i have a flat panel TV/monitor that's going in a motorhome, it's powered via
a switched mode psu from the mains, which takes 230 volts in, gives 12.33
volts out,

the motorhome uses a 12 volt battery, so most people just connect the tv to
the battery and it all works,

however i've heard of a few people with this type of TV that have had
problems when they are hooked upto shore power, the battery charger being
on-line produces upto 14.8 volts, also if the tv is used when driving for
some reason, the alternator ups the voltage the TV sees to 14.4 volts,

and as the TV is designed to work on exactly 12.33 volts, part of it burns
out when it's fed a higher voltage.. i know this shouldent happen, but it
does, and the TV's makers say the tv was designed for home use not vehicle
use, and it's electronics are optimized for 12.33 volts only, that should be
supplied by the main adaptor, not the 11 to 15 volts automotive electrical
items are designed to handle.

the people who have used this TV in their motorhomes had no problems when
they're not on mains power so the battery charger is off line, the tv works
fine on 12.8 right down to 11 volts, way past when most 12 volt CRT tv's
have turned off, so undervoltage is not a problem really, jsut overvoltage.

So.. i need to build a voltage regulator to power the TV, it pulls 4 amps
max, that's not a problem at first sight,

but voltage regulators need their input voltage to be above the output
voltage, and that's where my problem is,

when the battery is on charge it will have a terminal voltage of 14.8 volts
for a few hours while the charger equalizes the battery bank, then it'll
settle to around 13.8 to 14 volts, still too high for the TV.
when i'm boondocking, the battery will start off at 12.8 volts, and fall as
i use power, i'll stop drawing power when the terminal voltage reaches 11.5
volts usually.

is there a regulator circuit out ther that can handle the 4 amps throughput
i need, and when the voltage is over 12.33 volts on the input side, limit
the output to that voltage, but when the input voltage reaches or goes below
that voltage, it drops out of the circuit? or is able to just pass the
voltage straight through it unregulated.. untill it gets over 12.33 volts
again when i start the engine or plug into a power socket.. where it
regulates the voltage again??