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Negative feedback is the process of feeding back to the input a part of a system's output, so as to reverse the direction of change of the output. This tends to keep the output from changing, so it is stabilizing and attempts to maintain homeostasis. When a change of variable occurs within a stable range, the system will attempt to establish equilibrium.
A simple example is a thermostat. When the temperature in a heated room reaches a certain upper limit the room heating is switched off so that the temperature begins to fall. When the temperature drops to a lower limit, the heating is switched on again. Provided the limits are close to each other a steady room temperature is maintained. The same applies to a cooling system, such as an air conditioner, a refrigerator, or a freezer.
'Positive' and 'negative' do not refer to desirability, but rather to the sign of the multiplier in the mathematical feedback equation. The negative feedback loop tends to bring a process to equilibrium, while the positive feedback loop tends to accelerate it away from equilibrium.
While it has some advantages,such as increased stability of the system, it also has disadvantages,like loss of gain.
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