Full Wave Rectifier: Circuit, Working, Formula, Advantages and Disadvantages

A full wave rectifier is an important electronic circuit that changes alternating current (AC) into direct current (DC). Many electronic devices such as chargers, televisions, and power supplies, use this circuit to get a steady flow of current. You might have observed that most electronic devices work on DC even though our homes receive an AC supply. A full wave rectifier makes this possible by converting both halves of the AC signal into a useful DC output.

This article gives a detailed explanation of the full wave rectifier, its circuit, working, formulas, advantages, and disadvantages.

Table of Contents

• What is Full Wave Rectifier
• Different Types of Full Wave Rectifiers
• Important Formulas of Full Wave Rectifier
• Advantages of a Full Wave Rectifier
• Disadvantages of a Full Wave Rectifier

What is Full Wave Rectifier

A full wave rectifier is an electronic circuit that converts alternating current (AC) into direct current (DC) by using both the positive and negative halves of the AC signal. Since the entire AC cycle is used, the output is smoother and more efficient than that of a half-wave rectifier.

In simple words, a full wave rectifier changes AC into pulsating DC and allows current to flow through the load in only one direction.

Interestingly! A full wave rectifier can be made in two ways,

• Using a centre-tapped transformer and two diodes.
• Using four diodes connected in a bridge arrangement.

Because of its better performance and reduced ripples, the full wave rectifier is widely used in power supplies, battery chargers, and many electronic devices.

Different Types of Full Wave Rectifiers

A full wave rectifier can be designed in more than one way, but the main purpose remains the same: to convert both halves of an AC signal into DC. Based on the circuit arrangement and the number of diodes used, full wave rectifiers are mainly divided into two types: 

• Centre-Tapped Full Wave Rectifier
• Bridge Full Wave Rectifier

Let us study each type in detail.

Centre-Tapped Full Wave Rectifier

A centre-tapped full wave rectifier uses a centre-tapped transformer, two diodes, and a load resistor to convert alternating current (AC) into direct current (DC).

The secondary winding of the transformer has a connection at its centre, dividing the AC voltage into two equal parts. The two diodes are connected to the ends of the secondary winding, while the load resistor is connected to the centre tap.

During the positive half cycle of the input AC, one diode becomes forward-biased and conducts current, while the other diode remains reverse-biased and does not conduct.

During the negative half cycle, the roles of the diodes change. The diode that was conducting turns off, and the other diode starts conducting. As a result, current flows through the load in the same direction during both half cycles.

Interestingly! Since both halves of the AC signal are used, the output of a full wave rectifier is smoother and more efficient than that of a half-wave rectifier.

Working of Centre-Tapped Full Wave Rectifier

The working of a centre-tapped full wave rectifier can be explained in two steps,

• Positive Half Cycle: Diode  D1 is forward-biased and conducts current, while diode  D2 remains reverse-biased. Current flows through the load resistor.
• Negative Half Cycle: Diode  D2 becomes forward-biased and starts conducting, while diode  D1 turns off. Current again flows through the load in the same direction.

Because both halves of the input AC are converted into DC, the output voltage is continuous and has fewer ripples compared to a half-wave rectifier.

Centre-Tapped Full Wave Rectifier Formula

The average DC output voltage of a centre-tapped full wave rectifier is given by,

VDC=2Vmπ

 

where:

•   VDC = Average output DC voltage
•   Vm = Peak value of the input AC voltage
• π=3.14

The output current is given by,

IDC=VDCRL

 

where,

•    IDC= Average DC current
•   RL = Load resistance

Do you know? The average output voltage of a full wave rectifier is almost twice that of a half-wave rectifier, which makes it more efficient for power supply circuits.

Bridge Full Wave Rectifier

A bridge full wave rectifier is a type of full wave rectifier that converts alternating current (AC) into direct current (DC) without using a centre-tapped transformer. It uses four diodes connected in a bridge arrangement to rectify both halves of the input AC signal.

