Feedback System

In a Feedback System, all or part of the output signal is fed back into the input, positively or negatively.

BackNotification Systems process signals and are therefore signal processors.The processing part of a feedback system can be electrical or electronic, ranging from very simple to very complex circuits.

Simple analogue backusing separate or separate components such as notification control circuits, transistors, resistors and capacitors, etc., or using more complex digital backcan be created using microprocessor-based and integrated circuits (IC's) to create notification systems.

As we can see, open loop systems are open-ended only, and no attempt is made to compensate for changes in circuit conditions or changes in load conditions due to changes in circuit parameters such as gain and stability, temperature, feed voltage. variations and/or external disturbances.But the effects of these "open loop" variations can be eliminated or at least significantly reduced by the introduction of feedback .

Backthe notification system is the system in which the output signal is sampled and then fed back into the input to generate an error signal that runs the system.In the previous tutorial about Closed Loop Systems, you canwe found that the notification consisted of a sub-circuit that allowed part of the output signal from a system to change the active input signal to generate a response. this may differ significantly from the response generated in the absence of such feedback.

Feedback Systems are very useful and are widely used in amplifier circuits, oscillators, process control systems and other types of electronic systems.But feedback needs to be checked to be an effective tool, because an uncontrolled system either oscillates or does not work.The basic model of a feedback system is given as follows:

Feedback System Block Schema Model

Feedback System

This basic backdrepa, consisting of detection, control, and operationnotification loop, a backnotification is the main concept behind the control system andThere are several good reasons for implementing and using the declaration:

  • Circuit features such as system gain and response can be precisely controlled.
  • Circuit features can be made independent of operating conditions such as feeding voltages or temperature changes.
  • Signal distortion can be greatly reduced due to the nonlinear structure of the components used.
  • Frequency Response, Gain, and Bandwidth of a circuit or system can be easily controlled within strict limits.

Although there are many different types of control systems, only two main backThere is a type of notification control: Negative Feedback and Positive Feedback .

Positive Feedback Systems

A "positive back"notification control system", backthe setting point and output values are added together by the controller because the notification is in the "same phase" as the input.Positive (or regenerative) backthe effect of the notification is to "increase" the system gain, that is, the positive back appliedtotal earnings with notification, backwill be larger than the gain obtained without notice.For example, if someone praises you or gives you positive feedback about something, you feel happy and full of energy about yourself, you feel more positive.

However, there is a lot of praise and positive feedback in electronic and control systemsnotification can increase the gain of systems too much, which will lead to oscillation circuit responses as it increases the size of the active input signal.

Positive backan example of notification systems can be an electronic amplifier based on a transactional amplifier or op-amp as shown.

Positive Feedback System

Feedback System

Op-amp's positive backnotification control is also achieved by applying a small part of the output voltage signal Vout inverting (to back + backnotification resistant, with) R F to the input terminal.

If the input voltage is Vin positive, the op-amp strengthens this positive signal and the output is more positive.Some of this output voltage is restoredis returned to the input by the notification network.

Thus, the input voltage becomes more positive and causes an even larger output voltage, and this continues.He's finally out, positive.becomes saturated on the notification track.

Similarly, if the input voltage is Vin negative, the opposite happens, and the op-amp is saturated on the negative feed rail.Then we can see that positive feedback does not allow the circuit to function as an amplifier, since the output voltage quickly fills up on one feeding track or another, since the positive backWith notification loops, "more paths lead to more" and "fewer paths lead to less" .

If the cycle gain for any system is positive then the transfer function will be: Av = G / (1 – GH).Note if you want to make GH = 1 system gain Av = infinity and circuit an oscillator, it is useful that no input signal will start to oscillate from itself after that, which is necessary to be able to sustain oscillations.

Although it is often seen as undesirable, this behavior is used in electronics to achieve a very fast switching response to a condition or signal.Positive backAn example of notification usage is hysteresis, in which a logic device or system maintains a certain state until some inputs cross a predetermined threshold.This type of behavior is called "two-stability" and is often associated with digital switching devices such as logic gates and multivibrators.

