20 Circuit Description TB8100 Installation and Operation Manual
© Tait Electronics Limited June 2005
If any of the monitored conditions exceeds its normal range of values, the
microprocessor will generate an alarm and reduce the output power to a
preset level (foldback). If the measured values do not return within the
normal range after foldback, the PA will be shut down.
The alarms and diagnostic functions are accessed through I
2
C bus messages
on the system control bus via the reciter, control panel and Service Kit
software. Some measurements are logged by the microprocessor and this
information can also be accessed through the system control bus.
The operation of the cooling fan mounted on the front panel is determined
by the temperature limits set in the PA software. If two PAs are fitted in a
TB8100 subrack, either PA will turn on the fan when required.
Power Supply The 100W PA operates off a 28VDC external power supply only, while the
5W and 50W PAs can operate off a 28VDC or 12VDC external power
supply, depending on the model. The 12V PAs are fitted with an internal
boost regulator board (refer to “Boost Regulator” below).
The PA also has four internal power supplies which produce –3, +2.5, +5
and +10VDC.
Boost Regulator 5W and 50W 12V PAs are fitted with a boost regulator board. Figure 2.3
on page 21 shows the configuration for a 50W PA, along with the main
inputs and outputs for power, RF and control signals. Note that the 60W
board is only fitted to the 50W PA.
The boost regulator board accepts an input of 12VDC nominal. The input
is firstly fed through the DC input filter, and then through an output filter
and switch which is controlled by a battery control circuit. This output is
fed to the reciter, which operates from 12VDC instead of the standard
28VDC provided when a PMU is used. The output from the DC input
filter is also fed to the power stage where the voltage is boosted to 28VDC,
and is then fed through an output filter to provide the 28VDC output for
the PA circuit boards.
The battery control circuitry monitors the DC input voltage from the
battery. Protection is provided against the wrong input voltage being
supplied. Reverse polarity protection is provided by a diode between
positive and ground, and requires a user-provided fuse or circuit breaker in
series with the DC input line. The fuse or circuit breaker should be rated
at 15A to 18A at 30VDC.
The startup voltage is 12VDC or higher. Once started, the boost regulator
will operate down to 10.25VDC ±0.25V before it shuts down to prevent
deep discharge of the battery.
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