# PFC Single-Phase AC/DC Boost Converters: Bridge, Semi-Bridgeless, and Bridgeless Topologies
## 2 Categorization of Bridge Boost Converter Topologies
### Conventional PFC Topology with Bidirectional Switch  
Figure 5 shows the BBC Conventional PFC Topology with Bidirectional Switch [37; 83]. In this topology, inductors \(L_{1}\) and \(L_{2}\) (\(L_{1}=L_{2}\)) are used as coupling inductors, while the bidirectional switch composed of \(Q_{1}\) and \(Q_{2}\) is on the AC side of the converter. For an appropriate operation, \(D_{1}\) and \(D_{4}\) must be fast-recovery diodes. This topology permits the reduction of the common mode noise; however, an EMI filter in the input of the converter is still necessary. One advantage is that the same control signal can be used for controlling \(Q_{1}\) and \(Q_{2}\). It is important to mention that \(Q_{1}\) and \(Q_{2}\) must be installed in inverted order to avoid reverse currents in the operation when both switches are open. In addition, stages of control and power should be isolated as recommended in [36]. In this topology, a resonant circuit for soft switching in order to reduce switching power losses s recommended [84; 85; 86].  
Figure 4: Hybrid Interleaved PFC topology.  
Different configurations were proposed to enhance the performance of the bidirectional BBC topology [83; 87]. The PFC Topology with Bidirectional and flexible switches is depicted in Figure 6a. This converter includes (\(Q_{3}\) and \(Q_{4}\)) as auxiliary switches and also a split DC link bus configuration (\(C_{1}\) and \(C_{2}\)). \(Q_{3}\) and \(Q_{4}\) allow supplying the converter with two levels of input voltage, and both auxiliary switches are open or closed at the same time facilitating the control strategy. This converter is only recommended for low voltage and power applications since the bidirectional switches increase power losses and need a robust soft switch circuit for the management of high currents. The BBC PFC Interleaved Topology with Bidirectional switch is depicted in Figure 6b. This converter is only suggested for low voltage and low power applications since it requires a great quantity of semiconductors that need independent soft switching, isolation, and drivers--so that conventional interleaved (Section 2.2) BBC complies with the same function with less components and control complexity.  
Bidirectional switch topologies are only suggested for low voltage and low power applications since they require additional switches which increase the cost of implementation and operation. For medium and high power applications, bidirectional topologies have a low efficiency because the converter currents have only one path of flow, not splitting in each half-cycle as in the previous converters. Consequently, thermal stress and power losses increase, which yields the increasing of differential noise [36; 37; 83; 88]. Additionally, it is important to reduce switching losses in bidirectional topologies for two reasons: (1) bidirectional converters have more switches than other topologies for the same function, (2) bidirectional switches are in the converter input (before the rectifier bridge), where the voltage is low and the input current is high; then, bidirectional switches must be more robust than those located after the rectifier bridge.  
Figure 5: Conventional PFC topology with a bidirectional switch.  
Figure 6: BBC converter with bidirectional switch: (**a**) bidirectional and flexible switches; (**b**) bidirectional and interleaved.