Study of Frequency Modulated Boost Converter Operating in Discontinuous Conduction Mode

摘要

Switch-mode power converters (SMPC) are very popular today mainly because of higher efficiency and smaller size. They are used in switch-mode power supplies, battery chargers, active power factor correctors, etc [1-3]. SMPC can operate in both continuous and discontinuous conduction modes (CCM and DCM respectively). The main mode of operation is usually CCM, in which power inductor current never falls to zero. DCM sometimes is chosen to be the main mode of operation of SMPC, mainly, due to feedback loop stability considerations [4, 11, 12]. At light loads SMPC can also enter DCM. The main disadvantage of SMPC is high electromagnetic interference (EMI) [3, 5]. In recent years spread spectrum method which is usually based on the use of switching frequency modulation (FM) has been of great interest for EMI reduction [5, 6, 9]. However the use of this method can substantially increase output voltage ripples (OVR) in both CCM and DCM [5-9]. In [8] effect of FM on OVR of closed-loop buck converter operating in DCM was examined in details, however effect of FM on OVR of other SMPC topologies operating in DCM has not been investigated yet. In this paper OVR of FM boost converter operating in DCM will be considered and influence of modulation parameters on OVR will be examined. Experimental verification will also be performed.