122 Power Amplifier Circuit Description TB8100 Service Manual© Tait Electronics Limited September 20067.3 Boost Regulator Circuitry (12V PA Only)5W and 50W 12V PAs are fitted with a boost regulator board. Figure 7.1on page 114 shows the configuration for a 50W PA, along with the maininputs and outputs for power, RF and control signals. Note that the 60Wboard is only fitted to the 50W PA.The boost regulator board accepts an input of 12VDC nominal. The inputis firstly fed through the DC input filter, and then through an output filterand switch which is controlled by a battery control circuit. This output isfed to the reciter, which operates from 12VDC instead of the standard28VDC provided when a PMU is used. The output from the DC inputfilter 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 forthe PA circuit boards.The battery control circuitry monitors the DC input voltage from thebattery. Protection is provided against the wrong input voltage beingsupplied. Reverse polarity protection is provided by a diode betweenpositive and ground, and requires a user-provided fuse or circuit breaker inseries with the DC input line. The fuse or circuit breaker should be ratedat 15A to 18A at 30VDC.The startup voltage is 12VDC or higher. Once started, the boost regulatorwill operate down to 10.5VDC ±0.25V before it shuts down to preventdeep discharge of the battery.Note These limits are set in hardware at the factory and cannot beadjusted by the user.Power SavingOperation Power Saving is also available in base stations using a 12V PA. Both Sleepand Deep Sleep modes can be configured, with the same receiver cyclingand Tx keyup options as a base station with a PMU. In Deep Sleep mode,the reciter shuts down the PA by shutting down the boost regulator boardin the PA (via an external control cable 1, as shown in Figure 19.4 onpage 292). The 12VDC output from the boost regulator board isunswitched and continues to power the reciter even when the rest of thecircuitry on the board is shut down.1. Refer to the TB8100 Installation and Operation Manual (MBA-00005-xx)for more information on this connection.
