Rectfier: Understanding Rectifiers

Rectifiers Feature
Rectifiers Feature

1. What is a Rectifier ?

Rectifier in electronics engineering forms a basic building block for any type of circuit.It is a electrical component which converts Alternating Current (AC) to pulsating Direct Current (DC). It is a semiconductor device ie. rectifier uses diode for its operation. Most electronics circuit operate on D.C (Direct Current). But generation and transmission of A.C power is far easy and economical. So to convert the A.C power into D.C we use a rectifier circuit.

2. Need of Rectifier ?

As mentioned earlier, almost all the electronic devices such as diodes, transistors, IC’s, electronic circuits require DC voltage to operate linearly and for proper operation. DC voltage is supplied through dry cells and batteries. But these sources of voltage are not economical for continuous use. The electronic device called rectifier has the property to convert  alternating current (AC) to direct current (DC). So, rectifiers can be used as substitute for source, therefore, there is a need of rectifier to supply DC voltage which is required in electronic circuits.

3.Types of Rectifiers?

Depending upon operation and the power delivered to the load rectifier is classified into three types:

  1. Half Wave Rectifiers
  2. Full Wave Rectifiers
  3. Full Wave Bridge Rectifiers (Most Commonly Used)

(a) Half Wave Rectifier:

half wave rectifier
half wave rectifiers

A Half Wave Rectifier is similar like a single PN junction diode connected in series to the load resistor. As we know that a PN junction diode conducts only in ON direction i.e. Forward Bias. The same principle is used in half wave rectifier to convert AC to pulsating DC.The Half Wave Rectifiers consists of a single diode. The input we give is AC this input voltage is stepped down using a transformer.The reduced voltage is fed to the diode ‘D’ and load resistance RL. During the positive half cycles of the input wave, the diode ‘D’ will be forward biased and during the negative half cycles of input wave, the diode ‘D’ will be reverse biased. We take the output across load resistor RL. Since the diode passes current  only during one half cycle of the input wave, we get an positive output . The output is positive and significant during the positive half cycles of input wave. At the same time output is zero or insignificant during negative half cycles of input wave. The maximum rectification efficiency is 40.06%  This is called Half Wave Rectification.

(b) Full Wave Rectifier:

full wave rectifier
full wave rectifiers

A Full Wave Rectifier is a circuit, which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage. It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied.

Types:

(i) FULL WAVE BRIDGE RECTIFIERS

(ii) CENTRE-TAP FULL WAVE RECTIFIERS

 CONCEPT OF A FULL WAVE BRIDGE RECTIFIERS:

A rectifiers using a diode bridge that allows the unidirectional (DC) current to flow through the load during the entire period of input AC cycle is called a bridge rectifiers.

CONCEPT OF A CENTRE-TAP FULL WAVE RECTIFIER:

In a half wave rectifiers, only one half cycle we use, whereas, in a full wave rectifiers both half-cycles of input AC signal are used. A full wave rectifier is an electronic circuit which allows the unidirectional current to flow through the load during the entire period of the input AC cycle.

(4) WHY ALWAYS BRIDGE RECTIFIERS ?

full wave bridge rectifier
full wave bridge rectifier

As we know the bridge rectifiers is the most widely used full-wave rectifiers because it does not require centre-tape secondary winding transformer. We can also get rectification without the use of transformer, only if the stepping up or stepping down of voltage is not required. When higher output DC voltages are required, the Peak Inverse Voltage (PIV) of each diode must be equal to the peak secondary voltage (Vm). The Transformer Utilization Factor (TUF) is very high which leads to maximum conversion of AC power to DC power.

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