Full Wave Rectifier - Conceptual Review | Basic Electronics

Summary

This tutorial explains the operation of a full-wave bridge rectifier, which rectifies both positive and negative half-cycles of AC input, making it more efficient than a half-wave rectifier. It covers the use of four diodes in a bridge configuration to convert AC into pulsating DC, with a discussion on the voltage drops across diodes and the calculation of the average output voltage. The tutorial also touches on the peak inverse voltage (PIV) and provides practical considerations when selecting diodes. The focus is on understanding the bridge rectifier's key components and performance in power supply applications.

Takeaways

• 😀 Half-wave rectifiers only rectify the positive half-cycle of AC input, while full-wave rectifiers rectify both positive and negative half-cycles.
• 😀 Full-wave rectifiers are more efficient than half-wave rectifiers because they use the entire 360-degree input cycle, resulting in higher average output voltage and frequency.
• 😀 There are two types of full-wave rectifiers: bridge and center-tapped. This tutorial focuses on the bridge type.
• 😀 A half-wave rectifier uses a single diode, while a bridge full-wave rectifier uses four diodes arranged in a bridge topology.
• 😀 During the positive half-cycle, the current flows through diodes D1 and D2, while during the negative half-cycle, the current flows through diodes D3 and D4.
• 😀 The output of a bridge rectifier is pulsating DC, but its average voltage is higher than that of a half-wave rectifier.
• 😀 The average output voltage of a full-wave rectifier can be calculated using the formula: V_avg = 2 * V_peak / π.
• 😀 In an ideal scenario, the peak output voltage of a bridge rectifier equals the peak voltage of the transformer's secondary winding, but in reality, there is a 0.7V voltage drop per diode in the circuit.
• 😀 The actual peak output voltage is 1.4V less than the transformer’s peak voltage due to the combined voltage drop across two conducting diodes in the bridge rectifier.
• 😀 The peak inverse voltage (PIV) that the diodes must withstand is the sum of the peak voltage across the load and the forward voltage of one diode. To ensure safety, diodes should have a PIV rating at least twice this value.

Q & A

What is the key difference between half-wave and full-wave rectifiers?

The main difference is that half-wave rectifiers only rectify one half-cycle (positive or negative) of the AC input, while full-wave rectifiers rectify both the positive and negative half-cycles, making them more efficient.

Why are full-wave rectifiers preferred over half-wave rectifiers in most applications?

Full-wave rectifiers are preferred because they rectify both the positive and negative half-cycles of the AC input, providing a more efficient and stable DC output with a higher average voltage and frequency.

What are the two types of full-wave rectifiers?

The two types of full-wave rectifiers are the bridge rectifier and the center-tapped rectifier.

How many diodes are used in a bridge full-wave rectifier and why?

A bridge full-wave rectifier uses four diodes arranged in a bridge topology to rectify both the positive and negative half-cycles of the AC input.

During the positive half-cycle, which diodes in a bridge rectifier are forward-biased?

During the positive half-cycle, diodes D1 and D2 are forward-biased, allowing current to flow through the load.

What happens to the diodes during the negative half-cycle in a bridge rectifier?

During the negative half-cycle, diodes D1 and D2 become reverse-biased, while diodes D3 and D4 become forward-biased, allowing current to flow through the load in the same direction as during the positive half-cycle.

What is the significance of the voltage drop across the diodes in a bridge rectifier?

The voltage drop across the diodes reduces the peak output voltage. For a silicon diode, the drop is typically 0.7V, and since two diodes conduct at a time, the total voltage drop is 1.4V, lowering the peak output voltage by this amount.

How is the average output voltage of a full-wave rectifier calculated?

The average output voltage of a full-wave rectifier can be calculated using the formula: V_avg = (2 × V_peak) / π, where V_peak is the peak voltage of the transformer’s secondary winding.

What is the Peak Inverse Voltage (PIV) in a bridge rectifier?

The Peak Inverse Voltage (PIV) is the maximum reverse voltage that a diode must withstand when it is in a reverse-biased condition. For safety, the diodes should have a PIV that is at least twice the value of the peak voltage across the load plus the forward voltage of one diode.

How do the diodes in a bridge rectifier contribute to the unidirectional DC output?

The diodes in a bridge rectifier ensure that, regardless of whether the AC input is in the positive or negative half-cycle, the current always flows through the load in the same direction, producing a unidirectional, though pulsating, DC output.