Hello.  I've been thinking about a way to build voltage regulator that runs on a battery, let's say 3.3V or something.  With a fresh battery, this voltage regulator is on and regulates down to, say 0.8V, but as the battery voltage drops down to 0.8V, the regulator senses this low battery voltage and bypasses itself, so that the battery is connected directly to the regulator output. Basically, this regulator shuts itself off when regulation is not needed when it senses low supply voltage.

I appreciate any idea you may have.

Regards,
ccd

Thanks for your response, but what I'm looking for is NOT  how to design a LDO regulator, but a way to sense low supply voltage and bypass the regulator because the regulator is no longer functional  at this low supply voltage.  What I could do is use a low voltage bandgap reference (0.6V perhaps) to detect the voltage drop to pull the gate of the pmos regulator driver low to short the load to the supply at that point.

Thanks Raul.  

I'm concerned about LDO not naturally going into dropout when the error amp and bandgap reference are also on the same battery as the LDO.  When the battery voltage drops, the error amp becomes non-functional or partially functional, will it still correctly drive the gate of the LDO pmos device low?  This is why I think a comparator and another voltage reference are needed to ensure the LDO is disabled.

I hope my thinking is wrong and that the comparator and voltage reference are not needed. Please give me your feedback.

Thanks again,
ccd