Basic Concept of Rectification in Electronics:
We are already familiar with the difference between AC (Alternating Current) voltage source and DC (Direct Current) voltage source. The AC moves in both direction while DC moves in one direction (See Fig 1). The electronics devices need a constant source of DC including consumer electronic products like LED TV, mobile phones, telephone,DVD etc. So as electronics engineer or technician it is important to understand how does rectifier circuit work. The voltage available to us from power generation companies is of AC form. So we need a rectification from AC into DC.
Fig. 1: AC vs DC
Block Diagram of Complete Rectifier Circuit:
- Transformer is used to step down the supply voltage
- Rectifier converts AC into pulsating DC
- Filter makes the pulses more smooth
- Regulator keeps a constant supply
Types of Rectifier Circuits:
There are basic two types of rectifier circuits
- Half Wave Rectifier
- Full Wave Rectifier
Fig. 3: Half-wave and Full-wave Rectifier Concept
The half-wave rectifier design has only one diode connected to the supply and the load as shown in fig. 4(a),(b) below. During the positive cycle the diode is forward bias and conducts current to the load. Whereas during negative cycle diode becomes reverse bias and doesn’t allow current to flow towards load.
During the positive cycle the diode is forward bias and conducts current to the load
Fig-4a: Half-wave Rectifier Positive Cycle
Whereas during negative cycle diode becomes reverse bias and doesn’t allow current to flow towards load.
Fig-4b: Half-wave Rectifier Negative Cycle
The major disadvantage of half wave rectifier is we get large fluctuations. In addition to the variation in amplitude of AC voltage, diode is off for almost half of the time due to negative cycle. Hence we get half of the energy as compared to full-wave rectifier.
The full-wave rectifier allows current to flow towards load even there is a negative cycle. Lets see how its various types works for both cycles i.e positive and negative
Center-Tapped Full-Wave Rectifier
Center-tapped full-wave rectifier used two diodes and a transformer with a center tap at secondary winding
During positive cycle diode D1 is working and D2 is off as shown in fig. 5a
Fig-5a: Center.tap Rectifier Positive Cycle
When negative cycle come, polarity reverses so D2 starts working and D1 gets off. But the current flows as the same direction through the load as that of positive cycle.See fig. 5b
Fig-5b: Center-tap Rectifier Negative Cycle
2. Full-Wave Bridge Rectifier:
The full wave bridge rectifier uses a combination of four diodes. So it eliminates the draw back of center-tap rectifier i.e the size of the transformer in high power applications.
When positive cycle come D1 and D2 conducts. But D3 and D4 are off as shown in fig 6a
Fig-6a: Bridge Rectifier Positive Cycle
When negative cycle comes D1 and D2 are off. On the other hand D3 and D4 starts working. See fig 6b
Fig-6b: Bridge Rectifier Negative Cycle
You can observe that current flows through the load have same direction for both cycles
Below is the complete video lecture on rectifier circuits in Urdu/Hindi