What is Rectifier? Explanation, Types & FAQs

Rectifiers

The electricity supply that reaches our homes from power grids is alternating current, but the electric appliances commonly used in our homes require direct current. The process of conversion of alternating current to direct current is called rectification. Conversion of AC current to DC is preceded by a further process that involves filtering the current and DC to DC conversion. One of the commonest parts of an electric power supply is a bridge rectifier. 

A lot of electronic circuits are dependent on the DC power supply for the functioning of basic components of electronic devices. This DC is rectified from the available main supply of alternating current. A rectifier circuit converts currents instead of voltages. 

What is the rectifier definition?

Rectifier definition: What is rectifier? A rectifier is an electronic device used for converting alternating current to direct current with the help of one or more p-n junction diodes. It acts as a one-way valve allowing the current to flow in one direction only. This process by which a diode acts as a rectifier is called rectification. A rectifier can exist in several physical shapes like diodes in the solid state, diodes of the type vacuum tube, valves of mercury-arc, rectifiers that are silicon-controlled, and various other semiconductor switches that are silicon-based.

What is rectifier working? A rectifier works by using switches that can be of various types. Broadly switches are of two types— controllable and uncontrollable. Any given rectifier that has a configuration of diodes not fully under the control of the operator is called an uncontrollable rectifier. Such a type of rectifier does not let the current alter on the basis of the load requirement. It is most commonly used in constant or fixed power supplies.

Types of Rectifiers

There are two main types of rectifiers— uncontrolled and controlled.

Controlled rectifiers: These are the types of rectifiers whose voltage can be changed. To convert an uncontrolled rectifier into a controlled rectifier, MOSFETs, IGBTs, or SCRs are used. These are more desirable than their uncontrolled counterparts. Controlled rectifiers are of two types– Half wave and full wave rectifiers of controlled variety. Half-wave controlled rectifiers are similar in design to the half-wave uncontrolled rectifiers, but the dioder is replaced with an SCR.

Uncontrolled rectifiers: As the name suggests, the voltage of uncontrolled rectifiers cannot be controlled. These are further of two types– half wave rectifier and full wave rectifier. A half-wave rectifier is a type of rectifier that changes only a half-cycle of the altering current into a direct current. On the other hand, a full-wave rectifier changes both the negative and positive half cycles of the alternating current into direct current. Four diodes are used in a bridge rectifier that is linked in the form of a Wheatstone bridge.

Bridge Rectifier Definition

Bridge rectifiers are classified into many types on the basis of many factors, including their type of supply, controlling capacity, and the configuration of the bridge circuit. Broadly, bridge rectifiers can be classified into single rectifiers and three-phase rectifiers on the basis of the input type they work on. Both these types are further classified into many types based on the type of switching devices used by the rectifier and the types of half-controlled uncontrolled and full-controlled rectifiers. 

In electronic devices, the rectifier used most commonly is the bridge rectifier. 

Working of a Bridge Rectifier Circuit

From the circuit diagrams, it is clear that the diodes are linked in a certain fashion. The name of the converter is based on this unique arrangement. The input voltage in a bridge rectifier can be from any source, such as a transformer used to step up or step down the voltage or from the main domestic electric current supply.

In the half cycle of the first phase of working of the rectifier circuit that is positive, diodes D3-D2 get biased in the forward direction and conduct the current. The diodes D1-D4 get reverse biased and do not conduct the current in this cycle. Therefore, they act as open switches. We obtain a positive half cycle at the output. 

Same way, the diodes D1-D4 are biased in the forward direction in the negative half cycle and conduct the current, while diodes D3-D2 are biased in the reverse direction and therefore do not carry out conduction of the current in this half cycle. Again, a positive half cycle is obtained at the output. When the rectification process is over, there is a conversion of the negative cycle of the AC into a positive cycle. Two half-positive pulses are the output from the rectifier. They have the same magnitude and frequency as that of the input.

