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Ripple factor is known to be the ratio of the RMS Value of an Alternating Current element in the rectified output to the average value of rectified output.
- Ripple is the fluctuation within the output of the rectifier.
- Therefore, this factor is significant to measure the rate of fluctuation within the resolved output.
- The ripple inside the output voltage can be reduced by using filters such as capacitors.
- Most circuits, such as rectifiers, use a capacitor in parallel with a thyristor or diode to act as a filter in the circuit.
- This capacitor helps reduce ripple within the rectifier output.
Read More: Unit of Voltage
Key Terms: Ripple, Ripple Factor, Half-Wave Rectifier, Full-Wave Rectifier, Bridge Rectifier, AC Component, Current, Direct Current
What is Ripple?
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Ripple is the fluctuating AC component that is present in rectified DC output. The output of a rectifier can be either a DC current or voltage.
The AC fluctuating component present in DC output voltage is known as voltage ripple and that in DC current output is known as current ripple. Likewise, the ripple current is an AC component within the o/p current.
What is Ripple Factor?
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The ripple factor is the ratio of the RMS value of an alternating current element in the rectified output to the average value of rectified output.
The ripple factor is denoted as γ. It is a dimensionless quantity. It always has a value less than unity.
Ripple factor, γ = RMS value of AC component in rectifier outputAverage value of rectifier output
Thus,
γ = I’rms/Idc = V’rms/Vdc
In the above equation,
- I’rms is the alternating component of load current
- V’rms is the alternating component of voltage
![Ripple Factor Diagram]()
Ripple Factor Diagram
Read Also: Types of Circuit
Why Ripple Occurs?
There is no possibility to get exact DC output whenever rectification is done by the rectifier circuit.
Some variable AC components often occur at the output of a rectifier. A rectifier circuit can be made with a diode or a thyristor.
The ripple mainly depends on the elements used in the circuit.
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Ripple Factor Formula
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The ripple factor formula is described in terms of the RMS value and the average value of the rectifier output. It is given as follows:
Ripple Factor Derivation
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From the definition of ripple factor, we know that there are two parameters that are to be decided:
- The RMS value of the ripple present in the rectifier output current or output voltage.
- The average value of the output of the rectifier over a period of time, T.
Ripple is the distinction between the actual output and the expected DC output. The mathematical equation is:
Ripple = iL – Idc
= vL – Vdc
Here,
- iL = output current
- vL = output voltage
- Idc = average value of the load current
- Vdc = the average value of the load voltage
The RMS value of voltage ripple is given by:
However, we understand that the effective value of the load current is provided as:
Therefore,
The RMS value of ripple is given as,
The average value is given as:
The second integration will be equal to Idc:
But ωt = T
Therefore,
We understand that the ripple factor is the ratio of the RMS value and the average value of the rectifier output, which is provided as:
Significance of Ripple Factor
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The significance of Ripple factor is:
- The output of a single-phase rectifier is not purely DC. It also has some AC components. The ripple value defines the AC elements.
- The magnitude of the AC component within the output is characterized by a ripple issue.
- A high value of the ripple factor indicates that the output of the rectifier has a large AC component.
Read Also: Types of Current
Rectifier
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Rectifier circuits are the most common circuits used in electronics because almost every electronic device runs on DC (direct current), but DC is not always available.
Rectifiers are ideal for converting AC to DC in enterprises and at home. Rectifiers are also used in our cell phone chargers to convert AC to DC from our home outlets.
Ripple Factor of Half Wave Rectifier
From the ripple factor formula, we understand that
Shuffling the above equation, we have the ripple factor of half wave rectifier as:
Ripple Factor of Full Wave Rectifier
From the formula of the ripple factor, we understand that
Replacing the values, we have the ripple factor of the full-wave rectifier as follows:
Ripple Factor of Bridge Rectifier
The ripple factor of a bridge rectifier is similar to the ripple factor of a full-wave rectifier, namely:
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Ripple Frequency
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Ripple frequency is the frequency of the residual AC voltage after rectification to DC in the power supply.
