AVR-Chat

>>> techyf@yahoo.com 26/11/2004 3:01:34 pm >>>
As I am new to electronics, it would be of great help to me if you
could let me know some of the low drop-out version of the 7805 ? For
eg., brand name and/ or model reference.
 
I bought a bunch of 7805s (all in one small plastic bag) which I
noticed some has different model reference. For eg. some have 7805 while
others have, 7805L. I would think the latter is low drop-out type. I
just want to be sure.
 
If normal 7805 requires an extra 1.5V from the source then, what extra
voltage is required for the low drop-out version ?
 
Thanks in advance for the help.
cheers,


National Semi make some common ones like the LP2940, LM2930 series
amongst dozens of others. A good place to start.
Many other companies make them too, like OnSemi, ST, LinearTech,
Fairchild and Zetex. They all have different numbers.

The 7805L labling could mean anything from "low dropout" to "low
power", you won't know unless you get the exact datasheet. Some numbers
may mean different things between different manufacturers.
LDO regulators can go down to only a few tens of millivolts above the
output, typically several hundred millivolts, depends on the current,
temperature and other factors, it is not a constant figure. Check the
graphs in the datasheet. Nor is it constant for the standard 7805, some
manufacturers are a lot better than others, some require closer to 3V
over the input voltage.
As I said, watch out, LDO regs are unstable by their very nature, they
can and do oscillate. Read the data sheet carefully and follow the
bypassing instructions. The 2940 for example must have a minimum amount
of output capacitance with a minimum ESR figure, otherwise ti will
oscilliate. Other brands and models can more stable.

Dave :)