# op amp Op amp analysis question

Posted on Feb 6, 2014

The circuit was reverse engineered from an old equipment. The op amp stage seems to me like a comparator/oscillator, it is comparing \$V_0\$ which varies over time because of the capacitors against the 2. 5[V] that is a square wave generatorwith 5V amplitud. So is this an square wave oscillator or what What is its output your problem with simulation arises because SPICE calculates the operating point and

brings up the circuit in an ideal state. You can add some asymmetry into the circuit via a large 10Mohm to ground or rail, OR you can bump the non-inverting input with a voltage source 100 ns into the sim. Starrt it at say 5 v and then kick it to 2. 5V and it should light up if you have it connected properly. placeholder Jan 28 `13 at 2:25 Since each RC link entails a phase delay, at the frequency where the total phase shift is 180 °, there ought to be some positive feedback. What happens in your simulation if you start by force-feeding a 3 Hz square wave at the inverting input for a few seconds and then take it away Henning Makholm Jan 28 `13 at 2:41 The circuit is probably wrong, even though you have checked :-). You have 2 DC paths from U1A _out tp inverting input - one is 1. 5M and the other is 86. 2K (so precise). If it was positive feedback it would be interesting. Time constants are about 0. 1s. Overall it was either a rubbish circuit or intended to mislead or it has been reconstructed wrongly. | What is it part of Russell McMahon Jan 28 `13 at 2:43 @Russell McMahon: It is not 86. 2k but 56. 2k it was a measure straight from the Ohmeter. Ok, let`s suppose it is wrong and it is as you say but let`s concentrate on the given circuit arrangement (I`m open to suggestions and guesses of course). Can`t tell if rubbish or misleading, maybe the inputs of op-amp are inverted, but then again let`s concentrate on the current...

Leave Comment

characters left:

• ## New Circuits

.

Popular Circuits