How Diodes Work As a Rectifier - Half Wave Rectifier & Full Wave Rectifier

A rectifier will turn an AC power source into a DC power source and is due to the diode. Rectifier can be classified as half wave and full wave rectifier. Ripple factor of half wave rectifier can be calculated as the ratio of rms value of AC circuit to the rms value of DC circuit. A crystal diode may be used as the rectifier. This is one of the most useful ways of using diodes in any circuit and you will find them in pretty much every single circuit you look at especially power supply. In this article we will study in detail about what is rectification, rectifier circuit, rectifier diode, difference between half wave and full wave rectifier. What the ripple factor of half wave rectifier is? What the maximum efficiency of half wave rectifier is? Also about the efficiency of half wave rectifier and the efficiency of full wave rectifier.

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What is Diode?

A diode comes in different shapes and sizes. They normally have a black cylinder-shaped body as a band at one end as well as some leads coming out to permit us to connect it into a circuit. One end is known as the anode and other end is known as the cathode. A diode allows the current to flow in only one direction in a circuit from anode to cathode. Let us imagine a water pipe or the swing valve installed, as water flows through the pipe it will push the swing gate open and continue to flow through it. Though, if the water changes direction the water will thrust the gate shut and it will stop it from flowing. Thus water will only flow in individual direction. This is very alike to the use of diode in circuit, we practice them to regulate the direction of current in a circuit.

If we join a diode into a simple LED, we see that LED will individually turn on when the diode is connected in correct way and that's because it allows current to flow in one direction. So depending upon which way the diode is installed, the circuit will act as either a conductor or an insulator. In order for the diode to act as a conductor, the stripe end is connected to the negative and the black end is connected to the positive. This allows the current to flow, we call if forward bias. If we interchange the diode, it will turn into an insulator and current will not flow. We call this the reverse bias. We use copper wires as a conductor since copper has lot of free electrons which makes it easier to pass electricity through and We use rubber to insulate the copper wires and keep us safe because rubber is an insulator which means its electrons are held very closely and they can't move amongst atoms. Now let us understand rectifier working, rectifier efficiency and the types of rectifier (i.e. half wave rectifier and full wave rectifier)

Half Wave Rectifier:

In half wave rectifier ac power supply is connected with a single diode. So how many diodes are used in half wave rectifier? The answer is one diode. In half wave rectifier the supply of ac power source is connected to resistive load through a single diode. So in the positive half cycle is forward bias which means the diode is conducting. So since the diode is conducting we get an output for first positive half cycle. Now during the negative half cycle the diode is reverse bias. So in that case the diode will not conduct. Since there is practically no current flowing. We say that the diode is nonconducting and we get a zero output. Again during next positive half cycle the diode is conducting so we have output. During the next negative half cycle once again it will be in reverse bias and we have zero output. So the output is only in one direction. It is only in positive direction and there is no negative half cycle present. The output is now said to be rectified because it is only flowing in one direction. As only positive half cycle of the input wave is used it is known as half wave rectifier. Let us study the average and rms value of half wave rectifier.

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The average value of half wave rectified sine wave is given as:

V(s) = v(m) sinwt

Where v(m) = max. value of supply voltage.

V(m)=√2.V

Where V I = rms value of supply voltage.

V(dc)= average DC voltage across load

V(dc)=v(m)/= 0.318 v(m)

Average DC current through load:

I(dc)=average DC current through load

I(dc)=0.318 I(m)

Where I(m) = max. value of current

• Now, form factor is the ration of RMS value to the average value of the output power

F=RMS valueaverage value

The form factor for half wave rectified sine wave is equal to 1.57.

• Next is PIV (piv full form is pick inverse voltage of the half wave rectifier), the maximum voltage across the diode in the reverse direction. Which is equals to V(m)

• Ripple factor of the half wave rectification is 1.21

Ripple factor formula,

γ= VrRMSVdc

• Rectification efficiency of half wave rectifier is the ratio of output power to the input power. Maximum efficiency of half wave rectifier is equal to 40.6%.

Advantages of half wave rectifier: simple circuit, costs small, easy to practice and simple structure.

Disadvantages of half wave rectifier: utility factor is low, output voltage is low and high power loss.

Full Wave Rectifier:

In the full wave rectifier the AC power source is connected to load resistance through a transformer and two diodes. How many diodes are used in full wave rectifier? The answer is two diodes So full wave rectifier circuit using two diodes and the center transformer is shown in the figure below.

Both half cycles of the input are utilized with the help of two diodes working alternatively. Use of transformer is essential. In the half cycle the input current is transferred in the output current with the help of transformer. The output current flow through the diode D1 and RL resistive load in clockwise direction. So in positive half cycle the output voltage appear across RL is equal to the input voltage of the half cycle. In the negative half cycle the output current flow through diode D2 and resistive load RL in anticlockwise direction. So the output voltage across RL is the input voltage of negative half cycle but with opposite polarity. So current flowing through RL is in the same direction that is why the output voltage a across RL is in the positive direction only. Let us study the average and rms value of full wave rectifier.

NCERT Physics Notes:

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• Input signal is sinusoidal source and is given as:

V(s) = v(m) sinwt

Where v(m) = max. value of supply voltage.

V(m)=√2.V

Where V = rms value of supply voltage.

V(dc)= average DC voltage across load

V(dc)= 2v(m)/= 0.636 v(m)

Average DC current through load:

I(dc)=average DC current through load

I(dc)=0.626 I(m)

Where I(m) = max. value of current

Ripple factor of the full wave rectifier:

F=RMS valueaverage value

Which is equal to 1.11

• Next is PIV of diode (piv full form is pick inverse voltage of the half wave rectifier), the maximum voltage across the diode in the reverse direction. Which is equals to 2V(m).

• Ripple factor for the full wave rectifier is equals to 0.482

Ripple factor formula,

γ= VrRMSVdc

• Rectification efficiency of full wave rectifier is the ratio of output power to the input power. Rectification efficiency of full wave rectifier is equal to 81.2%.

Advantages of full wave rectifiers: high efficiency, low ripple factor and large output voltage.

Disadvantages of full wave rectifier: need two diodes, costlier and not suitable.

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