TB8100 Service Manual Reciter Circuit Description 59© Tait Electronics Limited September 20062.7 Power SupplyRefer to Figure 2.13 on page 60.The reciter is designed to operate from the +28V regulated supply providedby the PMU. The nominal +28V supply enters the reciter digital board andpasses through an overcurrent and overvoltage protection section beforebeing distributed. The protected +28V output supplies the controlcomparators, fan switch, and main regulators. There is one regulator on thedigital board and another on the RF board.RF Board The main regulator is a switched mode converter that has two outputs: theflyback portion generates +8.5V, and the buck portion generates +5.3V.The +8.5V supply is regulated to +8.0V for reticulation to the RF circuits,either directly, or via switching circuits used in power saving modes. The+8.5V supply is also used to power the analogue sections of the systeminterface board (via the digital board).The +5.3V supply is regulated to +3.3V to power the RF synthesizers.The RF board has a charge pump converter that generates +23V from boththe +5.3V and +8.5V supplies. This is used to supply the active loop filtersof the RF synthesizers. The +8.5V output and the +5.3V supply to thecharge pump can be switched as part of the power saving modes.Digital Board The main regulator is a switched mode converter that has two outputs: theflyback portion generates +5.3V, and the buck portion generates +3.3V.The +5.3V output supplies the op amps associated with the CODECs andis distributed with regulators: +5V for the ADC, +5V for the system, and+3V for the 40MHz clock circuitry. The +5.3V and +5V regulatedsupplies can be switched as part of the power saving modes.The +3.3V output is distributed to the remaining circuitry and to the+2.5V regulator for the DSP. These are switched as part of the power savingmodes. The +3.3V output is also supplied to the system interface board viaa protection circuit.