- The ripple frequency depends on the rectifier we use.
- For a half-wave rectifier, its input frequency or supply frequency is 50Hz and the ripple frequency for a half-wave rectifier is the same as the supplied frequency, which is 50Hz.
- In a normal ripple, the frequency is twice the input frequency.
- For a full-wave rectifier, its input frequency is 60Hz and hence its ripple frequency is 120Hz.
Effect of Ripples
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Some equipment can work with ripples, while some sensitive test equipment and audio devices do not work properly with high-ripple operating supplies. The ripple effects are as follows:
- It heats up and damages the capacitor
- Negatively impacts sensitive instrumentation
- Interferes with TV displays
- Causes noise to audio circuits
- Leads to errors in digital circuits, incorrect outputs in logic circuits, and data corruption.
Read Also: Digital Electronics and Logic Gates
How to Overcome Ripple?
We can remove the ripples in the rectified output by introducing filters.
- One way is to introduce capacitors, which are smoothing capacitors that convert the ripple voltage into a smooth DC voltage.
- Aluminum electrolytic capacitors are widely used for this purpose and with a capacity of 100uF or more.
- A DC pulse charges the capacitor to a peak voltage. Factors to consider when choosing a capacitor are voltage and capacitance value.
- A lower value of capacitance will not be productive and capacitors may be connected in parallel to raise the value.
- Most good power supplies have a ripple of better than 10mV RMS.
Things to Remember
- Ripple is the fluctuating AC component that is present in rectified DC output.
- The ripple factor is the ratio of the RMS value of an alternating current element in the rectified output to the average value of rectified output.
- The ripple factor formula,
- A high value of the ripple factor indicates that the output of the rectifier has a large AC component.
- The ripple frequency depends on the rectifier we use. We can remove the ripples in the rectified output by introducing filters.
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Sample Questions
Ques. What is a Zener Diode? (1 mark)
Ans. A semiconductor device that operates under the reverse bias in the breakdown region is known as a Zener diode.
Ques. What is Potential Barrier? (1 mark)
Ans. The potential distribution near the p-n junction is referred to as the potential barrier.
Ques. Explain the function of a p-n junction diode as a half-wave rectifier. (India 2014) (2 Marks)
Ans. AC voltage to be rectified is connected to the primary coil of a step-down transformer and the secondary coil is connected to the diode via a resistor RJ, from which the output is obtained.
Working: The p-n junction is forward-biased during the positive half cycle of the input AC. Thus, the resistance in the p-n junction decreases, and current flows. So, we get the output in the load.
During the negative half cycle of the input AC, the p-n junction is reverse-biased. Thus, the resistance of the p-n junction increases, and the current does not flow. Hence, there is no output to the load. Therefore, for a complete cycle of AC, current flows through the load resistance in the same direction.
Ques. Why must a photodiode be operated at reverse bias? (1 Mark)
Ans. Photodiodes are used to detect optical signals. In the case of a reverse-biased diode, the fractional change in a minority carrier can be more easily measured than that of the forward-biased diode. Hence the photodiode is operated at reverse bias.
Ques. Explain the formation of a depletion region in a junction diode. (Delhi 2011) (2 Marks)
Ans. With the formation of a p-n junction, holes from the p-region diffuse into the n-region and electrons from the n-region diffuse into the p-region and the electron-hole pairs combine and annihilate.
This input creates a potential barrier, VB across the junction that opposes further propagation through the junction. Thus, small regions are formed around the junction which is depleted of free charge carriers and contains only stable ions called depletion regions.
Ques. Both carbon and silicon have four valence electrons, so how do they differ? (Delhi 2011) (2 Marks)
Ans. The four valence electrons of carbon are present in the second orbital while that of silicon is in the third orbital. Therefore, the energy required to remove electrons from silicon is much smaller than carbon.
Therefore, unlike carbon, the number of electrons free for conduction in silicon is significant. This makes the conductivity of silicon much higher than that of carbon. This is the main distinctive property.
