Bridge Rectifier: Working, Properties, Advantage and Disadvantage

The rectifiers are used to convert an AC power to a DC power.Half-wave, full-wave, and bridge rectifiers are the three most common types of rectifiers. All of these rectifiers have the same fundamental purpose of current conversion, however they do not transfer current from AC to DC efficiently.

We can define bridge rectifiers as a type of full-wave rectifier that uses four or more diodes in a bridge circuit configuration to efficiently convert alternating (AC) current to a direct (DC) current.

Bridge Rectifier

Rectifiers are commonly used for converting AC power into DC power.

The primary function of bridge rectifier is to convert AC power to DC electricity. For improving the bridge rectifier, a filter is also use in the circuit. Many electronic circuits require a rectified DC supply to power the electronic components from the available AC mains supply..

Bridge rectifiers are a form of Full Wave Rectifier which convert alternating (AC) current to direct (DC) current by using four or more diodes in a bridge circuit.

Construction

The circuit of the bridge rectifier is made of 4 diodes (D1, D2, D3 and D4 ) and a load resistor RL. These four diodes are connected in a closed-loop configuration to convert the alternating current (AC) into Direct Current (DC). The main advantage of this configuration is the absence of the expensive center-tapped transformer.

The input signal is applied across terminals A and B, and the output DC signal is obtained across the load resistor RL which is connected between terminals C and D. The four diodes are arranged in this way that only two diodes conduct electricity during each half cycle. D1 and D3 are pairs which conduct electric current during the positive half cycle. Diodes D2 and D4 conduct electric current during a negative half cycle.

Working

When an AC signal is applied across the bridge rectifier then terminal A becomes positive during the positive half cycle while terminal B becomes negative. This results in diodes D1 and D3 becoming forward biased and diodes D2 and D4 becoming reverse biased.

The current flow during the positive half-cycle is shown –

In the negative half-cycle, terminal B becomes positive while terminal A becomes negative. This causes diodes D2 and D4 to become forward biased and diodes D1 and D3 become reverse biased.

The current flow during the negative half cycle is shown

Here, we notice that the current flow across load resistor RL is the same during both positive and negative half-cycles. The polarity of output DC signal may be completely positive or negative. In our case, it is completely positive. If the diodes direction is reversed we get a complete negative DC voltage.

Thus, a bridge rectifier allows to pass electric current through both positive and negative half cycles of the input AC signal.

Properties of Bridge Rectifier

Ripple Factor

The smoothness of the output DC signal is what the ripple factor is. Smooth DC signals have fewer ripples, while pulsing DC signals have more. A ratio of ripple voltage to pure DC voltage can be defined as ripple factor.

The Formula for Ripple Factor is given by:

=

Where

V_rms= Root Mean Square Voltage

V_DC = Average Voltage of DC Supply

Generally the ripple factor for a Bridge Rectifier is considered to be (0.48).

Efficiency

Rectifier efficiency – It is the ratio of the (DC) output power to the (AC) input power.

η = DC output power / AC output power

The max. Value of the efficiency of bridge rectifier is (81.2%)

Advantage of Bridge Rectifier

The efficiency of a bridge rectifier is higher than that of a half-wave rectifier. The efficiency of a bridge rectifier is comparable to that of a center-tapped full-wave rectifier.

In comparison to a half-wave rectifier’s output DC signal, the bridge rectifier’s output signal is smoother.

The flow of current is allowed throughout both negative and positive cycles, unlike a half-wave rectifier. As a result, the output DC signal is nearly identical to the input AC signal.

Disadvantage of Bridge Rectifier

It has a complicated circuit made up of four distinct diodes.

Bridge rectifier have high power loss.

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