In this chapter, we are going to learn about second type of rectifier that is full wave rectifier. Unlike half wave, full wave rectifier is mostly used.

We have already discussed rectifier and half wave rectifier in our previous tutorials. From them, we got to know that there is a vast difference between the characteristics and efficiency of different rectifiers. Now we will learn the types and characteristics of full wave rectifier.

In this Article You will learn:

## Full Wave Rectifier

Full wave rectifiercan be defined as “a type of rectifier that converts the alternating voltage into pulsating direct voltage but unlike half wave rectifier, it uses both cycles of the input voltage. For this AC to DC conversion, it uses 2 diodes.”This rectifier acts a heart of circuitry which allows the sensors to attach to the RCX in either polarity.

In this rectifier, **full wave rectification** is achieved by using two crystal diodes which conduct current alternatively. During positive as well as the negative half cycle of input AC, the two circuits are employed to obtain the same direction of current flow in the load resistor.

## Full Wave Rectifier Circuits

This rectifier is further classified into 2 types namely: Center Tap Full-wave Rectifier and Full wave Bridge Rectifier. Each of these has its own working operation and features. Now we are going to understand these circuits in detail.

## Center Tap Full-wave Rectifier

This **rectifier** is widely used in the vacuum tubes and thermionic valves. It employs a tapped transformer with secondary winding AB tapped at the center point C, two diodes D_{1 }and D2 are connected in the upper half and the lower half portion of the circuit.

For rectification, the Diode D_{1 }utilizes the AC voltage appearing across the upper half of the secondary winding while D2 uses the lower half of secondary winding.

### Center Tapped Rectifier Working Operation

The circuit diagram of full wave rectifier circuit with waveform is shown in the below figure. The alternating voltage V_{in }appears across the terminals AB of the secondary winding of the** transformer** when AC supply is switched on.

During **positive half cycle** at a given voltage, end A of the transformer become positive while end B become negative which makes the D_{1 }diode forward biased and the D2 diode reverse biased. Due to this reason, the diode D_{1} conducts current while D2 does not conduct current.

As shown in the above figure, the current starts flowing through diode D_{1}, and output voltage V_{out} is measured across load resistor R_{L}. This means current flows only in the upper portion of the secondary winding of the transformer. The path of the current is shown by bold arrows.

During **Negative Half Cycle**, the end B of the transformer becomes positive while the end A becomes negative. This makes the D_{1 }diode reverse biased and the D2 diode forward biased. Due to this reason, now the diode D_{1} does not conduct current while D2 conducts.

As shown in the figure above, the current starts flowing through diode D_{2}, and through load resistor R_{L }in the lower portion of the secondary by dotted arrows.

Note: During Negative as well as positive half-cycle of the input AC voltage, the current flows through the load resistor R

_{L }in the same direction.

Therefore across the **load resistor** R_{L, } DC output voltage V_{out} is obtained.

The waveform diagrams of the current flowing through the load, applied input voltage and output voltage developed across the load are shown in the above figure.

## Full-wave Bridge Rectifier

Bridge Rectifier is another type of full wave rectifier, that uses 4 diodes instead of 2. It also does not require any center tapping. As the name suggests, it is a bridge rectifier, so we can conclude that it uses a bridge circuit.

These 4 individual rectifying diodes are connected in a *closed-loop bridge configuration*. Having no requirement of a special center-tapped transformer makes it smaller in size & cheaper at cost.

### Bridge Rectifier Working Operation

As shown in the figure above, the bridge rectifier has 4 diodes; namely D_{1}, D_{2}, D_{3}, D_{4}. Out of these 4 diodes of the bridge, only two diodes conduct at a time. Either “D_{1} and D_{3}” conducts or “D_{2} and D_{4}” conducts or vice-versa depending upon the positive or negative half cycle fed to the bridge circuit.

Now, let us understand this taking both cases:

**Positive Half Cycle:**

When the positive half cycle is fed to the bridge circuit, Diodes “D_{2} and D_{4}” are positively biased. While Diode “D_{1} and D_{3}” are negatively biased. This means only “D_{2} and D_{4}” will conduct.

The direction of the current is shown in the above figure.

**Negative Half Cycle:**

When the negative half cycle is fed to the bridge circuit, Diodes “D_{1} and D_{3}” are positively biased. While Diode “D_{2} and D_{4}” are negatively biased. This means only “D_{1} and D_{3}” will conduct.

The direction of the current is shown in the above figure.

Here most important point to note is, the direction of current flow is same in both cases. This means, the current is unidirectional and so the voltage-drop is also unidirectional.

You can also watch video on Full Wave Rectifier by Neso Academy

## Full wave Rectifier Characteristics

For the analysis of Full wave rectifier following parameters value or properties are considered. Following of its characteristics are:

### Ripple Factor

Ripple factor is defined as the ratio of the RMS value of the AC component to the DC component. Therefore,

**Ripple factor = RMS value of AC component / value of DC component**

This factor mainly decides the effectiveness of a rectifier i.e. *smaller the value of this factor, lesser is the AC component in comparison to the DC component*. Hence, more effective is the rectifier.

#### Ripple Factor Calculation Equation

The Ripple Factor of Full wave rectifier can be calculated as follows:

As we know,

I_{rms} = √ I_{dc}^{2 }+ I_{ac}^{2}

Where,

I_{rms }= RMS value of total load current

I_{dc }= value of dc component of the load current

I_{ac }= RMS value of the AC component of load current

Therefore,

I_{ac }= √ I_{rms}^{2} – I_{dc}^{2}

As we know,

Ripple factor = I_{ac }/ I_{dc}

_{ }= √ I_{rms}^{2} – I_{dc}^{2} / I_{dc}

= √ (I_{rms }/ I_{dc})^{2} -1

For full wave rectifier, ripple factor is calculated as:

As we know,

**I _{rms }/ I_{dc} = ( I_{m} / √ 2) / (2 I_{m} /π) = 1.11**

Therefore,

**Ripple factor = √ (1.11) ^{2} -1 = 0.482**

### Efficiency Calculation

The** efficiency of rectifier **is defined as the ratio of DC power output to the input AC power. Therefore,

**Efficiency = DC power output / AC power input**

= 0.812 R_{L / }(r_{f }+ R_{L})

If r_{f }is_{ }neglected as compared to RL, the efficiency of the rectifier is maximum given as;

**η _{max} = 0.812 = 81.2%**

Hence the *efficiency of full wave rectifier *is 81.2%. Or we can say that Full wave rectifier is 81.2% efficient.

### Peak Inverse Voltage (PIV)

**Peak inverse voltage** is defined as the maximum value of the voltage coming out of the diode when it is reverse biased during the negative half cycle. For *center tap full wave rectifier* its value is 2V_{m }and for the **bridge rectifier,** its value is V_{m.}

### Transformer Utilization Factor (TUF):

It is defined as the ratio of power delivered to load and VA rating of the transformer. For center tap full wave rectifier its value is 0.573_{ }and for the bridge rectifier**,** its value is 0.812.

## Advantages and Disadvantages

**Advantages:**

Advantages of full wave rectifier are:

- The output and efficiency of center tap full wave rectifier are high because AC supply delivers power during both the halves.
- For the same secondary voltage bridge rectifier has double output.

**Disadvantages:**

Following of disadvantages of full wave rectifier are:

- Full wave rectifier requires more diodes i.e two for center tap rectifier and four for bridge rectifier.
- When a small voltage is required to be rectified the full wave rectifier circuit is not suitable.
- In center tap full wave rectifier, center on the secondary winding for tapping is difficult.

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