will be illuminated if the
processor is operation. The LED can not be seen when the LCD panel is in place.
4.8.2 Static Switch
The “ Static Switch” consists of a parallel connection of a dual Silicon Controlled Rectifier (SCR) module, anode of
SCR1 connected to the cathode of SCR2, anode of SCR2 connected to the cathode of CR1. This module is mounted
on a heat sink, 12” long, 5.15” high, 1.5” thick. The heat sink is cooled by two AC powered fans. The purpose of the
dual fan is for redundancy. If one of the fans should fail, the other fan can cool the SCR module until the unit can be
serviced. The “Utility” AC input, if available, will be connected to a terminal block TB1-2. The system output is on
TB1-1. TB1-2 and TB1-4 are AC returns. TB1-2 is connected to the dual SCR module. The other side of the SCR
module connects to TB1-1 and also to the “EMI” filter, which in turns connects back to inverter output. Several
different SCR modules used in the system. The current rating of the modules changes with respect to the number
of power module positions available in the “receiver” rack. The one and two module system will utilize an IXYS
“MCC72-16io1 B”, the three and four module system will utilize an IXYS “MCC132-16io-1”, the five and six module
system will use an IXYS “MCC220-16io”. A 480V “Metal Oxide Varistor” (MOV) is connected across the SCR module.
Owner’s Manual
Theory of Operation page 4 — 13