HARMONICS AND POWER-FACTOR IMPROVEMENT TECHNOLOGY FOR COMPUTER POWER-SUPPLY

In recent years, harmonic current leaking from electronic apparatus has been attracting attention as a problem adversely affecting the common power supply system. IEC (International Electro-technical Commission) has established the harmonic wave control standard in WGI of SC77A, and is now studying the revision of the IEC 555-2 standard. In Japan, the guideline for harmonic wave control is also being studied on the basis of the revision plan of the IEC 555-2 standard. On the other hand, the power factor of equipment connected to the single-phase commercial power supply is generally low at about 60%. Accordingly, computer users are requesting improvement of the power factor for energy saving and reduction of equipment size. These two problems of harmonic current and low power factor are caused by the use of the capacitor input smoothing circuit. Because the Switching Regulator Module (SRM) in the power supply units that authors have so far developed for computers adopts the capacitor input type smoothing circuit, dissatisfaction with the harmonic wave control standard to be provided as a revision of the IEC 555-2 standard will be a problem. Authors have therefore started development of a new SRM with reduced harmonic current. They have studied and evaluated several types of Power Factor Correction (PFC) circuits. In the Multi-SR system (MSR system) - newly developed computer power supply system -, as matters now stand, it has been judged that the feedback control type boost PFC used in this system is the optimum. Authors have therefore decided to adopt the feedback control type PFC in the new SRM under development.