Rectifiers are used to convert an AC power to DC power. Among the rectifiers, the bridge rectifier is the most efficient rectifier circuit, and 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. In the next few sections, let us learn more about its construction, working, and more.
Construction of Bridge Rectifier
The construction of a bridge rectifier is shown in the figure below. The bridge rectifier circuit is made of four diodes D1, D2, D3, D4, and a load resistor RL. The four diodes are connected in a closed-loop configuration to efficiently convert the alternating current (AC) into Direct Current (DC). The main advantage of this configuration is the absence of an expensive center-tapped transformer. Therefore, the size and cost are reduced.
The input signal is applied across terminals A and B, and the output DC signal is obtained across the load resistor RL connected between terminals C and D. The four diodes are arranged in such a way that only two diodes conduct electricity during each half cycle. D1 and D3 are pairs that conduct electric current during the positive half cycle/. Likewise, diodes D2 and D4 conduct electric current during a negative half cycle.
Working
When an AC signal is applied across the bridge rectifier, terminal A becomes positive during the positive half cycle while terminal B becomes negative. This results in diodes D1 and D3 becoming forward-biased while D2 and D4 become reverse-biased.
The current flow during the positive half-cycle is shown in the figure below:
During 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 to be reverse-biased.
The current flow during the negative half cycle is shown in the figure below:
From the figures given above, we notice that the current flow across load resistor RL is the same during the 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 diodes’ direction is reversed, we get a completely negative DC voltage.
The output waveforms of the bridge rectifier are shown in the below figure.
Characteristics of Bridge Rectifier
Ripple Factor
The smoothness of the output DC signal is measured by a factor known as the ripple factor. The output DC signal with fewer ripples is considered a smooth DC signal while the output with high ripples is considered a high-pulsating DC signal.
Peak Inverse Voltage
The maximum voltage that a diode can withstand in the reverse bias condition is known as a peak inverse voltage.
Efficiency
The rectifier efficiency determines how efficiently the rectifier converts Alternating Current (AC) into Direct Current (DC). Rectifier efficiency is defined as the ratio of the DC output power to the AC input power.
Advantages
- The efficiency of the bridge rectifier is higher than the efficiency of a half-wave rectifier. However, the rectifier efficiency of the bridge rectifier and the center-tapped full-wave rectifier is the same.
- The DC output signal of the bridge rectifier is smoother than the output DC signal of a half-wave rectifier.
Disadvantages
- When more diodes are used more power loss occurs. In a center-tapped full-wave rectifier, only one diode conducts during each half cycle. But in a bridge rectifier, two diodes connected in series conduct during each half cycle. Hence, the voltage drop is higher in a bridge rectifier.
Applications
- Electric welding requires a steady supply of DC in a polarized manner, this is possible by the full-wave rectifying circuit.
- Because of the efficient nature of the bridge rectifier, it is preferred as part of the various appliances’ power supply units.
- The high AC voltage can be converted into a low DC value with the capable nature of the bridge rectifier.