9 Difference Between Positive And Negative Feedback In Control System

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A feedback system is one in which the output signal is sampled and then fed back to the input to form an error signal that drives the system. Feedback systems are very useful and widely used in amplifier circuits, oscillators, process control systems as well as other types of electronic systems. Whereas there are many different types of control systems, there are just two main types of feedback control:

  • Negative feedback
  • Positive Feedback

Positive Feedback Systems

In a positive feedback control system, the set point and output values are added together by the controller as the feedback is ‘’in-phase’’ with the input. The effect of positive feedback is to increase the systems gain i.e the overall gain with positive feedback applied will be greater than the gain without feedback.

What You Need To Know About Positive Feedback

  1. When a system uses positive feedback, then it increases the effective input of the system by adding the actual input with the feedback signal.
  2. Positive feedback is also referred to as regenerative feedback.
  3. The phase shift offered by positive feedback circuit is either 0o or 360o.
  4. A positive feedback is less stable.
  5. In positive feedback, the input and output signals are of similar phase and therefore the two signals get added.
  6. In the op-amp circuits, the non-inverting input terminal is used to provide positive feedback to it.
  7. The overall gain of the system that incorporates positive feedback is more than the gain of the system in the absence of feedback.
  8. The sensitivity offered by positive feedback system is lesser than a negative feedback system.
  9. Positive feedback is used in oscillators

Negative Feedback System

 Negative feedback also referred to as balancing feedback occurs when some function of the output of a system, process or mechanism is fed back in a manner that tends to reduce the fluctuations in the output, whether caused by changes in the input or by other disturbances. The effect of negative feedback is to reduce the gain. Negative feedback produces stable circuit responses, improves stability and increases the operating bandwidth of a given system. An example of a negative feedback system is an electronic amplifier based on an operational amplifier.

What You Need To Know About Negative Feedback

  1. When a system uses negative feedback, then it decreases the overall input of the system by subtracting the feedback signal from the actual applied input.
  2. Negative feedback is also referred to as degenerative feedback.
  3. The phase shift in negative feedback circuit is 180o.
  4. A negative feedback is more stable.
  5. In negative feedback, the input and output signals are of different phases thus the two signals are subtracted.
  6. In the op-amp circuits, the inverting input terminal is used to provide negative feedback.
  7. The overall gain with the system possessing negative feedback is less than the gain of the system with no feedback.
  8. The sensitivity offered by negative feedback system is more than a positive feedback system.
  9. Negative feedback is used in amplifiers.

Also Read: Difference Between Combinational And Sequential Circuit

Difference Between Positive And Negative Feedback In Tabular Form

BASIS OF COMPARISON POSITIVE FEEDBACK NEGATIVE FEEDBACK
Synonym Positive feedback is also referred to as regenerative feedback. Negative feedback is also referred to as degenerative feedback.
Effect When a system uses positive feedback, then it increases the effective input of the system by adding the actual input with the feedback signal.   When a system uses negative feedback, then it decreases the overall input of the system by subtracting the feedback signal from the actual applied input.  
Phase Shift The phase shift offered by positive feedback circuit is either 0o or 360o.   The phase shift in negative feedback circuit is 180o.  
Stability A positive feedback is less stable.   A negative feedback is more stable.  
Input & Output Signals In positive feedback, the input and output signals are of similar phase and therefore the two signals get added.   In negative feedback, the input and output signals are of different phases thus the two signals are subtracted.  
op-amp circuits In the op-amp circuits, the non-inverting input terminal is used to provide positive feedback to it.   In the op-amp circuits, the inverting input terminal is used to provide negative feedback.  
Overall Gain The overall gain of the system that incorporates positive feedback is more than the gain of the system in the absence of feedback.   The overall gain with the system possessing negative feedback is less than the gain of the system with no feedback.  
Sensitivity The sensitivity offered by positive feedback system is lesser than a negative feedback system.   The sensitivity offered by negative feedback system is more than a positive feedback system.  
Application Positive feedback is used in oscillators   Negative feedback is used in amplifiers.  

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