Negative feedback

From The Book of THoTH (Leaves of Wisdom)

Negative feedback (shortened to NFB) 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 constant conditions.

1 Explanation
2 Examples
3 NFB in electronic amplifiers
- 3.1 Advantages
- 3.2 Disadvantages
4 See also
5 External links

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Explanation

The term 'negative' do not refer to desirability, but rather to the sign of the multiplier in the mathematical feedback equation. When a change of variable occurs, a negative feedback system will attempt to re establish equilibrium.

Negative feedback is used in this way in many types of amplification systems to stabilise and improve their amplification characteristics (see e.g., operational amplifiers).

While it has many advantages, such as increased stability of the system, NFB also has disadvantages, like loss of gain.

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Examples

A simple and practical 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.

Some biological systems exhibit negative feedback such as the baroreflex in blood pressure regulation and erythropoiesis. Many biological process (e.g., in the human anatomy) use negative feedback. Examples of this are numerous, from the regulating of body temperature, to the regulating of blood glucose levels. The disruption of negative feedback can lead to undesirable results: in the case of blood glucose levels, if negative feedback fails, the glucose levels in the blood may begin to rise dramatically, thus resulting in Diabetes.

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