Hello All,



I have a circuit I'm working on that has 2 busses. The analogue portion
uses 12v, the digital uses 5vd from a 7805 regulator. The regulator
powers a 16f84 pic and 4 7-seg displays.



In the event of a power failure the only portion of the circuit that I
need to maintain power on is the actual pic chip. This means I can drop
power to the 12v rail, the displays are gated on from the pic through
transistors on the common cathode and for current draw concerns during a
power failure I can leave them off somehow. Can anyone point me to any
design notes on a regulator or circuit that will switch my 5volts to a
9v battery to power the 16f84 chip when the incoming 12v power is
missing?





Regards,

Steve

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