Half Wave Rectifier Circuit: Working Principle And Characteristics

A rectifier is an electronic device that converts AC voltage into DC voltage. In other words, it converts alternating current to direct current. A rectifier is used in almost all the electronic devices. Mostly it is used to convert the main voltage into DC voltage in the power supply section. By using DC voltage supply electronic devices work. According to the period of conduction, rectifiers are classified into two categories: Half Wave Rectifier and Full Wave Rectifier

Working of Half Wave Rectifier

During the positive half cycle the diode is under forward bias condition and it conducts current to RL (Load resistance). A voltage is developed across the load, which is same as the input AC signal of the positive half cycle.

Alternatively, during the negative half cycle the diode is under reverse bias condition and there is no current flow through the diode. Only the AC input voltage appears across the load and it is the net result which is possible during the positive half cycle. The output voltage pulsates the DC voltage.

Rectifier Circuits

Single-phase circuits or multi-phase circuit comes under the rectifier circuits. For domestic applications single-phase low power rectifier circuits are used and industrial HVDC applications require three-phase rectification. The most important application of a PN junction diode is rectification and it is the process of converting AC to DC.

Single –Phase Rectifiers

Half-Wave Rectification

In a single-phase half-wave rectifier, either negative or positive half of the AC voltage flows, while the other half of the AC voltage is blocked. Hence the output receives only one half of the AC wave. A single diode is required for a single-phase half-wave rectification and three diodes for a three-phase supply. Half wave rectifier produces more amount of ripple content than full wave rectifiers and to eliminate the harmonics it requires much more filtering.

For a sinusoidal input voltage, the no-load output DC voltage for an ideal half wave rectifier is

Vrms = Vpeak / 2

Vdc = Vpeak /

Where

• Vdc, Vav – DC output voltage or average output voltage
• Vpeak – peak value of input phase voltage
• Vrms – the output voltage of root mean square value

Operation of Half-Wave Rectifier

PN junction diode conducts only during the forward bias condition. Half wave rectifier uses the same principle as PN junction diode and thus converts AC to DC. In a half-wave rectifier circuit, a load resistance is connected in series with the PN junction diode. Alternating current is the input of the half wave rectifier. A step down transformer takes input voltage and the resulting output of the transformer is given to the load resistor and to the diode.

During the positive half cycle, the diode is under forward bias condition. During the negative half cycle, the diode is under reverse bias condition. The voltage output is measured across the load resistance. During the positive half cycles the output is positive and significant. And during the negative half cycle the output is zero or insignificant. This is known as half wave rectification.

Working of a Half-Wave Rectifier

During the positive half cycle, when the secondary winding of the upper end is positive with respect to the lower end, the diode is under forward bias condition and it conducts current. During the positive half cycles, the input voltage is applied directly to the load resistance when the forward resistance of the diode is assumed to be zero. The wave forms of output voltage and output current are same as that of the AC input voltage.

During the negative half cycle, when the secondary winding of the lower end is positive with respect to the upper end, the diode is under reverse bias condition and it does not conduct current. During the negative half cycle, the voltage and current across the load remains zero. The magnitude of the reverse current is very small and it is neglected. So, no power is delivered during the negative half cycle.

A series of positive half cycles is the output voltage that is developed across the load resistance. The output is a pulsating DC wave and to make the smooth output wave filters, which should be across the load, are used. If the input wave is of half cycle, then it is known as a half wave rectifier.

Three Phase Half wave Rectifier Circuits

Three phase half wave uncontrolled rectifier requires three diodes, each connected to a phase. Three phase rectifier circuit suffers with high amount of harmonic distortion on both DC and AC connections. There are three distinct pulses per cycle on DC side output voltage.

Half wave Rectifier Characteristics

The characteristics of a half wave rectifier for the following parameters

PIV (Peak Inverse Voltage)

During reverse biased condition, the diode has to withstand because of its maximum voltage. During negative half cycle, no current flows through the load. So, an entire voltage appears across the diode because there is no-voltage drop through load resistance.

PIV of a half wave rectifier = VSMAX

Average and Peak Currents in the Diode

Assuming, the voltage across the secondary of the transformer be sinusoidal and its peak value is VSMAX. Instantaneous voltage which is given to the half wave rectifier is

Vs = VSMAXSin wt

The current flowing through the load resistance is

IMAX = VSMAX / (RF+RL)

Regulation

Regulation is the difference between no-load voltage to full-load voltage with respect to the full-load voltage, and the percentage voltage regulation is given as

Efficiency

The ratio of input AC to output DC is known as efficiency (?).

?= Pdc / Pac

A DC power that is delivered to the load is

Pdc = I2dc RL = (IMAX/ᴨ)2 RL

The input AC power to the transformer,

Pac=Power dissipation in load resistance + power dissipation in the junction diode

= I2rmsRF + I2rmsRL = {I2MAX/4} [RF + RL]

?= Pdc/Pac = 0.406/{1+RF/RL}

The efficiency of a half wave rectifier is 40.6% when RF is neglected.

Ripple Factor (γ)

Ripple content is defined as the amount of AC content present in the output DC. If the ripple factor is less, the rectifier performance will be more. The ripple factor value is 1.21 for a half wave rectifier.

I2 = I2dc + I21 + I22+ I24 = I2dc+ I2ac

γ = Iac / Idc = (I2 – I2dc) / Idc = {( Irms / I2dc) / Idc = {(Irms /I2dc)-1} = kf2-1)

Where kf – form factor

kf= Irms / Iavg = (Imax/2)/ (Imax/ᴨ) =ᴨ/2 = 1.57

So, γ = (1.572 – 1) = 1.21

Transformer Utilization Factor (TUF)

It is defined as the ratio of AC power delivered to the load and transformer secondary AC rating. The TUF of half wave rectifier is about 0.287.

Advantages of Half wave Rectifier

• Cheap
• Simple
• Easy to use
• Low number of components

Disadvantages of Half wave Rectifier

• More amount of ripple content
• Transformer utilization factor is very low
• Rectification efficiency is low
• Generates harmonics

This is all about Half Wave rectifier circuit and working with its characteristics. We believe that the information given in this article is helpful for you for better understanding of this project. Furthermore, for any queries regarding this article or any help in implementing electrical and electronics projects, you can feel free to approach us by commenting in the comment section below. Here is a question for you, what is the main function of half wave rectifier?

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