The four diodes are arranged in such a way that two diodes conduct during one half cycle of the input AC, while the other two conduct during the next half cycle. As a result, current always flows through the load in the same direction, producing a pulsating DC output.

Since both halves of the AC signal are used, a bridge rectifier provides a smoother output and higher efficiency than a half-wave rectifier.

Working of the Bridge Full Wave Rectifier

The working of a bridge full wave rectifier can be explained with the help of the input and output waveforms shown above.

Positive Half Cycle

During the positive half cycle of the input AC voltage, two of the four diodes become forward-biased and allow current to flow through the load resistor. The other two diodes remain reverse-biased and do not conduct.

Negative Half Cycle

During the negative half cycle, the conducting and non-conducting diodes interchange their roles. The other pair of diodes now becomes forward biased and allows current to pass through the load.

Interestingly! Even though different pairs of diodes conduct during each half cycle, the current through the load always flows in the same direction.

The input waveform is a sinusoidal AC signal that changes from positive to negative repeatedly. After rectification, both the positive and negative half cycles are converted into positive pulses, producing a pulsating DC output.

As shown in the output waveform, the frequency of the rectified output is twice the frequency of the input AC signal. Because both halves of the AC signal are used, the bridge rectifier provides a smoother output and higher efficiency than a half-wave rectifier.

Do you know? Since a bridge rectifier uses all parts of the input waveform and does not require a centre-tapped transformer, it is widely used in power supplies, battery chargers, and electronic devices.

Important Formulas of Full Wave Rectifier

Moving ahead, let us look at some important formulas related to a full wave rectifier.

Quantity	Formula	Description/Value
DC Output Voltage	(Vdc=2Vmπ)	(Vm) is the peak voltage.
RMS Value of Current	(Irms=Im2)	(Im) is the peak current.
Peak Inverse Voltage (PIV)	(PIV=2Vm)	Applicable for a centre-tapped full wave rectifier.
Form Factor	Form Factor=VrmsVdc	Value = 1.11
Peak Factor	(Peak Factor=VmVrms)	Value = 1.41
Rectification Efficiency	(η=PdcPac×100)	Maximum efficiency = 81.2%

The rectification efficiency of a full wave rectifier is almost twice that of a half-wave rectifier, making it more efficient for converting AC into DC. 

Advantages of a Full Wave Rectifier

A full wave rectifier offers several advantages because it uses both halves of the AC cycle to produce DC output. Some of its important advantages are:

• Higher Efficiency: It has an efficiency of about 81.2%, which is much higher than that of a half wave rectifier.
• Lower Ripple Factor: The output contains fewer ripples, resulting in smoother DC.
• Higher Output Voltage and Power: Since both halves of the AC cycle are used, the output voltage and power are greater.
• Easier Filtering: The ripple frequency is higher, making it easier to obtain a steady DC output using filters.
• Better Transformer Utilisation: The transformer is used more effectively, improving overall performance.

Interestingly! These advantages make full wave rectifiers widely used in power supply circuits and electronic devices.

Disadvantages of Full Wave Rectifier

Although a full wave rectifier is more efficient than a half-wave rectifier, it also has some limitations.

• More Components: A bridge rectifier uses four diodes, making the circuit more complex.
• Higher Cost: A centre-tapped full wave rectifier requires a special transformer, which increases the cost.
• Voltage Drop: In a bridge rectifier, current passes through two diodes at the same time, causing a voltage drop.
• Higher PIV Requirement: The diodes in a centre-tapped rectifier must withstand a high peak inverse voltage (PIV).
• Needs Filtering: The output is still pulsating DC and often requires a filter circuit to obtain a smoother DC output.

The fact is that despite these disadvantages, full wave rectifiers are widely used because of their high efficiency and better performance.

A full wave rectifier is an important electronic circuit that converts alternating current (AC) into pulsating direct current (DC) by using both halves of the input AC signal. Compared to a half-wave rectifier, it provides higher efficiency, a smoother output, and lower ripple content, making it more suitable for practical applications