206 Power Management Unit Circuit Description TB8100 Service Manual© Tait Electronics Limited September 200612.2 AC ModuleThe AC module accepts an input of 115/230VAC 50/60Hz nominal, andprovides two regulated 28VDC outputs: high current for the PA, and lowcurrent for the reciter.The main circuit blocks are shown in Figure 12.3 below, and are describedin more detail in the paragraphs which follow.EMC Filter,Protection, and ACSwitchThe AC input is fed first to an EMC filter consisting of two common-modeand two differential-mode filters. The input voltage is monitored, and if itis within the specified voltage range, a “mains OK” signal is sent to themicroprocessor via an opto-coupler. If the mains input voltage is outside thespecified range, the power factor stage is inhibited to protect the ACconverter from damage.An MOV is fitted between line and phase to clamp low energy noise on theline. A 10A fuse is also fitted for additional safety. If the fuse blows, itdisconnects the PMU from the mains. Inrush current control is provided bya high power resistor, which is bypassed by a relay when the PMU ispowered up.Power FactorCorrection (PFC) The filtered AC input is fed to this boost power supply where the activepower factor correction circuit converts it to the regulated 400VDC output.This stage is fully protected from overload and short circuit by the powersupply control circuitry.Figure 12.3 PMU AC module block diagramEMC Filter,Protection,& AC SwitchPower FactorCorrection(PFC)High Voltageto DC(HVDC)SystemInterfaceandFan ControlPFC Control HVDC Control AuxiliaryPower Supply*Current SenseandOutput FilterInterface toDC Module MicroprocessorAC I/P115/230V50/60HzDC*optional (mounted on DC module)Control &Monitor28VDC O/P(PA)DC O/P13.65/27.3/54.6V28VDC O/P(Reciter)SystemControl BusFan
