每个背板流行multisupply巴士（如VME，VXI和PCI）提供电源有限的输出3.3V，5V，±12V（±24V）。如果这些系统线卡增加3.3V或5V电源的要求，功率预算，从而可以支配的电路利用其从负载较轻的-12V源的功率。
Maxim>AppNotes>AUTOMOTIVEPOWER-SUPPLYCIRCUITSKeywords:3.3VSupplyTapsPowerfromthe-12VPCIBusFeb07,2000APPLICATIONNOTE2963.3VSupplyTapsPowerfromthe-12VPCIBusAdditionalInformation:qQuickViewDataSheetfortheMAX668qSamplesandLiteratureOrderFormqTechnicalSupport:PowerThebackplanesofpopularmultisupplybuses(suchasVME,VXI,andPCI)eachprovidepower-limitedoutputsof3.3V,5V,and±12V(or±24V).Ifaddinglinecardstothesesystemsincreasestherequirementsfor3.3Vor5Vpower,thepowerbudgetthuscandictatethatacircuittapitspowerfromthelightlyloaded-12Vsource.Thefigurebelowshowsacircuitthatderives3.3Vfrom-12Vbyboostingthe-12Vs
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