Diode Bridge Full Wave Rectifier

Diodes are the most basic and important component in electronics, they are used in a variety of applications. Of those applications, rectifiers are the most popular one.

 

Rectifiers are the circuits or devices that convert AC voltage into DC voltage by employing different types of power semiconductor devices, which have unidirectional current conduction properties, “diodes are the one of those devices“.

 

Majorly, there are two types of rectifier circuit used in modern electronics: half wave rectifiers and full wave rectifiers. Full wave rectifiers use two types of circuit configurations that are bridge rectifier circuit and centre tapped rectifier circuit. Among those rectifiers, bridge rectifiers are the most popular ones.

 

Rectifier circuits that employ diodes are generally called uncontrolled rectifiers, as in diodes, we cannot control their conduction. Unlike controlled rectifiers, we cannot control or regulate the DC output voltage of these rectifiers. These circuits provide fixed DC voltage from a fixed AC input voltage.

 

In this article, we will cover the important concept of bridge rectifiers using diodes including their circuit diagram, working, formulas, advantages, disadvantages and applications.

Diode Bridge Full Wave Rectifier

 

A diode bridge full wave rectifier or diode bridge rectifier is a type of full wave rectifier circuit that converts AC voltage into DC voltage by using diodes, which are connected in a bridge-like arrangement. This type of rectifier circuit provides fixed DC voltage from a fixed AC voltage, and is therefore called an uncontrolled bridge rectifier (as discussed above).

 

 

Diode Bridge Rectifier Circuit Diagram

In diode bridge rectifier circuit four diodes are connected in a bridge-like arrangement, as shown in the given figure. 

In the given figure we see that the voltage source V_s = V_m. sin(ωt) is connected between the two diagonally opposite points a & b of the bridge and the load is connected between the other two diagonally opposite corners c & d of the bridge. For the sake of simplicity, we consider the load is resistive, drawing the current Io from the diode bridge circuit, with the voltage drop across it is Vo.

 

Diode Bridge Rectifier Working 

 

As we know, a diode bridge full wave rectifier circuit converts both halves of AC input supply into DC voltage. For the efficient conversion of both halves of AC input supply, in a diode bridge rectifier circuit, two diagonally opposite diodes conduct for positive half and the other two diagonally opposite diodes conduct for negative half of AC input supply.

 

Let us understand the working diode bridge full wave rectifier step by step. To make it easy to understand we consider the diodes to be ideal. By “ideal" we mean that the reverse time and the forward voltage drop of the diodes are negligible.

 

As we know, the AC voltage waveform is sinusoidal in nature, as shown in the given figure, and can be expressed as V_s =V_m sinωt. The magnitude of this waveform changes continuously with time, it is positive for the 0 to π, called positive half and it is negative for 0 to 2π called negative half. After 2π, this waveform repeats itself, means the fundamental time period of this waveform is 2π.

Where,

V_s        =         Instantaneous Value of the applied voltage waveform

V_m       =         Peak Value of the applied voltage waveform

ω        =        Angular frequency

t          =         time

V_sr      =          RMS Value of the applied voltage waveform

When the positive half of AC supply is applied to the rectifier circuit, then the point a is positive with respect to b. As a result, the diodes D1 & D2 are forward biased and the diodes D3 & D4 are reverse biased. Since the diodes D1 and D2 are forward biased they allow the current conduction, behave like a short circuit, whereas the diodes D3 & D4 being the reverse biased, do not allow the current conduction and act like open circuit. During this period, the direction of the flow of current in the circuit can be visualized with the help of the given figure, and the voltage across the load is similar to the input voltage.

When negative half of AC supply is applied to the circuit then the point b is positive with respect to a hence, the diodes D3 and D4 are forward biased and diodes D1 and D2 are reverse biased. As the diodes D3 and D4 are forward they allow the current conduction, behave like a short circuit and the reverse diodes diodes D1 & D2 do not allow the current conduction, behave like open circuit. During this time the direction of the current flow in the circuit can be visualized with the help of the given figure and the voltage across the load is the negative of the input voltage.

Diode Bridge Rectifier Output Waveform

 

As per the above discussion on the working of diode bridge rectifiers we can conclude that the output voltage waveform of the diode bridge full wave rectifier is shown as the given figure.

Important Formulas of Diode Bridge Rectifier 

 

Output Voltage of Diode Bridge Rectifier 

Average value of the output voltage for the Diode Bridge Rectifier

Vo  =   1/T ₀ʃ^T V_m. sin(ωt).                                             

Vo  =  1/π  ₀ ʃ^π V_m. sin(ωt).

So, the average output current for resistive load is

 

RMS Value of the  voltage for the Diode Bridge Rectifier

Vo _rms      =      (1/T  ₀ʃ^T (V_m. sinwt)² )^1/2

Vo _rms      =      (1/π  ₀ ʃ^π  (V_m. sinwt)² )^1/2

Advantages of Diode Bridge Rectifier

• There are certain advantages of using diode bridge full wave rectifier over other rectifier circuits these are

• Diode bridge full-wave rectifiers are more efficient compared to half-wave rectifiers because they utilize both halves of the AC input waveform. 

• Diode Bridge full wave rectifiers are economically cheaper as compared to other full wave rectifier circuits such as controlled rectifier and half controlled rectifier because these circuits use controlled switches such as SCR, MOSFET etc., which are a bit expensive. 

• A diode bridge rectifier circuit is preferably used over center tap rectifier circuit because center tap rectifier requires a center tap transformer which makes this circuit bulkier and costlier. And diodes used in center tap rectifier circuits have high peak inverse voltage and high PIV diodes are costlier.

Applications of Diode Bridge Rectifier

It is important to note that diode bridge full wave rectifiers are uncontrolled rectifiers, means they lack the ability to control or regulate the DC output voltage. Despite this drawback diode bridge full wave rectifiers are most widely used in those applications of modern electronics where control of DC output voltage is not necessary like in battery chargers for mobile, laptop, or any other electronics equipment, in TVs, LED driver circuits etc.