A Critical Conduction Mode, Active Power Factor Correction Circuit Design,

In recent years, people pay an increasing attention to harmonic pollution of power supply, and require power system that have characteristics of low harmonic and high power factor. Furthermore, it is highly regarded in the world, Harmonic standards have been promulgated by Institute of Electrical and Electronics Engineers (IEEE), International Electrotechnical Commission (IEC) and international council on large electric system (CIGRE) in order to strictly limit harmonic content that are produced by electrical appliances and other nonlinear loads. Accordingly, it is a pressing demand using power factor correction to meet harmonic pollution in the standards.Owing to passive power factor correction (PPFC) has badly repressed effect ang low power factor, active Power Factor Correction (APFC) is an effective technique for restraining harmonic current , improve power factor and increasing the power supply network efficiency. Therefore, active solution has been widely applied.A boost mode active power factor correction circuit operating in critical conduction mode by using EPISIL DF1 5μm 40V BJT technology is presented in this thesis. Critical conduction mode operation is the most popular solution for low power applications, this control method has the following advantages: simple control scheme (the application requires few external component), ease of stabilization (the boost keeps a first order converter and there is no need for ramp compensation), zero current turn on (the MOSFET turn on when the diode current reaches zero). The input supply voltage is 220V alternating current which frequency is 50 hertz. The output power is 100W, and its output voltage is 410V with 9V output voltage ripple. This circuit can operate in the temperature range of -25℃to 125℃. Power factor can reach 0.97, the efficiency is not lower than 0.88. It also includes under voltage lockout.In this paper, first, the function of primary circuit modules are analyzed. Secondly, the characteristic of boost converter and the critical conduction mode of active power factor correction are analyzed and compared, at the same time, the working theorys of current and voltage loop are analyzed. Thirdly, the switching frequency variations of MOSFET versus the AC line amplitude, the input power and within the sinusoid are compared. Based on the whole chip function requirements, sub-block design and simulation were completed, including analog multiplier, error amp, voltage reference, current sense comparator and dynamic over voltage protection. At last, the whole chip function simulation and some typical performance characteristics simulation were presented.