I have implemeneted an external error amp with this 12V, 10A buck converter with an op amp (U3) followed by an NPN (Q1).
The error amplifier feedback is taken into the "non-inverting input" of the op amp due to the fact that the NPN (Q1) does an inversion.
Is this OK?......i always thought negative feedback had to go to the inverting input of the error amp?
(the error amp is external as this buck will be paralleled with ten other bucks all feeding the same 100A load...just one error amp feeds all controllers)
You know spice. Do a frequency sweep of two error amplifiers. (inverting and non-inverting The non-inverting amplifier can not have a gain less than 0db. The inverting amp will have a high gain at DC and low frequencies and the gain will hit zero at the same spot but continue negative.
It is inverting if the phase shift through the amp is 180 degrees, as you already assume. Since the transistor inverts the output of the op amp it needs to go to the +ve input to be stable, i.e. total phase shift 180 (I am ignoring the phase shift introduced by the passives for simplicity).