## 1 Introduction  
Conventional AC/DC rectifiers, which consist of a bridge rectifier and smoothing capacitors, can be used to supply power in telecom applications, but the circuit performance and fixed control parameters in these rectifiers lead to high total harmonic distortion (THD), high power losses, and reduced conversion efficiency, especially in high-power-density applications. So, the high-power factor and efficiency requirements in telecom applications limit the use of such conventional rectifiers [1]. Currently, to offer efficient high-power-density power supply, the active-controlled AC/DC converters, with high power density based on the boost converter technique, have been widely used to regulate the power factor (PF), reducing THD and the circuit power losses, and increasing the conversion efficiency [2, 3]. The AC/DC power supply with two stages, as illustrated in Figure 1, is the optimal configuration to obtain high values for the input PF and power conversion efficiency. Two-stage active AC/DC telecom power supply consists of (1) the active power factor correction (PFC) stage to offer input current with high PF and (2) the DC/DC output converter stage, which is used to regulate the bus voltage of the PFC converter stage (320-410 V) to the distribution load level (45-63 V) for telecom applications [4]. According to the power applications, many types of PFC converters are widely used, such as the conventional [5, 6, 7], bridgeless [8, 9], and the interleaved [10, 11] PFC boost converters. For telecom applications, the conventional PFC boost converter is the most commonly used circuit because of its good performance, low cost, simple operations, and lower requirements for the power and control circuit designs [1, 12]. The target of this study was to improve the performance of the conventional PFC stage telecom power supply by optimizing the control of the boost converter controllers to produce a converter with a unity power factor by reducing the THD of the input supply current. A PFC boost converter controlling circuit can be implemented using digital or analog techniques. Controlling the circuit using analog integrated circuits (IC) offers an economic design of the converter; otherwise, it will have some disadvantages compared with the digital micro-controller unit (MCU), such as slow response, low operating temperature, and fixed control parameters. Digital MCU offers a high-speed response, flexible adjustment, and programming of the control techniques [13]; however, the price of the measurement sensors required for the interface between the converter power circuit and DSP MCU is high compared with sensors for interfacing with analog control IC. The conventional PFC boost converter consists of power and control circuits, where the power circuit contains a bridge rectifier, energy storage inductor, single switch or multiple switches connected in parallel (to increase the converter current rating), fast switching diode, and an output bulk capacitor. The PFC boost converter control circuit usually implements two control loops: the inner current-control loop to control the inductor current, which makes the input current follow the input voltage and maintain the circuit PF at higher values, and the outer voltage loop, which maintains the output voltage value as the specified load value. Usually, these control loops are implemented using PI controllers. For the output voltage control loop, the PI controller is enough to regulate the output voltage to the specified value [14], but for the inductor current-control loop, the slow response of the PI current controller at the current zero-crossing point distorts the inductor current, which leads to increasing the THD of the supply current [15]. Increasing the THD in the converter circuits causes higher power losses in all circuit components; further, it can lead to high current stresses and failures of the system insulation and protection [16].