What is a Bridge Rectifier : Circuit Diagram & Its Working

The rectifier circuit is used to convert the AC (Alternating Current) into DC (Direct Current). Rectifiers are mainly classified into three types namely half-wave, full-wave, and bridge rectifier. The main function of all these rectifiers is the same as the conversion of current but they not efficiently convert the current from AC to DC. The center tapped full wave rectifier as well as bridge rectifier converts efficiently. A bridge rectifier circuit is a common part of the electronic power supplies. Many electronic circuits require a rectified DC power supply for powering the various electronic basic components from available AC mains supply. We can find this rectifier in a wide variety of electronic AC power devices like home appliances, motor controllers, modulation process, welding applications, etc. This article discusses an overview of a bridge rectifier and its working.

What is a Bridge Rectifier?

A Bridge rectifier is an Alternating Current (AC) to Direct Current (DC) converter that rectifies mains AC input to DC output. Bridge Rectifiers are widely used in power supplies that provide necessary DC voltage for the electronic components or devices. They can be constructed with four or more diodes or any other controlled solid-state switches.

Depending on the load current requirements, a proper bridge rectifier is selected. Components’ ratings and specifications, breakdown voltage, temperature ranges, transient current rating, forward current rating, mounting requirements, and other considerations are taken into account while selecting a rectifier power supply for an appropriate electronic circuit’s application.

Construction

The bridge rectifier construction is shown below. This circuit can be designed with four diodes namely D1, D2, D3 & D4 along with a load resistor (RL). The connection of these diodes can be done in a closed-loop pattern to convert the AC (alternating current) to DC (Direct Current) efficiently. The main benefit of this design is the lack of an exclusive center-tapped transformer. So, the size, as well as cost, will be reduced.

Once the input signal is applied across the two terminals like A & B then the o/p DC signal can be attained across the RL. Here load resistor is connected in between two terminals like C & D. The arrangement of two diodes can be made in such a way that the electricity will be conducted by two diodes throughout every half cycle. The pairs of diodes like D1& D3 will conduct electric current throughout the positive half cycle. Similarly, D2 & D4 diodes will conduct electric current throughout a negative half cycle.

Bridge Rectifier Circuit Diagram

The main advantage of the bridge rectifier is that it produces almost double the output voltage as with the case of a full-wave rectifier using a center-tapped transformer. But this circuit doesn’t need a center-tapped transformer so it resembles a low-cost rectifier.

The bridge rectifier circuit diagram consists of various stages of devices like a transformer, Diode Bridge, filtering, and regulators. Generally, all these blocks combination is called a regulated DC power supply that powers various electronic appliances.

The first stage of the circuit is a transformer which is a step-down type that changes the amplitude of the input voltage. Most of the electronic projects use a 230/12V transformer to step-down the AC mains 230V to 12V AC supply.

The next stage is a diode-bridge rectifier which uses four or more diodes depending on the type of bridge rectifier. Choosing a particular diode or any other switching device for a corresponding rectifier needs some considerations of the device like Peak Inverse Voltage (PIV), forward current If, voltage ratings, etc. It is responsible for producing unidirectional or DC current at the load by conducting a set of diodes for every half cycle of the input signal.

Since the output after the diode bridge rectifiers is of pulsating nature, and for producing it as a pure DC, filtering is necessary. Filtering is normally performed with one or more capacitors attached across the load, as you can observe in the below figure wherein smoothing of the wave is performed. This capacitor rating also depends on the output voltage.

The last stage of this regulated DC supply is a voltage regulator that maintains the output voltage to a constant level. Suppose the microcontroller works at 5V DC, but the output after the bridge rectifier is around 16V, so to reduce this voltage, and to maintain a constant level – no matter voltage changes in the input side – a voltage regulator is necessary.

Bridge Rectifier Operation

As we discussed above, a single-phase bridge rectifier consists of four diodes and this configuration is connected across the load. For understanding the bridge rectifier’s working principle, we have to consider the below circuit for demonstration purposes.

During the Positive half cycle of the input AC waveform diodes, D1 and D2 are forward biased and D3 and D4 are reverse biased. When the voltage, more than the threshold level of the diodes D1 and D2, starts conducting – the load current starts flowing through it, as shown in the path of the red line in the diagram below.

During the negative half cycle of the input AC waveform, the diodes D3 and D4 are forward biassed, and D1 and D2 are reverse biased. Load current starts flowing through the D3 and D4 diodes when these diodes start conducting as shown in the figure.

We can observe that in both cases, the load current direction is the same, i.e., up to down as shown in the figure – so unidirectional, which means DC current. Thus, by the usage of a bridge rectifier, the input AC current is converted into a DC current. The output at the load with this bridge wave rectifier is pulsating in nature, but producing a pure DC requires an additional filter like a capacitor. The same operation is applicable for different bridge rectifiers, but in the case of controlled rectifiers thyristors triggering is necessary to drive the current to load.

