What exactly are Rectifiers?
A rectifier is an electrical device made up of one or more diodes that allow current to flow only in one direction. It essentially changes alternating current to direct current.
Rectifiers can be molded into a variety of shapes depending on the application, such as semiconductor diodes, SCRs (silicon controlled rectifiers), vacuum tube diodes, mercury-arc valves, and so on. In this article, we will go over rectifiers in detail.
Classification of Rectifiers
Rectifiers are classified into various designs based on factors such as power supply type, bridge configuration, components used, control nature, and so on.
These are primarily divided into two types: single-phase and three-phase rectifiers. Rectifiers are further classified into three types:
- Uncontrolled Rectifiers
- Half-controlled Rectifiers, and
- Fully controlled rectifiers
Let us look at some of these rectifiers in more detail.
A controlled rectifier is a circuit that converts an alternating current supply into a unidirectional direct current supply and can control the power fed to the load. Controlled Rectification refers to the process of converting A.C to D.C.
Types of Controlled Rectifiers
Controlled rectifiers are classified into two types:
- Half wave Controlled Rectifiers and
- Full wave Controlled Rectifiers.
Half Wave Controlled Rectifiers
As the name implies, a Half Wave Controlled Rectifier is a rectifier circuit that converts AC input into DC output only during the positive half cycle of the AC input supply.
A rectifier operates with switches, which come in both controllable and uncontrollable varieties.
An uncontrolled rectifier is a type of rectifier whose voltage cannot be controlled.
A two-terminal component, such as a diode, is a unidirectional device whose primary function is to allow current to flow in only one direction. This device cannot be controlled because it will only function when connected in forward bias.
When a diode is connected to a rectifier in any configuration, the rectifier cannot be completely controlled by an operator and is referred to as an uncontrolled rectifier.
It does not allow the power to change based on the load requirements. As a result, this type of rectifier is typically found in fixed or stable power supplies. This type of rectifier only uses diodes and provides a stable output voltage based on an alternating current input.
Uncontrolled rectifiers are classified further as follows:
- Half Wave Uncontrolled Rectifiers
- Full Wave Uncontrolled Rectifiers
Half Wave Uncontrolled Rectifiers
A halfwave rectifier is a type of rectifier that allows only one-half of an alternating current voltage waveform to pass while blocking the other half.
When an alternating current supply is applied to the input of this type of rectifier, only the positive half cycle is visible across the load, while the negative half cycle is obscured.
A single diode is required in a single-phase supply, while three diodes are required in a three-phase supply.
Types of Half-wave Rectifiers
Positive Half Wave Rectifiers
A positive half wave rectifier is defined as one that simply changes the positive half cycle while blocking the negative half cycle.
Negative Half Wave Rectifiers
A negative half-wave rectifier is one that simply converts the negative half cycle of an alternating current into direct current.
Full Wave Uncontrolled Rectifiers
A full wave rectifier is one that converts the entire cycle of alternating current into pulsating direct current.
When an alternating current supply is applied to the i/p during both half cycles, the current flowing through the load flows in the same direction.
By changing both polarities of the i/p waveform to pulsating DC, this circuit produces a higher standard output voltage.
This type of rectification can be accomplished by using at least two crystal diodes that conduct current in opposite directions.
The center tap full wave rectifier and full-wave bridge rectifier are used to get the same direction of current flow in the load resistor during the positive and negative half-cycles of the input AC.
Types of Full Wave Rectifiers
A full-wave rectifier circuit contains more than one diode. Bridge rectifiers and center tap rectifiers are the two types of full wave rectifiers.
The bridge rectifier is a type of full-wave rectifier that converts alternating (AC) current to direct (DC) current by using four or more diodes in a bridge circuit configuration.
Center Tap Full-wave Rectifiers
A center tapped full wave rectifier is a type of rectifier that converts the entire AC signal into DC using a center tapped transformer and two diodes.