I think that the 2940 regulator needs 11 V minimum, but there are lots
of places for voltage drop ahead of the regulator: The power cable, fuse
and fuse holder, power switch, power connector, and the regulator
socket. Every little bit hurts. I put De-oxit on the regulator chip
leads where they plug into the socket. One of these days, I'll change
the spring-loaded fuse holder and fuse to an automotive blade type fuse.
73,
Bob WB2VUF
Stuart Rohre wrote:
>
> Last night I set down with my Scout schematics and found they do have the
> low drop out LM 2940 in mine, (some 7 plus years old).
>
> Mine does not drift at 12 volts, (and I know of none that do). Down around
> 11 volts, mine drifted once on a bad battery. (Discharged). That battery
> might also have had higher internal impedance due to its age.
>
> Thus, since a number of stages of the Scout operate at regulated 10 volts,
> and the other regulated stages operate from a 7805 type chip (5 volt logic),
> the lower input limit is probably set by the 10 volt bus regulator at 12
> volts DC as indicated in their DC specification in the manual. The 10 volt
> regulator must be looking for a 2 volt difference to maintain regulation.
>
> Thanks Jerry for the cross reference to the chip numbers. Guess there is
> not much to do since they are using 10 volt regulator. ( I think the K2
> uses 8 volts, and thus can operate on internal battery on its discharge
> curve.)
> 73, Stuart K5KVH
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