Quick questions on Feedback in control systems explained: O-Level Electronics Systems and Signal Processing

In negative feedback, the fed-back signal opposes change: it acts to reduce the error and bring the output back towards the set value. This makes a system stable and self-regulating. A thermostat uses negative feedback: if the room is too cold the heater turns on, and if it is too warm the heater turns off, so the temperature is held steady around the set point. Negative feedback is also what gives an op-amp amplifier its stable, controlled gain.

In positive feedback, the fed-back signal reinforces change: it pushes the output further in the direction it is already moving. This drives a system rapidly to one extreme rather than holding it steady, which is useful for switching cleanly between two states but unsuitable for steady regulation. Most control systems that must hold a value steady use negative feedback.