Full Wave Rectifier - Definition, Working, FAQs

A full-wave rectifier is an electronic device that is used for rectifying the AC, into direct current DC. While the half-wave rectifier utilizes only one-half of the AC waveform, this is useful for most electronic devices that require a constant DC supply of power. In this article, we will discuss the full-wave rectifier along with its workings, advantages, and applications in detail.

Full-wave Rectifier

A full-wave rectifier is an electric circuit that is used to convert an Alternating current into Direct current. It uses both, the positive and the negative halves of the AC input signal hence it is more effective than the half-wave rectifier that just uses the positive half of the wave. Full-wave rectifiers are common in power supplies by converting AC voltage from the mains into DC voltage. It requires two junction diodes such that one diode rectifies one half and the second diode rectifies the second half of the input.

Working of Full-Wave Rectifier

A full-wave rectifier converts both halves of the alternating current into direct current. It can be designed using two configurations:

1. Center-Tapped Full-Wave Rectifier (two diodes and a center-tapped transformer)
2. Bridge Rectifier (four diodes arranged to form a bridge)

Let's discuss how these configurations work in detail.

Center-Tapped Full-Wave Rectifier

In this connection, a center-tapped transformer is used where the transformer has the secondary winding connected to a center-tapped. The center-tap is grounded and two diodes are used. Each diode conducts during different half cycles of the AC input.

Positive Half Cycle: During the positive half cycle one diode allows the current to flow through load resistor in single direction.

Negative Half Cycle: During the negative half cycle second diode will conduct and allows the current to flow through load resistor in same direction as positive half cycle.

Bridge Rectifier

In a bridge rectifier, four diodes are arranged to form a bridge, Hence, this arrangement does not require center-tapped transformer making it more efficient. During the positive half cycle, first two diodes will conduct and in the negative half cycle, the other two diodes will conduct. this results in current flowing through the load resistor in the same direction.

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Waveform of Full- wave rectifier

A full-wave rectifier produces an output waveform which is a pulsating DC. Ideally, the output in full-wave rectification would be a straight line DC but instead of this, the output will contain ripples. To minimize the ripple filtering techniques can be used.

Without filtering: The output will have a series of pulses, but the frequency of these pulses will be twice the input frequency (since both halves are utilised).

With filtering: A filter capacitor on the other hand regulates these pulses and comes up with a steady DC voltage.

Components of a Full-Wave Rectifier

Full-wave rectifier is composed of different components, which helps it to function properly. These components are duscussed below:

1. Diode: Diodes are semiconductors that allows the flow of current in one direction. Two diodes are used in case of Center-Tapped Full-Wave Rectifier and four in case of bridge rectifier.
2. Transformer(for center-tapped rectifier): It is used to step down or step up the AC voltage.
3. Load resistor (RL): This resistor is used to deliver the rectified output.
4. Filter capacitor (optional): It is used to smoothen the pulsating DC output and reduce ripples.

Formula Used in Full-Wave Rectifier

The following formulas are used in constructing a Full-wave rectifier; These formulas consists are discussed below:

1. Average Output Voltage (DC Voltage)

The average output voltage ( $V_{D C}$ ) is given by:

$$
V_{D C}=\frac{2 V_m}{\pi}
$$
Where:$V_m$ is the peak voltage across the secondary winding of the transformer.

2. RMS Value of the Output Voltage

The root mean square (RMS) value of the output voltage ( $V_{R M S}$ ) for a full-wave rectifier is given by:

$$
V_{R M S}=\frac{V_m}{\sqrt{2}}
$$

3. Efficiency

The efficiency $(\eta)$ of a full-wave rectifier is a measure of how much of the AC power is converted into $D C$ power. It is calculated as:

$$
\eta=\frac{P_{D C}}{P_{A C}}=\frac{V_{D C}^2}{V_{R M S}^2}=\frac{0.81}{1}=81.2 \%
$$
Where:
$P_{D C}$ is the DC power delivered to the load,
$\quad P_{A C}$ is the AC power supplied by the transformer.

4. Ripple Factor

The ripple factor $(\gamma)$ is a measure of the amount of $A C$ ripple present in the DC output. For a fullwave rectifier, it is calculated as:

$$
\gamma=\frac{I_{A C}}{I_{D C}}=\frac{1}{\sqrt{f}}
$$

5. Peak Inverse Voltage (PIV)

For a center-tapped full-wave rectifier, the peak inverse voltage (PIV) across each diode is equal to the peak voltage of the transformer secondary winding, $V_m$.

$$
P I V=V_m
$$

6. DC Output Power

The DC output power delivered to the load resistor $R_L$ is given by:

$$
P_{D C}=V_{D C} \times I_{D C}
$$
Where:
$I_{D C}$ is the average DC current, calculated as:

$$
I_{D C}=\frac{V_{D C}}{R_L}
$$

Advantages of Full-Wave Rectifier

• Higher Efficiency: Full-wave rectifiers make use of both the positive and the negative half cycles of the AC waveform and therefore are superior to half-wave rectifiers. The utilization factor of Full-wave rectifier is approximately 81.2 % while of half-wave rectifier is approximately 40.6 %.
• Smoother Output: The DC given out by a full-wave rectifier is smoother and contains less ripple than that given out by a half-wave rectifier thus ideal for use in use in the driving of delicate electrical circuits.
• Higher Average Output Voltage: Because of these two halves of the AC waveform being used, the average output voltage is higher in a full-wave rectifier than in the half-wave rectifier.
• Better Transformer Utilization: Compared with half-wave rectifier, full-wave rectifier make more efficient usage of the secondary winding of the transformer.

Disadvantages of Full-Wave Rectifier

• Complexity: Full-wave rectifiers require more diodes and are more difficult to design and fabricate in contrast to half-wave rectifiers.
• Transformer Requirements: The center-tapped Full-wave rectifier requires a center-tapped transformer, which may be expensive and large as compared to other transformers.
• Cost: Since full-wave rectifiers require additional diodes and use transformers besides, they could be slightly more costly than half-wave rectifiers.

Applications of Full-Wave Rectifiers

Full-wave rectifiers can be used in the power supply circuits of most electronic devices because they deliver more power in DC form than half-wave rectifiers. Some common applications include:

• Power Supplies for Electronic Circuits: Full-wave rectifiers are used in the power supply circuit of TV sets, Radios, computers, and any other electrical appliances you can think of.
• Battery Charging: They are used in charging batteries for various applications for a stabilizing charging current.
• Signal Demodulation: Full-wave rectifiers can be widely employed in the field of communication by demodulation of the signals.