- Bridge Rectifier Definition: A bridge rectifier is a circuit that converts AC to DC using four diodes arranged in a bridge configuration.
- Working Principle: It works by allowing current to flow through different pairs of diodes based on the input polarity, ensuring the output polarity remains the same.
- Circuit Diagram: The diagram includes four diodes connected to an AC input and a load resistor, showing how current flows in each cycle.
- Pulsating DC Output: The output is pulsating DC, which can be smoothed using a capacitor to reduce ripples.
- Applications: Bridge rectifiers are used in high voltage applications, radio signal detection, and welding.
What is a Bridge Rectifier?
A bridge rectifier is a four-diode full-wave circuit. It sits beside half-wave rectifiers and two-diode full-wave rectifiers. The four diodes are D1, D2, D3, and D4. AC is applied at A and B. The load resistor RL is between C and D.
When A is positive and B is negative, D1 and D3 conduct. D2 and D4 are reverse biased.
Ideal current then follows D1 and D3 (Figure 2a). The voltage on RL is positive at D and negative at C.
When A is negative and B is positive, D2 and D4 conduct. D1 and D3 are reverse biased.
RL keeps the same polarity on both half-cycles. Figure 3 is that unipolar output.
However, it is to be noted that the bridge rectifier’s DC will be pulsating in nature. In order to obtain a pure form of DC, one has to use a capacitor in conjunction with the bridge circuit (Figure 4).
In this design, the positive pulse at the input causes the capacitor to charge through the diodes D1 and D3. However as the negative pulse arrives at the input, the charging action of the capacitor ceases and it starts to discharge via RL.
This results in the generation of DC output which will have ripples in it as shown in the figure. This ripple factor is defined as the ratio of the AC component to the DC component in the output voltage. In addition, the mathematical expression for the ripple voltage is given by the equation
Where,
Vr represents the ripple voltage.
Il represents the load current.
f represents the frequency of the ripple which will be twice the input frequency.
C is the Capacitance.
Further, the bridge rectifiers are primarily of two types, viz., Single-Phase Rectifiers and Three-Phase Rectifiers. In addition, each of these can be either Uncontrolled or Half-Controlled, or Full-Controlled.
Bridge rectifiers are chosen for the load current they must supply. They can be built with or without a transformer and are used on higher voltages than a simple half-wave stage.
However, here two diodes will be conducting for every half-cycle and thus the voltage drop across the diodes will be higher. Lastly one has to note that apart from converting AC to DC, bridge rectifiers are also used to detect the amplitude of modulated radio signals and to supply polarized voltage for welding applications.
