8.5 Feedback

Outcome 5 of 12 in domain 8 · Systems, reading and designing a complete device

The loop that holds the whole device together, and why the op-amp of the course was only one case of it.

My targets

I declare:

Explain the closed loop: open-loop gain, loop gain, and what feedback buys (linearity, bandwidth, impedances) against what (gain).
Explain stability: phase, margin, and why an amp oscillates when the loop turns too far.
Spot the compensation (the Miller capacitor) on a schematic and say what it sacrifices.
Measure an amp’s response to a square wave and read the stability margin in the overshoot.
Recognize the same loop in a voltage regulator, a motor controller and a charger: feedback isn’t just audio.
Diagnosis: an amp that oscillates at high frequency, heats and whistles without signal, compensation, loop wiring or capacitive load; see it on the oscilloscope.