> various components. On op amps, I use the "theory of the happy op amp"
> that assumes the two input voltages are the same. Determine the voltage at
> the non-inverting input, assume the inverting input is the same, and
> analyze from there.
> =

> Good luck!
> =

> Harold
> =


The eye opener with op amps for me was when I realized that as long as the =

positive input is at a higher voltage than the negative, the output wants t=
o go =

high (all the way to the rail if it can) and the output wants to go low if =
the =

positive input is at a lower voltage than the negative. If the inputs are =

connected correctly, the feedback network won't allow this to happen since =
the =

voltage on one of the inputs (or perhaps both) is affected by the op amps =

output making the output stabilaze at the voltage that results in both inpu=
ts =

having the same voltage. From here on it is simply ohms law to calculate th=
e DC =

gain and the output voltage given the input voltage.

Another eye opener in visualizing EMC and emitted radiation on a circuit bo=
ard =

is that all electrons pushed out (or sucked in) by a power supply or driver =

through a circuit needs to have exactly the same amount of electrons return=
 to =

it. Keeping these current loops as small as possible won't let the currents =

wander around all over the circuit board, possibly by capacitive coupling, =

creating fields and voltage drops. If the current needs to travel a long wa=
y, =

make sure that the return current can run close to the output current to ev=
en =

out the fields created by them. Thinking like this also helps visualize cur=
rent =

paths in high voltage applications (like 10kV or more) where electrons are =

sucked in or pushed out of emitters in order to create air ions. An electro=
n =

can only leave the circuit if another one can be brought in, hopefully thro=
ugh =

a dedicated, low ohm earth connection and hopefully not through capacitive =

coupling against an earth plane or other conductor. Capacitive coupling goe=
s a =

long way with high voltages.

/Ruben

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D
Ruben J=F6nsson
AB Liros Electronic
Box 9124, 200 39 Malm=F6, Sweden
TEL INT +46 40142078
FAX INT +46 40947388
ruben@pp.sbbs.se
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D
-- =

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