We found that positive or regenerative feedback increases the likelihood of gain and instability in a system that can lead to self-releases, and therefore, positive feedback is widely used in oscillation circuits such as Oscillators and Timing circuits .

Negative Feedback Systems

A "negative back"notification control system", backthe setting point and output values are subtracted because the notification is "out of phase" with the original input.The effect of negative (or degenerative) feedback is to "reduce" gain.For example, if someone criticizes you or gives you negative feedback about something, you feel unhappy about yourself, and therefore if your energy drops, you feel less positive.

Negative backbecause the notification produces stable circuit responses, improves stability, and increases the working bandwidth of a particular system, all control and backmost notification systems are degenerative, reducing the effects of gain.

A negative backan example of the notification system is an electronic amplifier based on a transactional amplifier, as shown.

Negative Feedback System

Feedback System

The amplifier's negative backnotification control allows a small portion of the output voltage signal in the Vout to benotification resistance is ensured by applying the inverter ( – ) to the input terminal via RF.

If the input voltage is Vin positive, the op-amp amplifies this positive signal, but the output is more negative because it depends on the inverter input of the riser.Some of this output voltage is restoredthe notification is returned to the input by the network Rf.

Thus, the input voltage, negative backreduces the notification signal, causing an even smaller output voltage, and so on.As a result, the output will remain at a value determined by the RF ÷ Rin earnings ratio and become stable.

Similarly, if the input voltage is Vin negative, the opposite happens, and the op-amp output is positive (inverted), which is added to the negative input signal.Then we can see that negative feedback allows the circuit to function as an amplifier, as long as the output is within saturation limits.

Thus, the output voltage is stabilized andwe can see that it is controlled by the notification, because negative backWith notification loops, "more paths lead to less" and "fewer paths lead to more".

If the cycle gain for any system is positive then the transfer function will be: Av = G / (1 + GH) .

Use negative back amplifier and back for process control systemsnotification systems positively restoreA more stable rule than notification systems is that it is common as a negative and if there is no oscillation alone at any frequency other than, it is said that a negative feedback system is stable in a specific circuit state.

Another advantage is that negative feedback also makes control systems more immune to random changes in component values and inputs.Of course nothing is free, so negative backthe notification should be used with caution as it significantly changes the operating characteristics of a particular system.

Classification of Feedback Systems

So far we have seen how the output signal is "fed back" into the input terminal andFor notification systems, this can be Positive Feedback or Negative Feedback.However, the way the output signal is measured and placed on the input circuit can be very different, leading to four basic feedback classifications.

Depending on the amount of inlets strengthened and the desired output condition, the input and output variables can be modeled as voltage or current.As a result, the single loop back, where the output signal feeds back into the inputThere are four basic classifications of the notification system, and these are:

  • Series-Shunt Configuration – Voltage input and Voltage output or Voltage Controlled Voltage Source (VCVS).
  • Shunt-Shunt Configuration – Current input and Voltage output or Current Controlled Voltage Source (CCVS).
  • Series-Series Configuration – Voltage input and Current output or Voltage Controlled Current Welding (VCCS).
  • Shunt Series Configuration – Current input and Current output or Current Controlled Current Welding (CCCS).

These names are backit comes from the way the notification network connects between the input and output stages, as shown.

Serial-Shunt Feedback Systems

Series-Shunt Feedback, also known as serial voltage feedback, is a voltage-voltage controlled feedbackas a notification system.Backthe error voltage fed back from the notification network is serial with input.The voltage fed back from the output is proportional to the output voltage, since vo is parallel or shunt-connected.

Serial-Shunt Feedback System

Feedback System

The configuration for serial shunt connection is defined as Vin, output voltage, Vout input voltage.Most inverter and non-inverting operational amplifier circuits produce what is known as a "voltage amplifier"notification.Ideal input resistance as a voltage amplifier, Rin is very large and the ideal output resistance, Rout is very small.

Then "serial-shunt backnotification configuration", the input signal works as a voltage and the output signal is a voltage, so the transfer gain is given as follows: Av = Vout ÷ Vin .Note that this amount is dimensionless because its unit is volt/volt.