Types of Bridge Rectifiers

Bride rectifiers are classified into several types based on these factors: type of supply, controlling capability, bride circuit configurations, etc. Bridge rectifiers are mainly classified into single and three-phase rectifiers. Both these types are further classified into uncontrolled, half controlled, and full controlled rectifiers. Some of these types of rectifiers are described below.

Single Phase and Three Phase Rectifiers

The nature of supply, i.e., a single-phase or three-phase supply decides these rectifiers. The Single phase bridge rectifier consists of four diodes for converting AC into DC, whereas a three-phase rectifier uses six diodes, as shown in the figure. These can be again uncontrolled or controlled rectifiers depending on the circuit components such as diodes, thyristors, and so on.

Uncontrolled Bridge Rectifiers

This bridge rectifier uses diodes for rectifying the input as shown in the figure. Since the diode is a unidirectional device that allows the current flow in one direction only. With this configuration of diodes in the rectifier, it doesn’t allow the power to vary depending on the load requirement. So this type of rectifier is used in constant or fixed power supplies.

Controlled Bridge Rectifier

In this type of rectifier, AC/DC converter or rectifier – instead of uncontrolled diodes, controlled solid-state devices like SCR’s, MOSFET’s, IGBT’s, etc. are used to vary the output power at different voltages. By triggering these devices at various instants, the output power at the load is appropriately changed.

Bridge Rectifier IC

The bridge rectifier like RB-156 IC pin configuration is discussed below.

Pin-1 (Phase / Line): This is an AC input pin, where the connection of phase wire can be done from the AC supply toward this phase pin.

Pin-2 (Neutral): This is the AC Input pin where the connection of the neutral wire can be done from the AC supply to this neutral pin.

Pin-3 (Positive): This is the DC output pin where the positive DC voltage of the rectifier is obtained from this positive pin

Pin-4 (Negative /Ground): This is the DC output pin where the ground voltage of the rectifier is obtained from this negative pin

Specifications

The sub categories of this RB-15 Bridge rectifier range from RB15 to RB158. Out of these rectifiers, the RB156 is the most frequently used one. The specifications of the RB-156 bridge rectifier include the following.

• O/p DC current is 1.5A
• The maximum peak reverse voltage is 800V
• Output Voltage: (√2×VRMS) – 2 Volt
• The maximum input voltage is 560V
• Voltage drop for each bridge is 1V @ 1A
• The surge current is 50A

This RB-156 is most normally used compact, low cost and single phase bridge rectifier. This IC has the highest i/p AC voltage like 560V therefore it can be used for 1- phase mains supply in all countries. The highest DC current of this rectifier is 1.5A. This IC is the best choice in the projects for converting AC-DC and provide up to 1.5A.

Bridge Rectifier Characteristics

The characteristics of bridge rectifier include the following

• Ripple Factor
• Peak Inverse Voltage (PIV)
• Efficiency

Ripple Factor

The measurement of the output DC signal’s smoothness using a factor is called the ripple factor. Here, a smooth DC signal can be considered as the o/p DC signal including few ripples whereas a high pulsating DC signal can be considered as the o/p including high ripples. Mathematically, it can be defined as the fraction of ripple voltage and the pure DC voltage.

For a bridge rectifier, the ripple factor can be given as

Γ = √ (Vrms2/VDC)−1

The ripple factor value of the bridge rectifier is 0.48

PIV (Peak Inverse Voltage)

The peak inverse voltage or PIV can be defined as the highest voltage value that is coming from the diode when it is connected in reverse bias condition throughout the negative half cycle. The bridge circuit includes four diodes like D1, D2, D3 & D4.

In the positive half cycle, the two diodes like D1 & D3 are in the conducting position whereas both the D2 & D4 diodes are in the non-conducting position. Likewise, in the negative half cycle, the diodes like D2 & D4 are in the conducting position, whereas the diodes like D1 & D3 are in the non-conducting position.

Efficiency

The efficiency of the rectifier mainly decides how capably the rectifier changes AC (Alternating Current) into DC (Direct Current). The rectifier’s efficiency can be defined as; it is the ratio of the DC o/p power and AC i/p power. The bridge rectifier’s maximum efficiency is 81.2%.

η = DC o/p Power/AC i/p Power

Bridge Rectifier Waveform

From the bridge rectifier circuit diagram, we can conclude that the flow of current across the load resistor is equal throughout the positive & the negative half cycles. The polarity of the o/p DC signal may be either totally positive otherwise negative. In this case, it is totally positive. When the direction of the diode is reversed then a complete negative DC voltage can be attained.

Therefore, this rectifier allows the flow of current throughout both the cycles of positive as well as negative of the i/p AC signal. The bridge rectifier’s output waveforms are illustrated below.

Why is it Called Bridge Rectifier?

As compared with other rectifiers, this is the most efficient type of rectifier circuit. This is a type of full-wave rectifier, as the name suggests this rectifier uses four diodes which are connected in the bridge form. So this kind of rectifier is named a bridge rectifier.

Why do we Use 4 Diodes in Bridge Rectifier?

