Bridge Rectifier: Working, Properties & Diagram

Bridge rectifier is a type of full-wave rectifier that uses four or more diodes to convert alternating current (AC) to direct current (DC) efficiently. The three most common types of rectifiers include half-wave rectifiers, full-wave rectifiers, and bridge rectifiers. All these rectifiers work to convert AC into DC. However, not all these three rectifiers do the conversion process efficiently, only the center-tapped full-wave rectifier and bridge rectifier are able to efficiently convert the Alternating Current (AC) into Direct Current (DC).  

In electronic power supplies, a bridge rectifier circuit is a common component. A bridge rectifier is the most efficient circuit among different rectifiers. The power conversion in this device is very efficient. Bridge rectifiers are therefore a form of full wave rectifier that converts alternating (AC) current to direct (DC) current efficiently by using four or more diodes in a bridge circuit design.

Key Terms: AC power, DC power, Center-tapped transformer, Full wave Rectifier, Ripple Factor, Peak Inverse Voltage

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What is Bridge Rectifier?

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

• The purpose of the Bridge Rectifier is to efficiently convert AC power into DC power.
• Many electronic circuits require a rectified DC supply to power the electronic components from the available AC mains supply. 

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Construction of Bridge Rectifier

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The bridge rectifier or bridge full-wave rectifier circuit is made up of a load resistor R_L and four diodes D1, D2, D3, and D4.

• These four diodes are connected via a closed-loop configuration that efficiently converts the alternating current to a direct current. 
• Terminals A and B are applied with the input AC signal and the output DC signal is obtained across Resistor RL which is connected between M and L terminals. 
• The 4 diodes are connected in a way that only two diodes D1 and D3 conduct electric currents during the positive half cycle while D2 and D4 conduct electric current in the negative half cycle. 
• This change continue until the current keeps flowing.

The major advantage of bridge rectifier configuration is the reduction of size and cost as it can be used in the absence of an expensive center-tapped transformer.

Diagram showing construction of Bridge Rectifier

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Working of Bridge Rectifier

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When the input signal is applied across the bridge rectifier, the signal flows alternatively i.e. positive and negative cycle.

• During the positive half cycle, terminal B becomes negative and terminal A becomes positive.
• Therefore, as a result, diodes D1 and D3 become forward biased and D2 and D4 become reverse biased. 
• During the negative half cycle, B becomes positive and A becomes negative.
• Therefore, in the negative cycle, diodes D1 and D3 become reverse biased and D2 and D4 become forward biased. 
• The current flow across resistor R_L is the same during negative and positive half cycles.
• The polarity of the output DC signal may be completely positive or completely negative.
• If we reverse the direction of diodes, we can obtain a completely negative voltage. 

Working of Bridge Rectifier

Therefore, we notice that the flow of current across load resistor RL is the same during the positive as well as the negative half-cycles. The polarity of the output DC signal may be either completely positive or negative. Therefore, a bridge rectifier allows the electric current during both the positive and negative half cycles of the input AC signal. The input and output waveforms of the bridge rectifier can be shown as –

Bridge rectifier waveform

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Properties of Bridge Rectifier

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The different characteristics of bridge rectifier are as follows – 

Ripple Factor

Ripple Factor can be explained as smoothness of output DC signal.

Ripple Factor Diagram

• The output DC signal having fewer ripples can be considered a smooth DC signal.
• Whereas a DC signal having more ripples can be considered a pulsating DC signal.
• The ripple factor can be defined as a ratio of ripple voltage to pure DC voltage. 

The formula for ripple factor is:

\(\gamma = \sqrt{{V_{rms}^2 \over V_{DC}} -1}\)

• V_rms = Root Mean Square Voltage
• V_DC = Average Voltage of DC Supply

The ripple factor for a Bridge rectifier is considered to be 0.48.

Bridge Rectifier Efficiency

The efficiency of a Bridge Rectifier can be simply understood as to how efficiently the bridge rectifier converts AC to DC. The efficiency of the Bridge Rectifier can be taken as the ratio of DC output power to AC input power. 

Ideally, the efficiency of the Bridge Rectifier can be taken as 81.2%.

The formula for Bridge Rectifier Efficiency is:

η = \({{DC\ Output\ Power} \over {AC\ Output\ Power}}\)

Peak Inverse Voltage

Peak Inverse Voltage can be defined as the maximum voltage that a diode can endure in reverse biased conditions. 

Peak Inverse Voltage Diagram

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Advantages and Disadvantages of Bridge Rectifier

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Bridge rectifiers have become widely available because of their low cost, high reliability, and small-sized silicon diodes. 

Advantages

The advantages of a bridge rectifier are – 

• Bridge Rectifier has higher efficiency than a half-wave rectifier. A bridge rectifier has efficiency equivalent to that of a center-tapped full-wave rectifier.
• The bridge rectifier has a smoother output signal in comparison to the output DC signal of a half-wave rectifier. 
• Unlike a half-wave rectifier, the flow of current is allowed during both negative and positive cycles. This makes the output DC signal almost equal to the input AC signal.

Disadvantages

Bridge Rectifier has the following disadvantages – 

• It has a complex circuit consisting of 4 different diodes.
• Bridge Rectifier has a large power loss.

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Things to Remember

• The rectifier is an electrical device that converts an Alternating Current into a Direct Current. Bridge Rectifier is one of the categories of Rectifier.
• Definition: Bridge Rectifier is an efficient rectifier circuit that converts input AC supply to DC supply.
• The benefit of using a bridge rectifier: Minimal size and cost.
• Circuit Components: Four diodes, resistor, AC power supply 
• Efficiency: η=DC Output Power/AC Output Power

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