User Manual

TR-800 Service Manual
-14-
Power Management
Theory of Operation
Battery Revert Circuit:
A voltage reference network consisting of CR0212, CR0213, R0268, and VR0209 provides a stable
voltage reference of 7.5Vdc. This reference voltage, at the anode of VR0209, is applied to the negative
input of the Over Voltage Detector U0206B-6, to the positive input of AC Fail Detector U0206A-3, and to
the positive input of the Low Battery Detector U0205B-5. Operating positive supply voltage for the
integrated circuits is obtained from the TR-800 power supply through CR0212 when the TR-800 is
operating on AC mains input power. The supply voltage is obtained through CR02013 when the station is
operating on the battery.
During normal operation under AC mains power, the negative input of the AC Fail Detector U0206A-2 is
more positive than the positive input U0206A-3. The output of U0206A-1 is low and Q0224, the driver for
relay KR01, and Q0216, the “BATTERY ON” driver, are turned off. When AC mains power is lost, the
voltage at U0206A-2 becomes lower than the reference voltage applied to U0206A-3. The output at
U0206A-1 then goes high and turns on both Q0224, which activates relay KR01 and transistor Q0216,
which provides a low at the output point “BATTERY ON”. The “BAT ON” LED, CR0219, illuminates to
indicate the DC power supply is operating.
If the battery voltage falls below approximately 10.2Vdc, the output at U0205B-7 will go high. This action
turns on Q0218 that shunts the base drive to Q0224 through CR0217 and turns off the relay. Q0218 also
provides a low through CR0218 at output point “BAT LOW”. This auxiliary output might be used to key a
portable radio to signal the repeater operator that the battery has exceeded the low voltage limit for the
radios. Hysteresis is provided by the feedback network consisting of CR0221, R0289 and R0288 from
the output of U0205B-7 to the positive input U0205B-5. The reference voltage at the positive input of
U0205B-5 is increased such that the battery voltage must rise above 12Vdc before relay KR01 will
reactivate and place the TR-800 back on battery power. This latching action is used to prevent
excessively deep discharging of the battery.
The repeater will remain turned off until either AC mains return or a charged battery is substituted for the
discharged battery. The circuit consisting of C0233, R0285, R0286, CR0220, R0287 and Q0217 resets
U0205B-7 to low upon the return of the AC mains power.
Capacitor C0234 at the negative input of U0205B-6 smoothes the variation in the battery voltage
between the transmit radio keyed and unkeyed conditions. Capacitor C0230 at U0206A-2 input, in
conjunction with C0234 at U0205B-6, ensures proper resetting of U0205B with the return of the AC
mains power.
The Over Voltage Detector consisting of U0206B and resistors R0274, R0275 and R0271 monitors the
DC output of the TR-800 power supply. If the voltage exceeds 16.4Vdc, the output of U0206B-7 goes
high and turns on relay driver Q0224. The station switches to battery power although there is no
indication at the “BAT ON” output point.
Zener diodes VR0210, VR0211, VR0212, VR0215 and VR0216 protect the electronics from damage by
accidental static discharge.
Fuse F0203-15A and diode and CR0215 provide protection from reverse polarity if the battery is
inadvertently connected “backward”.