Full wave Bridge Rectifier
Before going to bridge rectifier, we need to know what actually a rectifier is and what is the need for a rectifier. So first let’s take a look at the evolution of rectifiers.
Evolution of rectifiers
Rectifiers are mainly classified into three types: Half-wave rectifier, Center tapped full-wave rectifier and Bridge rectifier. All these three rectifiers have a common aim that is to convert Alternating Current (AC) into Direct Current (DC).
Not all these three rectifiers efficiently convert the Alternating Current (AC) into Direct Current (DC), only the center tapped full-wave rectifier and bridge rectifier efficiently convert the Alternating Current (AC) into Direct Current (DC).
In half wave rectifier, only 1 half cycle is allowed and the remaining half cycle is blocked. As a result, nearly half of the applied power is wasted in half wave rectifier. In addition to this, the output current or voltage produced by half wave rectifier is not a pure DC but a pulsating DC which is not much useful.
In order to overcome this problem, scientists developed a new type of rectifier known as center tapped full wave rectifier.
The main advantage of center tapped full wave rectifier is that it allows electric current during both positive and negative half cycles of the input AC signal. As a result, the DC output of the center tapped full wave rectifier is double of that of a half-wave rectifier. In addition to this, the DC output of center tapped full wave rectifier contains very fewer ripples. As a result, the DC output of the center tapped full wave rectifier is smoother than the half wave rectifier.
However, the center tapped full wave rectifier has one drawback that is the center-tapped transformer used in it is very expensive and occupies large space.
To cut this extra cost, scientists developed a new type of rectifier known as a bridge rectifier. In bridge rectifier, center tap is not required. If stepping down or stepping up of voltage is not required, then even the transformer can be eliminated in the bridge rectifier.
The rectifier efficiency of a bridge rectifier is almost equal to the center tapped full wave rectifier. The only advantage of bridge rectifier over center tapped full wave rectifier is the reduction in cost.
In bridge rectifier, instead of using the center-tapped transformer, four diodes are used.
Now we get an idea about the three types of rectifiers. The half wave rectifier and the center tapped full wave rectifier (full wave rectifier) are already discussed in the previous tutorials. This tutorial is mainly focused on the bridge rectifier.
Let’s take a look at the bridge rectifier …!
Bridge rectifier definition
A bridge rectifier is a type of full wave rectifier which uses four or more diodes in a bridge circuit configuration to efficiently convert the Alternating Current (AC) into Direct Current (DC).
Bridge rectifier construction
The construction diagram of a bridge rectifier is shown in the below figure. The bridge rectifier is made up of four diodes namely D1, D2, D3, D4 and load resistor RL. The four diodes are connected in a closed loop (Bridge) configuration to efficiently convert the Alternating Current (AC) into Direct Current (DC). The main advantage of this bridge circuit configuration is that we do not require an expensive center tapped transformer, thereby reducing its cost and size.
The input AC signal is applied across two terminals A and B and the output DC signal is obtained across the load resistor RL which is connected between the terminals C and D.
The four diodes D1, D2, D3, D4 are arranged in series with only two diodes allowing electric current during each half cycle. For example, diodes D1 and D3 are considered as one pair which allows electric current during the positive half cycle whereas diodes D2 and D4 are considered as another pair which allows electric current during the negative half cycle of the input AC signal.
How bridge rectifier works?
When input AC signal is applied across the bridge rectifier, during the positive half cycle diodes D1 and D3 are forward biased and allows electric current while the diodes D2 and D4 are reverse biased and blocks electric current. On the other hand, during the negative half cycle diodes D2 and D4 are forward biased and allows electric current while diodes D1 and D3 are reverse biased and blocks electric current.
During the positive half cycle, the terminal A becomes positive while the terminal B becomes negative. This causes the diodes D1 and D3 forward biased and at the same time, it causes the diodes D2 and D4 reverse biased.
The current flow direction during the positive half cycle is shown in the figure A (I.e. A to D to C to B).
During the negative half cycle, the terminal B becomes positive while the terminal A becomes negative. This causes the diodes D2 and D4 forward biased and at the same time, it causes the diodes D1 and D3 reverse biased.
The current flow direction during negative half cycle is shown in the figure B (I.e. B to D to C to A).
From the above two figures (A and B), we can observe that the direction of current flow across load resistor RL is same during the positive half cycle and negative half cycle. Therefore, the polarity of the output DC signal is same for both positive and negative half cycles. The output DC signal polarity may be either completely positive or negative. In our case, it is completely positive. If the direction of diodes is reversed then we get a complete negative DC voltage.
Thus, a bridge rectifier allows electric current during both positive and negative half cycles of the input AC signal.
The output waveforms of the bridge rectifier is shown in the below figure.
Characteristics of bridge rectifier
Peak Inverse Voltage (PIV)
The maximum voltage a diode can withstand in the reverse bias condition is called Peak Inverse Voltage (PIV)
or
The maximum voltage that the non-conducting diode can withstand is called Peak Inverse Voltage (PIV).
During the positive half cycle, the diodes D1 and D3 are in the conducting state while the diodes D2 and D4 are in the non-conducting state. On the other hand, during the negative half cycle, the diodes D2 and D4 are in the conducting state while the diodes D1 and D3 are in the non-conducting state.
