User Manual

TR-800 Service Manual
-15-
Variable speed, Temperature controlled Fan Circuit:
The TL431AILP is a three-terminal programmable shunt regulator diode. This monolithic IC voltage
reference operates as a low temperature coefficient zener that is programmed from 6Vdc to 12Vdc with
a resistor network consisting of R0296, R0297 and an NTC thermistor Rth0201. Q0219 operates as a
fast power switch between “ON” and “OFF” (similar to PWM mode) controlled by the output at cathode of
TL431AILP. The rotating speed of brushless fan is voltage controlled at collector of Q0219. The higher
temperature, the higher power supply to the fan, hence the faster it rotates.
Battery charging (Float Maintenance) Circuit:
The battery charging circuit is intended for use with sealed lead acid gel cell batteries. The charging
current, limited to approximately 400mA, is used to maintain a “float” charging condition on the battery.
After operating the TR-800 station on the battery for long periods of time, or if the battery reaches the low
battery limit of the revert circuit, the battery must be recharged with an external high-current charger.
Recharging with the internal trickle charger requires an extended period of time.
The trickle charging voltage is derived from AC mains. Resistors R0269 limit the charging current to
approximately 400mA to a partially discharged battery (terminal voltage of 12Vdc). Once the battery is
fully charged, the current will decrease to 10 to 25mA to float the battery at a terminal voltage of 13.6Vdc.
NOTE
This trickle charger is intended to maintain the
battery for long periods of time between power
failures and is not intended for charging a fully
discharged battery. If the battery is completely
discharged, it must be removed and charged via a
battery charger with higher current capability.
Figure Block DiagramⅡ