@engr_joni_ee, we digress. Do you see that essentially the external transistors
are replicating the internal OpAmp output stage but with greater current capability
in their die construction, ie. power transistors versus small signal transistors current
capability ?
W/o getting too complicated when you boost a OpAmp output this way you can have
stability issues depending on nature of load, such as if its capacitive. Thats a whole
other discussion but essentially boils down to adding zeroes to loop response to
effectively reduce phase shift due to poles, internal and external, until loop gain is reduced
to < 1 when phase shift = 180 degrees thru the loop (added to OpAmp thru inverting input
adding 180 degrees due to its sign change). A phase shift total thru loop of 360 degrees
with a loop G >= 1 generally produces the following effect (below). Tons of info on web
on this topic.. That analysis is fairly simple thru s plane (LaPlace) analysis/algebra.
OpAmps are a whole world of fun to work with/analyze/use and are now ubiquitous in
design work, as are micros. Many micros now have 1 or more OpAmps onchip to signal
condition such things as onchip A/D's.......to create G blocks, to use as filters, to transform
signal properties, to manage non linear sensor behaviour........application areas simply huge.
Regards, Dana.