The Peak Inverse Voltage (PIV) for a bridge rectifier is given by
PIV = VSmax
Ripple factor
The smoothness of the output DC signal is measured by using a factor known as ripple factor. The output DC signal with very fewer ripples is considered as the smooth DC signal while the output DC signal with high ripples is considered as the high pulsating DC signal.
Ripple factor is mathematically defined as the ratio of ripple voltage to the pure DC voltage.
The ripple factor for a bridge rectifier is given by
The ripple factor of the bridge rectifier is 0.48 which is same as the center tapped full wave rectifier.
Rectifier efficiency
The rectifier efficiency determines how efficiently the rectifier converts Alternating Current (AC) into Direct Current (DC).
High rectifier efficiency indicates a most reliable rectifier while the low rectifier efficiency indicates a poor rectifier.
Rectifier efficiency is defined as the ratio of the DC output power to the AC input power.
The maximum rectifier efficiency of a bridge rectifier is 81.2% which is same as the center tapped full wave rectifier.
Advantages of bridge rectifier
Low ripples in the output DC signal
The DC output signal of the bridge rectifier is smoother than the half wave rectifier. In other words, the bridge rectifier has fewer ripples as compared to the half wave rectifier. However, the ripple factor of the bridge rectifier is same as the center tapped full wave rectifier.
High rectifier efficiency
The rectifier efficiency of the bridge rectifier is very high as compared to the half wave rectifier. However, the rectifier efficiency of bridge rectifier and center tapped full wave rectifier is same.
Low power loss
In half wave rectifier only one half cycle of the input AC signal is allowed and the remaining half cycle of the input AC signal is blocked. As a result, nearly half of the applied input power is wasted.
However, in the bridge rectifier, the electric current is allowed during both positive and negative half cycles of the input AC signal. So the output DC power is almost equal to the input AC power.
Disadvantages of bridge rectifier
Bridge rectifier circuit looks very complex
In a half wave rectifier, only a single diode is used whereas in a center tapped full wave rectifier two diodes are used. But in the bridge rectifier, we use four diodes for the circuit operation. So the bridge rectifier circuit looks more complex than the half wave rectifier and center tapped full wave rectifier.
More power loss as compared to the Center tapped full wave rectifier
In electronic circuits, the more diodes we use the more voltage drop will occur. The power loss in bridge rectifier is almost equal to the center tapped full wave rectifier. However, in a bridge rectifier, the voltage drop is slightly high as compared to the center tapped full wave rectifier. This is due to two additional diodes (total four diodes).
In center tapped full wave rectifier, only one diode conducts during each half cycle. So the voltage drop in the circuit is 0.7 volts. But in the bridge rectifier, two diodes which are connected in series conduct during each half cycle. So the voltage drop occurs due to two diodes which is equal to 1.4 volts (0.7 + 0.7 = 1.4 volts). However, the power loss due to this voltage drop is very small. bridge refctifier with filter
Bridge rectifier with filter
In center tapped full wave rectifier, both positive and negative half cycles are rectified. So no voltage is wasted at the output. Furthermore, the DC output produced by center tapped full wave rectifier is smoother than the half wave rectifier output.
However, the center tapped full wave rectifier has one drawback. That is the transformer used in the center tapped full wave rectifier is very costly and it occupies large space. So to overcome this drawback, a new type of rectifier was developed called bridge rectifier.
In bridge rectifier, the transformer is not needed. However, two extra diodes (total four diodes) are needed to operate the bridge rectifier.
The overall cost of the bridge rectifier is low as compared to the center tapped full wave rectifier.
Like the center tapped full wave rectifier, the output Direct Current (DC) of the bridge rectifier contains small ripples. These small ripples can be reduced if we use the filter at the output.
The filter converts the pulsating Direct Current (DC) into pure Direct Current (DC). The filter is made up of a combination of components such as capacitors, resistors, and inductors.
In this tutorial, a bridge rectifier made up of capacitor filter is explained.
Like the center tapped full wave rectifier, the bridge rectifier also rectifies both positive and negative half cycles of the input AC signal. However, the construction of bridge rectifier is different from the center tapped full wave rectifier. In bridge rectifier, the diodes are arranged in the bridge circuit configuration.
The bridge rectifier is made up of four diodes namely D1, D2, D3 and D4. The input signal is applied across the two terminals A and B while the DC output is obtained across the load resistor RL connected between the terminals C and D.
The pulsating DC output obtained across the load resistor RL contains small ripples. To reduce these ripples, we use a filter at the output.
The filter normally used in the bridge rectifier is a capacitor filter. In the below circuit diagram, the capacitor filter is connected across the load resistor RL..
When input AC signal is applied, during the positive half cycle both diodes D1 and D3 are forward biased. At the same time, diodes D2 and D4 are reverse biased.
On the other hand, during the negative half cycle, diodes D2 and D4 are forward biased. At the same time, diodes D1 and D3 are reverse biased.
Thus, the bridge rectifier allows both positive and negative half cycles of the input AC signal.
The DC output produced by the bridge rectifier is not a pure DC but a pulsating DC. This pulsating DC contains both AC and DC components.
The AC components fluctuate with respect to time while the DC components remain constant with respect to time. So the AC components present in the pulsating DC is an unwanted signal.
The capacitor filter present at the output removes the unwanted AC components. Thus, a pure DC is obtained at the load resistor RL.
