Op-amps & voltage regulators
An op-amp is a differential amplifier with absurdly high gain. It multiplies the tiny difference between its two inputs by 100,000 or more. Raw, that gain is useless, since any real input slams the output into a supply rail. The fix is negative feedback. Route a fraction of the output back to the inverting input and the op-amp continuously adjusts its output to keep the two inputs equal. Now a couple of resistors set the exact gain.
Two rules of thumb describe an ideal op-amp with feedback: the inputs draw no current, and the output does whatever it takes to make the inputs match. From those two rules you can work out amplifiers, filters, buffers, and integrators on paper. Take the feedback away and the same part becomes a comparator, driving its output high or low depending on which input is greater.
A voltage regulator applies the same feedback idea to power. It compares its output against an internal reference and corrects continuously, holding a steady 3.3 V or 5 V while the input sags and the load jumps around. Nearly every board has at least one, because digital chips want a stable rail and raw input power from batteries, USB, or adapters is never as clean as it claims.
Key points
- Op-amps have enormous raw gain. Negative feedback tames it so resistors set the behavior.
- Ideal op-amp rules: no current into the inputs, and the output acts to make both inputs equal.
- Without feedback an op-amp is a comparator, a one-bit answer to which input is bigger.
- Regulators hold a rail steady against input and load changes. Sensitive chips depend on one.
Practice
0 of 2 answered · Not startedWrong answers just let you try again, and hints are there if you want them. Answering every question first time, without hints, is what earns mastery.
- 1
What do the op-amp "golden rules" assume in a circuit with negative feedback?
- 2
What does an LDO regulator do with the voltage difference between its input and output?
