A rectifier is a circuit that converts alternating current (ac) into direct current (dc). Generally, rectifiers are two types, half-wave and full-wave rectifiers. A full wave rectifier is a circuit that rectifies the complete cycle of ac supply.
Thus a full wave rectifier provides continuous current to flow in one direction through the load. There are two types of full-wave rectifier circuits they are center-tapped and bridge-type full-wave rectifiers.
The center-tapped and bride-type rectifiers are two different types of circuit constructions that converts both positive and negative cycles of ac into dc. A center-tapped full-wave rectifier comprises two diodes and a center-tap transformer, whereas a bridge rectifier uses four diodes for rectification. Let us see the difference between a center tap and a bridge-type full wave rectifier in detail.
Difference Between Full Wave Center-Tapped and Bridge Rectifier:
| Parameter | Center-tapped Rectifier | Bridge Rectifier |
|---|---|---|
| Definition | A center-tapped rectifier is a type of full-wave rectifier that uses two diodes and a center-tap transformer for the conversion of ac to dc. | A bridge rectifier is also a full wave rectifier where four diodes are connected in a bridge configuration. |
| Circuit Complexity | The circuit of a center-tapped rectifier is simple. | The circuit of a bridge rectifier is complex. |
| Number of Diodes | A center-tapped rectifier uses only two diodes. | A bridge-type rectifier requires four diodes. |
| Need for Transformer | A center-tap rectifier requires a transformer that provides a center tap on the secondary winding. | There is no necessity for a transformer in a bridge rectifier circuit. |
| Transformer Size Requirement | The kVA rating of the transformer required for a center tap rectifier is more. | The transformer size requirement for a bridge rectifier is less compared to a center-tapped rectifier. |
| Transformer Utilization Factor | The transformer utilization factor of a center-tapped rectifier is 0.573. | The transformer utilization factor of a bridge rectifier is 0.8106. |
| Voltage Drop across the diodes | Since there are only two diodes present in a center-tapped rectifier, the voltage drop across the diodes is less. | High voltage drop because a bridge rectifier uses four diodes. |
| DC Output Voltage | 2Vm/π | 2Vm/π |
| Form Factor | The form factor of a center-tapped rectifier is 1.11. | The form factor of a bridge rectifier is the same as a center-tap rectifier i.e., 1.11. |
| Output Frequency | The output frequency of a center-tapped rectifier is double that of ac input frequency i.e., 2f. | The output frequency is same as a center-tap rectifier i.e., 2f. |
| Ripple Factor | The ripple factor of a center-tapped rectifier is 0.48. | The ripple factor of a bridge rectifier is 0.48. |
| Efficiency | The maximum efficiency of a center-tapped rectifier is 81.2%. | The maximum efficiency of a bridge rectifier is same as a center-tapped rectifier i.e., 81.2%. |
| Peak inverse voltage (PIV) | The peak inverse voltage across the diode in a center-tapped rectifier is double the peak voltage of the transformer’s secondary winding. | The peak inverse voltage across the diode in a bridge rectifier is equal to the peak voltage of the transformer’s secondary winding. |
| Cost | The cost of a center tap rectifier is high. | The cost of a bridge rectifier is less due to the absence of a center-tap transformer. |
Full Wave Center-Tapped Rectifier:
A center-tapped full-wave rectifier uses two semiconductor diodes in combination with a center-tap transformer. In this type of circuit configuration, ac supply source is given to the primary winding of a center-tap transformer. Two diodes are connected to the two ends of the transformer secondary winding and the other ends of the two diodes are connected to the common load which is connected to the center-tap terminal.
During the positive half cycle of the ac input supply, diode D1 comes into forward bias i.e., it acts as a closed switch, and diode D2 is reverse biased i.e., it acts as an open switch. Thus load current flow from terminal A, through the diode D1, to the R-load, and return back through the center-tap terminal C.
When the negative half cycle of ac input appears, diode D2 acts as a closed switch and diode D1 acts as an open switch. Thus load current flow from terminal B, through the diode D2, to the R-load, and return back through the center-tap terminal C.
In this way, both positive and negative half cycles of ac supply are converted into pulsating dc and applied to the load. The drawbacks of a center-tapped rectifier are only half of the secondary winding is utilized at a time and the peak inverse voltage across the diode is twice the secondary winding peak voltage.
Full Wave Bridge Rectifier:
A bridge rectifier is also a full-wave rectifier where both the half-cycles of ac supply are rectified. In this type of rectifier circuit, four diodes are connected in a bridge configuration as shown below. A transformer can be used at the input and output side to step-up or step-down the voltage level.
When the positive half-cycle of ac input is applied to the rectifier, diodes D1 and D2 are forward-biased, while diodes D3 and D4 are reverse-biased. Thus during the positive half cycle load gets connected across the supply source through diodes D1 and D2.
When the negative half-cycle of ac input is applied to the rectifier, diodes D3 and D4 are forward biased and diodes D1 and D2 are reverse biased. Thus during the negative half cycle, load current flows through diodes D3 and D4.
In this way for every half cycle, two diodes will be in conduction obtaining a pulsating dc output. The main advantage of bridge configuration over center-tapped configuration is reduced peak inverse voltage across diodes and improved transformer utilization factor.
Key Differences Between Center-Tapped and Bridge Rectifiers:
- A bridge rectifier circuit requires four diodes whereas a center-tapped rectifier uses only two diodes.
- A center-tap rectifier requires a transformer whose secondary winding is center-tapped. For a bridge rectifier, there is no necessity for a transformer.
- In a center-tapped rectifier, the peak inverse voltage across diodes will be twice the transformer’s secondary voltage. Whereas in a bridge rectifier, the peak inverse voltage across diodes will be equal to the transformer’s secondary voltage. Thus bridge rectifiers can be used for high-voltage applications.
- Due to the high peak inverse voltage across diodes in a center-tapped rectifier, the diodes used should have a breakdown voltage twice that of a bridge rectifier.
- The voltage drop across the diodes in a center-tapped rectifier is less than in the bridge rectifier because only two diodes are used in the center-tapped rectifier.
- In a center-tapped rectifier, only half of the secondary winding is used at a time. Thus the transformer size (kVA rating) required for a center-tap rectifier is more than the bridge rectifier.
- The transformer utility factor of a bridge rectifier is more than the center-tap rectifier.
Conclusion:
Therefore center-tap and bridge rectifiers are two different types of full-wave ac to dc converters with different circuit configurations and working. Compared to a center-tapped rectifier, a bridge rectifier has more advantages like reduced peak inverse voltage and improved transformer utilization factor.