# Bridgeless Buck-Boost PFC Rectifier with Positive Output Voltage
## 1 Introduction  
The AC-DC rectifier with power factor correction (PFC) takes an important role not only in energy saving but also in reduction of the total harmonic distortion (THD). Harmonics standards, such as IEC61000-3-2 [1], JIS-C-61000-3-2, etc., are offered to limit the harmonics generated from the electronic products. For example, the electronic products with output power above 75 W need to pass the corresponding harmonics tests.  
There are two kinds of PFC rectifiers. The first kind is named passive PFC rectifier [2; 3], which is mainly built up by the inductor, the capacitor and the diode. This kind possesses advantages of circuit simplicity, low cost, and so on, but has disadvantages of large size, heavy weight, low efficiency, low circuit flexibility, and so on. Since the passive PFC rectifier does not work well, the second kind, named active PFC rectifier, is proposed [4; 5]. Generally, this kind is mainly constructed by the switch, the inductor, and the diode. The rectifier can make the input current tightly track the input voltage via the proper turning-on of the switch under different input voltages and various output loads. By doing so, the input current can easily meet the required harmonics standard. Compared with the passive PFC rectifiers, the active PFC rectifier has many advantages, such as small size, light weight, high power density, high PF, low THD, etc.  
There are three kinds of non-isolated converters widely utilized in the active rectifier: boost, buck, and buck-boost converters. Among them, the active PFC boost rectifier is commonly employed [6; 7; 8]. The key merit of this kind is that the current in the input inductor operates in the continuous conduction mode (CCM), thereby obtaining a high PF and a low THD. However, such a kind can be used only under the condition that the output voltage is larger than the peak value of the input voltage.  
Consequently, the active buck PFC rectifier is presented [9; 10; 11]. Such a rectifier can transfer a high input AC voltage to a low DC voltage. However, as the input voltage is lower than the outputvoltage, there is no input current, thus making zero-crossing distortion occur. Consequently, even if this rectifier operates in the CCM, the PF is relatively low and the THD is relatively high.  
Based on the aforementioned, the active buck-boost PFC rectifier is proposed [12; 13; 14]. In the CCM, such a PFC rectifier possesses relatively high variations in output voltage due to step-up/step-down of the input voltage. However, the output voltage of this rectifier is negative. Consequently, its industrial applications are limited.  
On the other hand, the power loss in low-frequency diodes of the traditional active PFC rectifier is huge. Hence, to remove this diode loss, some researchers present bridgeless active PFC rectifiers using high-frequency diodes and switches [15; 16; 17].  
Accordingly, a bridgeless buck-boost PFC rectifier with positive output voltage is proposed herein. This circuit is derived from the circuit shown in [17] by [PERSON]; [PERSON] The total component count of the proposed circuit is the same as that of the circuit shown in [17]. Basically, there is a difference in specifications between the proposed circuit and the circuit shown in [17], and the comparison between the two is not easy. However, from the point of view of voltage gain in the BCM or CCM, the former has a value of D/(1-D), locating between zero and infinity, where D is the duty cycle, and the latter has a value of 2D, locating between zero and two. This means that the former has relatively low zero crossover distortion as compared to the latter. Namely, the proposed circuit has better performance of PFC and THD than the circuit shown in [17] has. Furthermore, in the proposed circuit, the rectification switches \(S_{1}\) and \(S_{2}\) are back-to-back cascaded in the opposite direction, and thus only one gate driver is required.