Bridge Rectifier - Definition, Factor, Efficiency and ...

A Bridge Rectifier is an electronic device that is used for converting alternating current into direct current. It is a type of non-linear electronic rectifier. In this article, we are going to learn about the Bridge Rectifier, its characteristics, advantages, disadvantages, etc. So, without any further ado, let us start by understanding a Bridge Rectifier: 

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What is a Bridge Rectifier?

The Bridge Rectifier is said to be a widely used circuit among many electronic circuits. Bridge Rectifiers are widely used for supplying power to various electronic basic components. 

The purpose of the Bridge Rectifier is to convert the AC power into DC power. It is the most resourceful rectifier circuit from others. The power conversion in this device is very efficient. We call it a Bridge Rectifier, as it makes a bridge-like circuit by including 4-diodes. 

To improve the output of the Bridge Rectifier, a filter is also used inside the circuit. Let’s learn about the Bridge Rectifier in brief, especially about Bridge Rectifier working, its efficiency, and so forth.

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Bridge Rectifier Circuit

The Bridge Rectifier includes four diodes, such as D1, D2, D3, D4. It also includes a load resistor RL. To make its performance more efficient, these four diodes are linked in a closed-loop configuration. 

Then, it converts the AC (alternating current) into DC (direct current). The non-existence of the exclusive centered-tapped transformers makes the configuration of this device more relevant. It helps to reduce the cost and size of the device.

The diagram given below shows the circuit diagram of the Bridge Rectifier:

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Point-A and Point-B are the terminals where the input signal is applied. Point-C and Point-D are the output terminals that produce DC signals across the load resistor RL. The arrangement of four diodes is made in a unique fashion. That is why only two diodes conduct electricity throughout every half cycle.

The diodes that pair to conduct electricity through the positive half cycle are D1 and D3. Similarly, the diode pairs D2 and D4 conduct electricity during the negative half cycle.

Bridge Wave Rectifier

The following figure shows the current flow during the positive half-cycle:

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The following figure shows the current flow during the negative half cycle:

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Now, we will discuss how a Bridge Rectifier works:

If you supply the power (AC) across the Bridge Rectifier, the terminal–A turns into positive, and the terminal–B turns into negative during the positive half cycle. At this point, the diodes D1 and D3 get changed into forward biased, whereas D2 and D4 turn into reverse biased.

Terminal-A becomes positive, and terminal–B becomes negative during the negative half-cycle. At this point, the diodes D1 and D3 change into reverse-biased, whereas D2 and D4 turn into forward-biased.

The above figures show that the flow of current across the load resistor RL remains the same during the positive half-cycles and the negative half-cycles. The polarity of the output DC signal may vary completely. Output may be negative or positive completely.

Bridge Rectifier Waveform

We acquire a complete negative DC voltage when the diodes’ direction is reversed. That is why electric current can pass through a Bridge Rectifier during both negative and positive half-cycles of the AC input signal.

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Characteristics of Bridge Rectifier

The characteristics of Bridge Rectifier are:

• Ripple factor of the Bridge Rectifier

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• Peak inverse voltage

• The efficiency of the Bridge Rectifier

Ripple Factor of Bridge Rectifier

The ripple factor is a feature associated with the Bridge Rectifier that measures the smoothness of the output DC signal. We can say the output DC signal is a smooth output when it comes to fewer ripples. The high pulsating DC signal is measured as the high ripples.

The expression for the ripple factor is explained as the ratio of ripple voltage to the pure DC voltage.

Mathematically,

\[\gamma = \sqrt{\frac{V_{rms}^{2}}{V_{DC}} - 1}\]

\[V_{rms} = \text{Root Mean Square Voltage}\]

\[V_{DC} = \text{Average Voltage of DC Supply}\]

Peak Inverse Voltage

The maximum voltage that a diode can withstand under reverse bias conditions is called the peak reverse voltage. During the positive half cycle, the diodes D1 and D3 are in a conducting state, while D2 and D4 are in a non-conducting state. Similarly, during the negative half cycle, the diodes D1 and D3 are in a  non-conducting state, and the diodes D2 and D4 are in a conducting state.

The Efficiency of Bridge Rectifier

The measurement of the efficiency of the Bridge Rectifier shows the optimum performance of the rectifier. The definition of rectifier efficiency is the ratio of the DC output power to the AC input power.

\[\eta = \frac{\text{DC Output Power}}{\text{AC Output Power}}\]

Note: A Bridge Rectifier has a maximum efficiency of 81.2%.

Advantages of Bridge Rectifier

Here are some advantages of Bridge Rectifier:

1. A Bridge Rectifier has a higher efficiency than a half-wave rectifier. But sometimes, the efficiency of the center-tapped full-wave rectifier and the Bridge Rectifier is the same.

2. A smooth output is obtained from a Bridge Rectifier than the half-wave rectifier.

3. The Bridge Rectifier allows both positive and negative half cycles of the input AC signal for processing. This feature is not found in the half-wave rectifier, and processes only half of the AC signal, blocking the other.

Disadvantages of Bridge Rectifier

Here are some points regarding the disadvantages of Bridge Rectifiers:

• If compared to a half-wave rectifier and a center-tapped full-wave rectifier, the circuit of a Bridge Rectifier is more complicated.

• It uses four diodes to convert the AC current to DC, whereas the center-tapped full-wave rectifiers use only two diodes.

• There is more power loss when diodes are used multiple times.

• A higher voltage drop is sensed in the Bridge Rectifiers.

Peak Inverse Voltage of a Bridge Rectifier

A peak inverse voltage is a maximum voltage that a diode can endure in the reverse bias condition. The diodes D1 and D3 are in the conducting state in the positive half, and the diodes D2 and D4 are in the non-conducting state.

However, in the negative half, the diodes D2 and D4 are in the conducting state, and the diodes D1 and D3 are in the conducting state.

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I found a circuit where in the classical Graetz rectifier capacitors were added in parallel to each diode.

It looked something like this:

After the rectifier itself, there was the usual huge capacitor and regulator and so on.

So why the smaller capacitors near the diodes?

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