## 3 Telecom AC/DC PFC Boost Converter Operation Principle and Design  
Figure 3 shows the schematic circuit of the PFC boost converter, which usually consists of an electro-magnetic interface (EMI) filter connected to the AC input power source, bridge rectifier, and the boost converter unit, which is the main part of the PFC boost converter. The boost converter employed in this study works in current continuous conduction mode (CCM); this topology is the conventional and most used in telecom applications due to it is simple design, reliability for higher power applications, and low price compared with the other PFC topologies [1; 12]. The boost converter unit consists of three main parts: the storage energy part, represented by the inductor (L\({}_{\text{b}}\)); the switching elements, represented by high voltage switch (Q\({}_{\text{b}}\)); high-speed switching diode (D\({}_{\text{b}}\)); and the output filtering capacitor C\({}_{\text{b}}\).  
The following paragraphs present the operation principle and the design of the main components of the single-phase CCM-boost converter.  
Figure 4 depicts the schematic circuits of the different operation modes for the CCM-boost converter. When the switch (Q\({}_{\text{b}}\)) is closed, as shown in Figure 4a, the current flows through the energy storage element (L\({}_{\text{b}}\)) in the direction marked by the red dotted line. At this moment, the energy is storage in the inductor, generating a magnetic field. When Q\({}_{\text{b}}\) is opened, as shown in Figure 4b, the current circuit impedance increases, thereby reducing the current, and the magnetic field previously created is reduced to maintain the current toward the load, as also marked by the red dotted line. Thus, the polarity of the inductor voltage is reversed, which places the two sources in series, providing a higher voltage to charge the capacitor (C\({}_{\text{b}}\)) through the high-speed switching diode (D\({}_{\text{b}}\)).  
The three parts of the boost converter should be optimally designed to maintain the circuit-specified ripple currents, reduce the voltage stress in the switching elements during the converter operation, and maintain the output voltage with the ripple value required for telecom applications.  
Figure 4: CCM-boost converter operation modes. (**a**) Switch Q\({}_{\text{b}}\) closed, (**b**) Switch Q\({}_{\text{b}}\) opened.  
Figure 3: Schematic diagram of the conventional AC-DC PFC boost converter.  
The PFC boost converter inductor (\(\text{L}_{\text{b}}\)) was designed based on the specified circuit ripple current (%Ripple) and the corresponding input and output voltage conditions [29]. PFC control circuits are usually designed to offer good performance for a wide range of input AC voltage (85-265 V). Using these design specifications, \(\text{L}_{\text{b}}\) can be calculated as  
\[\text{L}_{\text{b}}=\ \frac{1}{\text{\%Ripple}}\times\frac{1}  
generate the voltage error signal, which is modified with the input sinusoidal voltage (V\({}_{\text{in}}\)) to generate the reference current (I\({}_{\text{ref}}\)) value for the inner control loop, as depicted in the control blocks in Figure 6. The inner loop is used to make the inductor current (I\({}_{\text{Lb}}\)) track the reference current (I\({}_{\text{ref}}\)); the inductor current is the DC value of the input supply current, so that any distortion in the inductor current will affect in the sinusoidal shape of the input supply current.  
Usually, the PI controller is enough to regulate the output voltage to the reference limit, having good performance and fast response [14], so in the conventional and proposed control circuits, the same PI controller was used in the voltage control loop.