# Single-Stage Step-Down Power Factor Corrector without Full-Bridge Rectifier
## 1 Introduction  
Thanks to the rapid development of technology and power electronics, low-frequency harmonic currents created by the characteristics of nonlinear loads of power electronics products flow into the power system in large quantities, thereby leading to increasingly serious harmonic pollution of the power system. As generally acknowledged, the harmonic current will change the output voltage waveform of the power system. When the harmonic current generated is larger or exceeds the permissible value, it may cause other products in its vicinity to operate incorrectly, measurement errors, efficiency degradation, or even burnout. Therefore, harmonics are regulated in various countries around the world. The International Electrotechnical Commission (IEC) in Europe has issued the IEC61000-3-2 harmonic standard [1], and Japanese specifications have also been issued, JIS-C-C. The Japanese authority also promulgated the JIS-C-61000-3-2 standard [2], which formally regulates the harmonics generated by electronic equipment products, and stipulates that all electronic equipment products with an output power of 75 W or more must pass a harmonics test. In order to improve harmonic and power-factor problems, it is necessary to add a power factor correction (PFC) circuit. The main function of this circuit is to make the input voltage and input current in the same phase, so that the load observed by the utility is similar to the resistive load. They can be categorized into passive and active power factor correction circuits, depending on the components used. Passive power factor correctors [3] are composed of passive components, including inductors, capacitors, diodes, etc. These circuits have the advantages of a simple circuit structure, low cost, and low electromagnetic interference, etc. However, they are bulky, heavy, inefficient, and lack flexibility in the circuits. That is to say, the passivepower factor correction is ineffective, and they are not suitable for today's stringent power factor requirements. Due to the above disadvantages of passive PFC rectifiers, active PFC rectifiers were developed. Generally, the circuit components of the active PFC rectifier [4] include switching switches, inductors, and diodes, etc. According to the input conditions and output load requirements, the timing of the main power switch can be controlled by appropriate feedback compensation control and pulse width modulation (PWM) to make the phase of the input current closely follow the phase of the input voltage, so as to stabilize the output voltage, as well as to control the input current waveform to meet the harmonic specification. Commonly used single-stage active power PFC rectifiers are classified into two types, boost-derived and buck-derived, among which the boost PFC circuits have been widely used [5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18]. The boost PFC rectifier has the following advantages: (i) the inductor is directly connected to the power supply at the input end, and in the continuous conduction mode (CCM), the input current is continuous; so that the input current spike can be suppressed, the electromagnetic interference is smaller, and the power factor can be higher; (ii) the main power switch driver does not need to be isolated, so that the driver circuit is easy to design; (iii) the input current is the inductor current, which makes it easy to realize current mode control; (iv) it has a high output voltage, so compared to other circuit topologies, it has a better hold-up time after a power failure when using the same capacitor size. However, because of the higher output voltage, there are some drawbacks: (i) the voltage tolerance of the power switch has to be large enough; (ii) to meet the demand of the back-end load voltage, an additional regulation stage or isolation step-down circuit is required, thereby increasing the cost; and (iii) the high output voltage is prone to causing a high common-mode noise.