P.9
Power Supplies
On-board regulators 5 Vdc for all logic circuits on the
Controller, and +15 Vdc and -15 Vdc for the analog meter
drivers. A “+5B” back-up supply, which supplies all critical
memory circuits when the transmitter’s primary power fails or
is turned off, is also located on the Controller.
These supplies also provide operating and backup voltages for
LED Board. Sheet 5 of the Controller schematic diagram shows
the voltage regulator circuits and “Supply Fault” logic circuits.
P.9.1
Voltage Regulator Integrated Circuits
Refer to SECTION M, DC Regulator, for descriptions of the
voltage regulator circuits using UC3834 linear voltage regulator
IC’s.
P.9.2
+5B (Backup) Supply
The +5B supply includes BT1, BT2 and BT3 (optional back-up
batteries), a one farad energy storage capacitor C44, diodes CR6
and CR7, and current limiting resistors R17 and R18. This
circuit is shown on sheet 5 of the Controller schematic diagram.
P.9.2.1
Energy Storage Capacitor
The back-up supply uses a one farad low-voltage storage ca-
pacitor C44. The capacitor is charged from the +5 Vdc supply,
through diode CR6 and resistor R17.
If the +5 Vdc supply is not active, either because of AC power
loss or a supply fault, diode CR6 is reverse-biased. Capacitor
C44 discharges only into the circuits on the Controller and LED
Board. Total current drain on the back-up supply is less than 1
milliampere, so that the capacitor alone can maintain memory
for two hours or more.
NOTE
All Integrated Circuits supplied by the +5B backup supply are
low-power devices. Do not replace these IC’s with devices from
other logic families.
P.9.2.2
Back-up Supply Capacitor Charge Time
If the transmitter has been off for a long period of time and the
back-up supply capacitor is discharged, it will take approxi-
mately one minute for the capacitor to charge.
NOTE
If back-up supply capacitor C44 has discharged, the transmitter
control circuits will not respond for approximately one minute
after first applying transmitter power. It will then be necessary
to set HIGH, MEDIUM, and LOW power levels again.
P.9.3
Battery Back-up
If memory back-up for extended periods is required, AA batter-
ies should be installed. Diode CR7 prevents reverse current flow
into the batteries. DO NOT USE RECHARGEABLE BATTER-
IES, SUCH AS NiCad BATTERIES. This circuit is not designed
to recharge batteries. Ordinary carbon batteries can be used, but
alkaline batteries are recommended, as they are less likely to
leak and their longer “shelf life” will be an advantage in this
low-current application.
NOTE
Do not install back-up batteries unless C44 is charged (+5B
voltage at TP6 is greater than 4.5 Volts). Current drain from the
batteries into C44 will shorten battery life.
P.9.3.1
Replacing Batteries
Because of the very low current drain, the life of back-up
batteries BT1, BT2, and BT3 should approach the battery shelf
life. It is recommended that batteries be replaced yearly.
P.10
Supply Fault Circuits
Figure P-8 is a simplified diagram of the Supply Fault circuit
on the Controller. If output voltage of any of the three voltage
regulators is more than 10% low or 10% high, the regulator
generates a “Fault Alert.” A “Fault Alert” from any one of the
three regulators on the Controller generates the following out-
puts:
a. Regulator Fault Summary: Illuminates LED DS1
b. “Data Clear-L” logic signal to Analog Input Board.
c. “Supply Fault-L” logic signal to power control logic,
turn-on/turn-off control logic, and the LED Board.
“Supply Fault-L” and “Data Clear-L” logic signals are gener-
ated as soon as a “Fault Alert” output occurs, but are held LOW
for approximately .25 seconds after the last Fault Alert on the
board clears. This “off” delay is part of the AC Recycle function.
When AC power returns after a power failure, the AC Recycle
automatically turns the transmitter back ON at the same power
level and output as before the power failure. This will occur if
no other faults are detected and if the power has not been off
long enough for the +5B back-up supply to discharged. The +5B
supply retains power level and output power data memory for
at approximately two hours with no batteries installed.
P.10.1
Regulator “Fault Alerts”
The fault alerts connect to a common line, which is logic HIGH
when no supply faults exist and logic LOW if one or more
regulators have active “Fault Alert” outputs. This supply fault
line goes to a “Regulator Fault Summary” indicator and to a
“Fast on-slow off” delay circuit.
If all “Fault Alert” outputs are “HIGH” the inputs to inverters
U49-2 and U50-2 are pulled to +5 Vdc by R36. If a +5 Vdc or
+15 Vdc supply “Fault Alert” is present, the inputs to U49-2 and
U50-2 will be logic LOW. If the -15 Volt supply “Fault Alert”
is present, R35 and R109 form a voltage divider and Schottky
diode CR11 conducts to clamp the inputs to U49-1 and U50-1
at a few tenths of a Volt negative.
P.10.2
“Regulator Fault Summary” Indicator, DS1
When there are no Fault Alerts, inverter U50-2 is LOW and DS1
is off. When a “Fault” occurs in one or more regulators, U50-2
goes HIGH and illuminates DS1.
P.10.3
“Fast On-Slow Off” Delay Circuit (U49-4)
This delay performs an “AC Power recycle” function. When AC
power returns after a power failure, the “slow off” holds the
DX-25U
P-18
888-2297-002
Rev. S: 05-02-97
WARNING: Disconnect primary power prior to servicing.