Shunt Series Feedback Systems

Shunt Series Feedback, also known as shunt current feedback, is a current-controlled feedbackas a notification system.The feedback signal is proportional to the Io output current flowing in the load.Backthe notification signal is fed back parallel to the input or shunt, as shown.

Shunt Series Feedback System

Feedback System

For shunt series connection, configuration output current is defined as Iin from Iout to input current.In the shunt-series feedback configuration, the feedback signal is parallel to the input signal and therefore parallel to currents, not added voltages.

This parallel shunt feedback connection will not normally affect the voltage gain of the system, since a voltage input is required for a voltage output.In addition, the serial connection at the output increases the output resistance, the shunt connection in the Rout input reduces the input resistance, Rin .

Then, since the input signal is a current and the output signal is a current, the "shunt-series feedback configuration" works as a real current amplifier, so the transfer gain is given as follows: Ai = Iout ÷ Iin .Note that this amount is dimensionless because its unit is amperage/amperage.

Series-Series Feedback Systems

Series-Series Feedback Systems, also known as serial current feedback, operate as a voltage-current controlled feedback system.In the serial current configuration, the feedback error signal is serial with input and the load current is proportional to Iout.In fact, this type of feedback turns the current signal into a voltage that actually feeds back, and this is the voltage that is removed from the input.

Serial-Serial Feedback System

Feedback System

The configuration for serial connection is defined as output current, input voltage Iout, Vin.The output current of the serial connection increases both the input and output impedances of the system as it feeds Iout back in voltage.Therefore, the circuit works best as a transconduction amplifier with ideal input resistance, Rin is very large and the ideal output resistance Rout is also very large.

Then, since the input signal is a voltage and the output signal is a current, the "series-series feedback configuration" acts as a transconducting type amplifier system. then the transfer gain for a series-series feedback circuit is given as follows: Gm = Iout ÷ Vin .

Shunt-Shunt BackNotification Systems

Shunt-Shunt Feedback Systems, also known as shunt voltage feedback, operate as a current-voltage controlled feedback system.In the shunt-shunt feedback configuration, the feedback signal is parallel to the input signal.The output voltage is detected and the current is removed from the input current in the shunt and therefore is removed from the currents, not the voltages that come out.

Shunt-Shunt Feedback System

Feedback System

For shunt-shunt connection, configuration output voltage is defined as Iin to Vout input current.Since the output voltage is fed back into a current-oriented input port, the shunt connections in both the input and output terminals reduce the input and output impedance.Therefore, the system works best as a transition resistance system with ideal input resistance, Rin is very small and the ideal output resistance, Rout is also very small.

Then the shunt voltage configuration works as a transducer voltage amplifier because the input signal is a current and the output signal is a voltage, so the transfer gain is given as follows: Rm = Vout ÷ Iin

Summarize

A BackDepending on the type of feedback used, the Notification System is fed back into the input to sample the output signal and then generate an error signal that runs the systemwe found that it is a system in which the notification signal is confused with the system. the system can be input signal, voltage or current.

Backnotification will always change the performance of a system andnotification arrangements are either positive (regenerative) or negative (degenerative) type backnotification systems.Back around the systemIf the notification cycle produces a loop gain that is negative, feedback is said to be negative or degenerative, and the main effect of negative feedback is to reduce system gain.

However, if the gain around the cycle is positive, the system is said to have positive feedback or refresher feedback.The effect of positive feedback is to increase the gain, which can cause a system to become unstable and oscillating, especially if it is GH = -1.

Back various block diagramsnotification systems can also be used to show.In the above block diagrams, input and output variables can be modeled as voltage or current, and therefore possible backThere are four input and output combinations representing notification types, namely: Serial Voltage Feedback, Shunt Voltage Feedback, Serial Current Feedback, and Shunt Current Feedback.

This is a different type of backthe names of the notification systems are derived from the way that the feedback network connects in parallel (shunt) or serially between the input and output stages.

BackIn the next lesson on notification systems, we will look at the effects of Negative Feedback on a system and see how it can be used to improve the stability of a control system.