Ques. Why is the current under reverse bias almost independent of the applied potential up to a critical voltage? (3 Marks)
Ans. Under reverse bias conditions, holes on the p-side are attracted to the negative terminal of the battery, and electrons on the n-side are attracted to the positive terminal of the battery.
This increases the depletion level and potential impedance. However, minority charge carriers flow across the junction producing a small current.
At any temperature, the number of minority carriers is constant, so there is a small current at any applied potential. This is because the current under reverse bias is almost independent of the applied potential. At a critical voltage, an avalanche breakdown occurs which results in a sudden flow of large current.
Ques. Why does the reverse current show a sudden increase at the critical voltage? (3 Marks)
Ans. At a critical voltage, holes in the n-side and conduction electrons in the p-side are accelerated due to the reverse bias voltage. These minority carriers gain enough kinetic energy from the electric field and collide with the valence electrons.
Thus, the bond eventually breaks and the valence electron moves into the conduction band resulting in an enormous flow of electrons and thus, the formation of hole-electron pairs. Thus, there is a sudden increase in current at the critical voltage. A Zener diode is a semiconductor device that functions under the reverse bias in the breakdown area.
Ques. Explain the formation of a p-n junction in brief. (3 Marks)
Ans. With the formation of a p-n junction, holes from the p-region diffuse into the n-region and electrons from the n-region diffuse into the p-region and the electron-hole pairs combine and annihilate.
This input creates a potential barrier, VB across the junction that opposes further propagation through the junction. Thus, small regions are formed around the junction which is depleted of free charge carriers and contain only immobilized ions called depletion regions.
Ques. Define the function of Light Emitting Diodes (LEDs). (2 Marks)
Ans. An LED is a forward-biased p-n junction that converts electrical energy into optical energy in the infrared and visible light regions.
Being in forward bias, a thin depletion layer and low potential barrier facilitate diffusion of electron and hole via the junction when high energy electron of the conduction band connects with the low energy holes in the valence band, then energy is released in the form of a photon, may be noticed in the form of light.
Ques. (i) How is a depletion region formed in the p-n junction?
(ii) How do you get a stable DC output from a pulsating voltage? (Delhi 2013) (5 Marks)
Ans. (i) A p-n junction is an arrangement made by the close contact of an n-type semiconductor and a p-type semiconductor. There are various methods of making a p-n junction diode.
In one method, n-type germanium crystals are cut into thin pieces called wafers. An aluminium film is deposited on an n-type wafer which is then heated in an oven at about 600°C. The aluminium is then diffused into the surface of the wafer. Thus, a p-type semiconductor is formed on an n-type semiconductor.
Formation of the depletion region in p-n junction: The concentration of electrons is greater than the concentration of holes in an n-type semiconductor. In a p-type semiconductor, the concentration of holes is greater than the concentration of electrons.
- During the formation of the p-n junction and because of the concentration gradient across p and n-sides, electrons diffuse from n-side to p-side (n —> p), and holes diffuse from p-side to n-side (p—> n).
- The diffused charge carriers combine with their counterparts near the junction and neutralize each other. Thus, near the junction, a positive charge is built up on the n-side and a negative charge on the p-side.
- This sets up a potential difference across the junction and an internal electric field Ej directed from the n-side to the p-side.
- Equilibrium is established when the field £ becomes strong enough to prevent further diffusion of the majority charge carriers (however, it helps the minority charge carriers to diffuse across the junction).
- The region on either side of the junction that is depleted (free) of mobile charge carriers is called the depletion region or depletion layer. The width of the depletion region is 10-6 m.
- The potential difference developed in the depletion region is called the potential barrier. The potential barrier depends on the dopant concentration in the semiconductor and the junction temperature.
(ii) A full-wave bridge rectifier using four diodes (full-wave bridge rectifier) gives a constant, unidirectional but pulsating output voltage or current.
The rectified output is passed through a filter circuit that removes the ripple and a nearly constant DC voltage (or current) is obtained.
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