The English full name of PFC is "power factor correction", which means "power factor correction". Power factor refers to the relationship between effective power and total power consumption (apparent power), that is, the ratio of effective power divided by total power consumption (apparent power). Basically, power factor can measure the degree of effective utilization of power. The larger the power factor is, the higher the power utilization is.
The common working modes of PFC topology are CCM current continuous type, DCM discontinuous type and CRM critical type. PFC topology has higher requirements for MOS transistor. Under the condition of ensuring system efficiency and temperature rise, it is necessary to improve system stability as much as possible. In order to smooth the ripple of 100hz-120hz AC rectifier, the response time of PFC topology must reach several 10ms. If the control circuit and IC are not specially optimized, PFC topology will produce a large impact current during the start-up process, which can reach 5-10 times of the normal working current. Especially in the repeated switching process, it is a more severe test for MOS transistor. The MOS transistors in PFC topology are connected between high voltage and ground. In safety test, the EAS capability of MOS transistors is also an important reference to evaluate its reliability. Therefore, the switching characteristics (CISS), EAS capability, surge resistance and ESD protection capability of MOS should be taken into consideration when selecting MOS in PFC circuit.
At present, countries in Europe and the United States need to add PFC circuit when the input power of power supply is greater than 75W. With the refinement of the structure of electrical products, the requirements of power factor, efficiency and power density of power supply products are higher and higher. The traditional Si FRD devices are difficult to meet the demand, and SiC materials can meet the demand.
PFC circuit is generally used in European and American countries for power input power greater than 75W power supply, such as PC power supply, TV power supply, power supply, lighting power supply, adapter, server, charging pile power supply, etc. For power supply of control system, the capacity varies from several hundred watts to several thousand watts. For power supply products with 90V to 264Vac input, PFC boost diode with high-speed switching performance and diode with withstand voltage above 500V are generally required. As shown in Fig. 1 and 2, D1 is the application schematic diagram of SiC diode applied to boost.
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