In the bridge rectifier, four diodes are used to design the circuit which will allow the full-wave rectification without using a center-tapped transformer. This rectifier is mainly used for providing full-wave rectification in most of the applications.

The arrangement of four diodes can be done within a closed-loop arrangement to change AC to DC efficiently. The main benefit of this arrangement is the nonexistence of the center-tapped transformer so that the size & cost will be decreased.

Advantages

The advantages of bridge rectifier include the following.

• The rectification efficiency of a full-wave rectifier is double that of a half-wave rectifier.
• The higher output voltage, higher output power, and higher Transformer Utilization Factor in case of a full-wave rectifier.
• The ripple voltage is low and of higher frequency, in case of full-wave rectifier so simple filtering circuit is required
•  No center tap is required in the transformer secondary so in the case of a bridge rectifier, the transformer required is simpler. If stepping up or stepping down of voltage is not required, the transformer can be eliminated even.
• For a given power output, a power transformer of a smaller size can be used in the case of the bridge rectifier because the current in both primary and secondary windings of the supply transformer flows for the entire ac cycle.
• Rectification efficiency is double as compared with a half-wave rectifier
• It uses simple filter circuits for high frequency and low ripple voltage
• TUF is higher as compared with a center-tapped rectifier
• Center tap transformer is not necessary

Disadvantages

The disadvantages of the bridge rectifier include the following.

• It requires four diodes.
• The use of two extra diodes causes an additional voltage drop thereby reducing the output voltage.
• This rectifier needs four diodes thus the rectifier’s cost will be high.
• The circuit is not appropriate once a small voltage is necessary to be rectified, because, the two diodes connection can be done in series & provides a double voltage drop because of their inner resistance.
• These circuits are very complex
• As compared with the center-tapped type rectifier, the bridge rectifier has more power loss.

An Application – Converting AC power to DC using a Bridge Rectifier

Regulated DC Power supply is often required for many electronic applications. One of the most reliable and convenient ways is to convert the available AC mains power supply into DC supply.  This conversion of the AC signal to DC signal is done using a rectifier, which is a system of diodes. It can be a half-wave rectifier that rectifies only one half of the AC signal or a full-wave rectifier that rectifies both cycles of the AC signal. The full-wave rectifier can be a center-tapped rectifier consisting of two diodes or a bridge rectifier consisting of 4 diodes.

Here the bridge rectifier is demonstrated. The arrangement consists of 4 diodes arranged such that the anodes of two adjacent diodes are connected to give the positive supply to the output and the cathodes of the other two adjacent diodes are connected to give the negative supply to the output. The anode and cathode of the other two adjacent diodes are connected to the positive of AC supply whereas the anode and cathode of another two adjacent diodes are connected to the negative of the AC supply. Thus 4 diodes are arranged in a bridge configuration such that in each half-cycle two alternate diodes conduct producing a DC voltage with repels.

The given circuit consists of a bridge rectifier arrangement whose unregulated DC output is given to an electrolyte capacitor through a current limiting resistor. The voltage across the capacitor is monitored using a voltmeter and keeps on increasing as the capacitor charges until the voltage limit is reached. When a load is connected across the capacitor, the capacitor discharges to provide the necessary input current to the load. In this case, a lamp is connected as a load.

A Regulated DC Power Supply

A regulated DC power supply consists of the following components:

• A step-down transformer to convert high voltage AC to low voltage AC.
• A bridge rectifier to convert the AC into pulsating DC.
• A filter circuit consisting of a capacitor to remove the AC ripples.
• A regulator IC 7805 to get regulated DC voltage of 5 V.

The step-down transformer converts the AC mains supply of 230V to 12V AC. This 12V AC is applied to the bridge rectifier arrangement such that the alternate diodes conduct for each half cycle producing a pulsating DC voltage consisting of AC ripples. A capacitor connected across the output allows the AC signal to pass through it and blocks the DC signal, thus acting as a high pass filter. The output across the capacitor is thus an unregulated filtered DC signal. This output can be used to drive electrical components like relays, motors, etc.  A regulator IC 7805 is connected to the filter output. It gives a constant regulated output of 5V which can be used to give input to many electronic circuits and devices like transistors, microcontrollers, etc. Here the 5V is used to bias a LED through a resistor.

This is all about the bridge rectifier theory its types, circuit, and working principles. We hope that this wholesome matter about this topic will be helpful in building students’ electronics or electrical projects as well as in observing various electronic devices or appliances. We appreciate your keen attention and focus on this article. And therefore, please do write to us for choosing the required component ratings in this bridge rectifier for your application and for any other technical guidance.

Now we hope that you have got an idea about the concept of the bridge rectifier and its applications if any further queries on this topic or the concept of the electrical and electronic projects leave the comments in the section below.

Photo Credits:

• Bridge rectifier by numato
• Uncontrolled Bridge Rectifiers by electronics-tutorials
• Controlled Bridge Rectifier by eng.cam
• Bridge Rectifier Circuit Diagram by engineersgarage
• Bridge Rectifier Operation by eniquest
• Bridge Rectifier Circuit and the output waveform by  neilorme