Thanks Paul. I looked through the LM1117 circuit and
found that there is an error amp used in it. The error
amp from my understanding acts as a voltage
comparator. When the comparator detects a higher
voltage than the reference it allows current to pass
through from the main NPN therefore regulating the Vo
from the voltage regulator. I have implement a similar
circuit on LTSpice and it works very well. Still am
marvelling the ingenuity of LM1117. 


Thanks,
John

--- Paul Hutchinson <paullhutchinson@yahoo.com> wrote:

> > -----Original Message-----
> > From: piclist-bounces@mit.edu On Behalf Of John
> Chung
> > Sent: Thursday, August 31, 2006 11:46 AM
> >
> > I have messing around with LM1117. From my
> experience it is 
> > a good regulator. The thing I like about it is the
> voltage 
> > regulation. When the circuit is open the voltage
> reads 
> > 5.00volts. When I place the load which is a PIC
> with 
> > blinking led the voltage drops only to 4.99
> volts*with 
> > voltage input ranging from 9v to 18volts!*. This
> is 
> > remarkable to my standards. So my question is, can
> we build 
> > a voltage regulator with such good voltage
> regulation?
> 
> I know I could design and build a voltage regulator
> circuit that meets the
> 0.2% combined line/load regulation that you are
> seeing. However, the circuit
> will cost 10+ times more than an LM1117. The high
> cost to make your own is
> why I haven't designed a linear voltage regulator
> since the late 1980's.
> 
> > I have been playing with zeners and diodes and
> managed to 
> > get a +- 0.05 volts with load and varies voltage
> input*9 
> > volts to 18 volts*.
> 
> That's pretty good performance (1%) for a simple
> zener based regulator. To
> get significantly better line/load regulation you'll
> need to start with a
> precision voltage reference instead of a zener and
> use op-amps to provide
> the output and isolate the reference from the load.
> 
> Paul
>  
> >
> > Thanks,
> > John
> 
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