Difference between Positive Feedback and Negative Feedback

The control system is an important component in engineering and technology. It involves many different mechanisms to improve or regulate the systems. The primary goal of the control system is to manage the input to get the desired output from the system. There are two types of control systems: open-loop control systems and closed-loop control systems. The open-loop control system can operate without any feedback, but the closed-loop control system can operate with the output of the system sent to its input as feedback. Feedback is an important concept in control systems; it plays a major role in different factors by providing accuracy, and stability, and improving the performance of various engineering and technical applications. It uses the output of the system to perform its operations by creating a closed loop. In control systems, positive feedback and negative feedback are mechanisms that influence the system’s behavior.

In this article, we will be going through the Differences between Positive Feedback and Negative Feedback, First, we will see what is Feedback, Then we will go into brief about Positive Feedback and Negative Feedback, Then we will go through the Difference between positive and Negative Feedback in the Tabular Form, At last, we will conclude our Article with Some FAQs.

What is Feedback?

Feedback in a control system is the process of sending some portion of the output signal back to the input of the system. Then it creates a closed loop, which allows the system to continuously monitor and adjust its behavior. This feedback can be used in industrial applications. By using this feedback in any control system, we can achieve accuracy and good stability for its entire operation. The feedback contains internal sensors that measure the actual output of the system. We can discuss this positive and negative feedback in detail. In control systems, positive feedback and negative feedback are mechanisms that influence the system’s behavior. There are two types of feedback signals in the control system, namely: Positive feedback and Negative feedback.

Positive Feedback

Positive Feedback

The input signal is the sum of the actual signal, and the feedback signal is known as positive feedback. The above figure shows the circuit diagram for positive feedback. The positive feedback can be used to amplify system responses. The major drawback of this positive feedback is its instability. These can be used less in traditional control systems as compared to negative feedback. Positive feedback can actually add the feedback to its input, whereas negative feedback subtracts. For example, we can find positive feedback in a microphone and speaker system. The microphone picks up sound, amplifies it through the speakers, and captures it again. Here, it creates a loop, increasing amplification.

The Transfer Function of Positive FeedBack can be Written as:

[Tex]TF=\frac{G}{1-GH} [/Tex]

Advantages of Positive Feedback

• Positive feedback is mainly used for amplification. Positive feedback can amplify weak signals.
• Positive feedback is well-used in non-linear systems such as oscillators or amplifiers.
• In applications where quicker responses to changes in input are needed, we use positive feedback.

Disadvantages of Positive Feedback

• It is very difficult to control and regulate a system with positive feedback.
• The amplification effect of positive feedback can result in unstable system behaviour or even system failure.
• It is very challenging to maintain system stability.

Applications of Positive Feedback

• Positive feedback can be used in regenerative amplifiers to increase the amplitude of signals.
• Positive feedback can be used in oscillators to produce oscillations and in electronic circuits.
• These can be used in biological processes during a child’s birth; they can intensify the labour process.
• This can be used in robotics and automation.
• Positive feedback can also be used to control the audio systems.

Negative Feedback

Negative Feedback

The input signal of negative feedback is the difference between the original input and the feedback signal. The main advantage of negative feedback is its stability; it can reduce discrepancies between the desired output signal and the actual output signal. Negative feedback can be used more in control systems as compared to positive feedback. By using this, we can minimise errors, and it ensures consistent performance under varying conditions. These can be well used in applications like amplifiers, medical applications, and speed control applications. The perfect example of negative feedback is the regulation of blood glucose levels in human body. When glucose levels deviate from the set point, the pancreas releases insulin to lower them. As glucose levels approach the set point, insulin release decreases, maintaining a stable blood glucose level. The above figure shows the circuit diagram for negative feedback.

The Transfer Function of Negative FeedBack can be Written as:

[Tex]TF=\frac{G}{1+GH} [/Tex]

Advantages of Negative feedback

• Negative feedback maintains good system stability by preventing uncontrollable oscillations.
• The system is very reliable with the use of negative feedback.
• Negative feedback can resist external disturbances by keeping the system secure.

Disadvantages of Negative feedback

• One of the major disadvantages of negative feedback is its slower response.
• It provides good stability, but the response will be slower.
• There is an energy loss in negative feedback systems. Implementing negative feedback is complex.

Applications of Negative feedback

• The negative feedback can be used in temperature controls in HVAC systems to maintain a comfortable temperature.
• Negative feedback can be used in speed control in vehicles in cruise control mechanisms.
• This can be used in amplifiers for audio systems.
• Aircraft use negative feedback to maintain dynamic stability.
• Negative feedback can be used in an audio equilizing system to adjust the frequency response.

Difference between Positive Feedback and Negative Feedback

Positive Feedback	Negative Feedback
Positive feedback is also called as regenerative feedback.	Negative Feedback is also called as degenerative feedback
The system gain of the positive feedback is high	The system gain of the negative feedback is low.
The Stability of positive feedback is less	The Stability of negative feedback is Comparatively more
The phase shift of positive feedback is 00 or 3600	The phase shift of negative feedback is 1800
Feedback is taken from Non-inverting terminal of an op-amp	Feedback is taken from Inverting terminal of an op-amp
Transfer Function of positive feedback is TF = G/1-GH	Transfer Function of negative feedback is TF = G/1+GH
Sensitivity of positive feedback is Low	Sensitivity of negative feedback is High
The positive feedback can be used in oscillators	The negative feedback can be used in Amplifiers

Conclusion

In conclusion, both positive and negative feedback mechanisms play a major role in control systems because of their individual characteristics and applications. When it comes to its usage, positive feedback is conventionally less in use because of its instability, whereas negative feedback can be used very popularly due to its stability and accuracy. These negative feedbacks can be used in vast applications, such as medical applications, speed control of vehicles, amplifiers, and temperature controls. It has the ability to maintain steady and accurate performance even in disturbances, making it widely used in industrial and engineering applications. Even though it has some disadvantages, like low noise amplification, limited bandwidth, and reduced sensitivity, it is also having many challenges in its delay operations. While negative feedback can be a more powerful system, one should consider it in control systems.

In essence, the combination of positive and negative feedback mechanisms allows for a comprehensive approach to the design of control systems by calculating the requirements and achieving optimal system behaviour.

FAQs on Positive Feedback and Negative Feedback

Can a system have both positive and negative feedback?

Yes, some systems incorporate both positive and negative feedback mechanisms.

What is feedback?

It is a process of sampling and returning the output to the input side of the system.

What are G and H?

G is the open-loop gain of the system. H is the gain feedback path.

Does feedback affect bandwidth?

Feedback will not affect bandwidth; it increases the bandwidth and also improves the input and output impedances of the system.