Compared to how the half-wave rectifier works, a full bridge rectifier circuit consists of another branch allowing it to conduct during the negative half of the waveform of voltage which the half-bridge rectifier can not do. Therefore, at the output of the full bridge rectifier, the average voltage is double that at the half-bridge rectifier.

Although four separate power diodes are used to produce a full wave bridge rectifier, already-prepared components for the bridge rectifiers are available in different current and voltage sizes that can be directly utilized to make a functioning circuit.

The waveform of the output voltage post-rectification is not a proper direct current. So, it can be converted into a more DC waveform with the help of a capacitor for filtering purposes. Reservoir or smoothing capacitors that are linked in parallel to the load across the full wave bridge rectifier output raises the level of the average DC output to the required average DC voltage at the output. This is due to the fact that the capacitor does not only act as a filtering component but also periodically charges and discharges, increasing the output voltage effectively.

The capacitor keeps on charging until the waveform reaches its peak and uniformly discharges into the load circuit when the waveform starts to decrease. Therefore, when the output is decreasing, the proper voltage supply is maintained by the capacitor into the load circuit, giving rise to direct current.

Advantages of a Bridge Rectifier

The advantages of a bridge rectifier include:

• The output DC signal has lower ripples
• The rectifier is highly efficient
• The power loss is lower

Disadvantages of a Bridge Rectifier

• A bridge rectifier is more complicated as compared to a half-wave rectifier.
• There is more power loss as compared to a center-tapped full wave rectifier.

Center-Tap Rectifier

A center-tap rectifier employs two diodes and a center-cap transformer. 

The transformer of the center-cap rectifier is a dual-voltage transformer having two inputs and three terminals. The two inputs are I1 and I2, while the three terminals are T1, T2, and T3. The terminal T2 is linked to the output coil’s center, which functions as a reference ground. The terminal T1 creates a positive voltage, while the terminal T3 creates a negative voltage concerning the T2. 

Below is the design of a center-tap rectifier:

Positive Half Cycle:

The T1 produces positive, and T2 produces negative voltage during the input positive half cycle. Diode D2 becomes reverse bias while the diode D1 becomes forward biased, making a close path from T1 to T2 via LR or load resistor given below:

Negative Half Cycle:

T1 generates a negative cycle while T2 generates a positive cycle during the input negative half cycle. This puts the diode D2 in forwarding bias while the diode D1 is placed in reverse bias. However, the polarity through RL, the resistor of the load remains unchanged as the current follows a path from T3 to T1 as indicated by the figure below:

The DC output of this type of rectifier is not smooth and steady; rather, it has ripples. These ripples are eliminated by a capacitor at the output and change into a steady DC output.

Applications of Rectifiers

• Rectifiers are employed in electric welding to produce polarized voltage.
• Half-wave rectifiers are used in mosquito repellent devices. They are also used in AM radio as a signal peak detector.
• Rectifiers are utilized in modulation, voltage multipliers, and demodulation.

Conclusion

DC voltage is used for the operation of many electronic circuits. AC voltage or current can be easily converted into DC voltage or current with the help of a device called the p-n junction diode. This device allows the electric current to flow in the forward bias condition while blocking the current in the reverse bias condition. In simple terms, a diode allows the electric current to flow in a single direction. This unique property allows the diode to function as a rectifier. 

Frequently Asked Questions (FAQs)

1.What is a rectifier of half-wave type?

A half-wave rectifier circuit is the type of rectifier that converts only half cycles of the alternating current into direct current.

2.What is Rectification?

It is the process by which an alternating current that changes its direction periodically is converted into a direct current that flows in a single direction.

3.What is a diode?

A diode is a device that allows a unidirectional flow of current. Its working is uncontrolled as it conducts current as well as forward biased.

4.What are the half-wave rectifiers of positive and negative types?

A positive half wave rectifier is the type that changes the positive half cycle of the AC only while blocking the half cycle that is negative.