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What Is Rectifier? Types Of Rectifiers

What Is Rectifier? Different Types Of Rectifiers (Controlled & Uncontrolled Rectifiers)

In Electronics, Rectifier circuit is the most used circuit because almost every electronic appliance operates on DC (Direct Current) but the availability of the DC Sources are limited such as electrical outlets in our homes provide AC (Alternating current). The rectifier is the perfect candidate for this job in industries & Home to convert AC into DC. Even our cell phone chargers use rectifiers to convert the AC from our home outlets to DC. Different types of Rectifiers are used for specific applications.

Usually, the types of Rectifiers are classified based on their output. In this article, we will discuss different types of Rectifiers.

What Is Rectifier Different Types Of Rectifiers

 

Rectifier

A Rectifier is an electrical device that is made of one or more than one diodes that converts the alternating current (AC) into direct current (DC).

Rectification

Rectification is the process of conversion of the alternating current (which periodically changes direction) into direct current (flow in a single direction).

Types Of Rectifiers

There are mainly two types of rectifiers:

  1. Uncontrolled Rectifier
  2. Controlled Rectifier

Uncontrolled Rectifier:

The type of rectifier whose output voltage cannot be controlled is called an uncontrolled rectifier.

Uncontrolled rectifier uses only diodes and they give a fixed output voltage depending only on the AC input.

Types Of Uncontrolled Rectifier:

Uncontrolled Rectifiers are further divided into two types:

  1. Half Wave Rectifier
  2. Full Wave Rectifier
Half Wave Rectifier:

A Type of rectifier that converts only the half cycle of the alternating current (AC) into direct current (DC) is known as halfwave rectifier.

  • Positive half wave rectifier:

A half wave rectifier that converts only the positive half cycle and blocks the negative half cycle.

Positive & Negative Half Wave Rectifier

  • Negative halfwave rectifier:

A negative half wave rectifier converts only the negative half cycle of the AC into DC.

In all types of rectifiers, a half-wave rectifier is the simplest of them all as it is composed of only a single diode.

Half wave rectifier

A diode allows the current flow in only one direction known as forward biasA load resistor RL is connected in series with the diode.

Positive Half Cycle:

During the positive half cycle, the diode terminal anode will become positive and the cathode will become negative known as forward bias. And it will allow the positive cycle to flow through.

Half Wave During Postive Half Cycle

Negative Half Cycle:

During the negative half cycle, the anode will become negative and the cathode will become positive, which is known as reverse bias. So the diode will block the negative cycle.

Half Wave During Negative Half Cycle

So when an AC source is connected to the half-wave rectifier, only half cycle will flow through it as shown in the figure below.

Half Wave Rectifier Output

The output of this rectifier is taken across the load resistor RL. if we look at the input-to-output graph, it shows a pulsating positive half cycle of the input.

The output of the half wave rectifier has too many ripples & it is not very practical to use this output as DC source. To smooth this pulsating output, a capacitor is introduced across the resistor. The capacitor will charge during the positive cycle and discharge during the negative cycle to give out a smooth output signal.

Half Wave Rectifier Output with Capacitor

Also read: How To Test A Diode & Methods Of Diode, LED & Zener Diode Test

 

Such types of rectifiers waste the power of AC input’s half cycle.  

Full Wave Rectifier:

A full wave rectifier converts both positive and negative half cycles of the AC (alternating current) into DC (direct current). It provides double output voltage compared to the halfwave rectifier

A full wave rectifier is made up of more than one diode.

There are two types of full wave rectifier.

  1. Bridge Rectifier
  2. Center-Tap Rectifier
Bridge Rectifier

A bridge rectifier uses four diodes to convert both half cycle of the input AC  into DC output.

In this type of rectifier, the diodes are connected in a specific form as given below.

Bridge Rectifier

Positive Half Cycle:

During input positive half cycle, the diode D1 & D2 becomes forward bias while D3 & D4 becomes reverse bias. The diode D1 & D2 form a closed loop that provides a positive output voltage across the load resistor RL.

Bridge Rectifier During Positive Cycle

Negative Half Cycle:

During the negative half cycle, the diode D3 & D4 becomes forward bias while D1 & D2 becomes reverse bias. But the polarity across the load resistor RL remains the same and provides a positive output across the load.

Bridge Rectifier During Negative Cycle

The output of full wave rectifier has low ripples compared to half-wave rectifier but still, it’s not smooth and steady.

