Positive feedback is a type of feedback. Open systems (ecological, biological, social) contain many types of regulatory systems, among which are systems that involve positive feedback and its relative negative feedback. When a change of variable occurs in a system, the system responds. In the case of positive feedback the response of the system is to change that variable even more in the same direction. This has a de-stabilizing effect, so left unchecked, does not result in homeostasis. In some cases (if not controlled by negative feedback), a positive feedback loop can run out of control, and can result in the collapse of the system.

Positive and negative do not mean or imply desirability. The negative feedback loop tends to slow down a process, while the positive feedback loop tends to speed it up. Positive feedback is used in certain situations where rapid change is desirable.

Positive feedback in electrical engineering

Feedback is well understood and widely studied in electrical engineering. Whereas negative feedback is used to stabilize the response of an electrical system and reduce nonlinear effects, positive feedback is often used to take advantage of these nonlinear effects (for example, the Schmitt trigger), or at least is used with the understanding that nonlinear effects, not feedback, will limit the output (in oscillators, and in popular configurations for MESFET amplifiers). An important consideration in the design of feedback amplifiers is to avoid unintentionally creating positive feedback (see frequency compensation).

See also

• Donella Meadows' twelve leverage points to intervene in a system
• stability criterion