Bridge Rectifier Output

In order to make the output voltage smooth & steady, a capacitor is placed at the output as shown in the figure below.

Bridge Rectifier Output With Capacitor

The capacitor charge & discharges which make smooth transitions between the half cycles.

Center-Tap Rectifier

This type of full-wave rectifier uses a center-tap transformer & two diodes.

Center Tap Transformer

A center-tap transformer is a dual-voltage transformer that has two inputs (I1 & I2) and three output terminals (T1, T2, T3). The T2 terminal is connected to the center of the output coil which acts as a reference ground (o volt reference). The T1 terminal produces positive voltage and the T3 terminal produces negative voltage with respect to the T2.

The design of the center-tap rectifier is given below:

Center Tap Rectifier

Postive Half Cycle:

During the input positive half cycle, the T1 will produce positive and T2 will produce a negative voltage. The diode D1 will become forward bias & diode D2 will become reverse bias. This makes a close path from T1 to T2 through the load resistor RL as shown below.

Center Tap Rectifier During Positive Cycle

Negative Half Cycle:

Now during the input negative half cycle, T1 will generate negative cycle & T2 will generate a positive cycle. This will put the diode D1 into reverse bias & diode D2 in forward bias. But the polarity across the load resistor RL is still the same as the current takes the path from T3 to T1 as shown in the figure below.

Center Tap Rectifier With Capacitor

Also read: Introduction To Transformer & Its Working Principle, Design Aspects & Safety Precautions

 

The DC output of a center-tap rectifier also has ripples and it’s not smooth & steady DC. A capacitor at the output will remove the ripple and make a steady DC output.

Controlled Rectifier:

A type of rectifier whose output voltage can be varied or changed is called controlled rectifier.

It is composed of one or more than one SCR (Silicon Controlled Rectifier).

An SCR, also known as thyristor is a three-terminal diode. These terminals are Anode, Cathode & a control input known as Gate.

Just like a simple diode an SCR conduct in forward bias and blocks current in reverse bias but it only starts forward conduction when there is a pulse at the gate input. So the output voltage can be controlled using the gate input.

Types of controlled rectifier

There are two types of controlled rectifier.

Half Wave Controlled Rectifier

The half wave controlled rectifier is made up of a single SCR (Silicon Controlled Rectifier).

Half wave controlled rectifier has the same design as the half wave uncontrolled rectifier except we replace the diode with an SCR as shown in figure down below.

Half Wave Controlled Rectifier

An SCR does not conduct in reverse bias, so it will block the negative half cycle.

During the positive half cycle, the SCR will conduct current on one condition when a pulse is applied to the gate input. The gate input is, of course, a periodic pulse signal which is designed to activate the SCR at each positive half cycle.

In this way, we can control the output voltage of this rectifier.

The output of the SCR is also a pulsating DC voltage/current. These pulses are removed by using a capacitor parallel to the load resistor RL.

Half Wave Controlled Rectifier With Capacitor

Full Wave Controlled Rectifier

A type of rectifier that converts both positive and negative half cycle of the AC into DC as well as controls the output amplitude is known as a full wave controlled rectifier.

Just like uncontrolled rectifier, controlled full wave rectifier has two types.

Controlled Bridge Rectifier

In this rectifier, the diode bridge is replaced by an SCR (Thyristor) bridge with the same configuration as shown in the figure below.

Controlled Bridge Rectifier

Also Read: Basic Electronics Engineering Interview Questions

 

Positive Half Cycle:

During the positive cycle, the SCR (thyristor) T1 & T2 will conduct when the gate pulse is applied. T3 & T4 will be reversed bias, so they will block the current. The output voltage will be established across the load resistor RL as shown below.

Controlled Bridge Rectifier During Positive Cycle

Negative Half Cycle:

During the negative half cycle, the thyristor T3 & T4 will become forward bias considering the gate input pulse & the T1 & T2 will become reverse bias. The output voltage will appear across the load resistor RL.

Controlled Bridge Rectifier During Negative Cycle

At the end of the output, a capacitor is used to remove the ripples and makes the output steady & smooth.

Controlled Bridge Rectifier With Capacitor

Controlled Center-Tap Rectifier:

Just like center-tap uncontrolled rectifier, this design uses two SCR replacing the two diodes.

Both of these SCR switchings will be timed differently according to the input AC frequency.

Its operation is the same as the uncontrolled rectifier & its schematic design is given below.

Controlled Center Tap Rectifier With Capacitor

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