Abstract
A new zero-voltage-switching (ZVS) control approachis presented for pulsewidth modulation (PWM) buck convertersunder discontinuous conduction mode (DCM)/continuousconduction mode (CCM) boundary. This proposed technique compensatesfor control circuit delay, and hence, turns on power MOSat the instant exactly when drain-to-source voltage becomes zero.No complicated timing calculation circuits or additional externalcomponents are required. This proposed integrated ZVS controlcan be applied to other dc–dc converters as well. The correspondingcircuit analysis, implementation, and die photograph are presentedin this paper. Simulation and experimental results for an examplecircuitwithVIN of 5VandVOUT of 3.3Vreveal that buck converterswith the presented ZVS technique have higher efficiency than conventionalones, especially at higher frequencies. At about 3.6 MHzoperation, the measured conversion efficiency of the PWM buckconverter under DCM/CCM boundary mode with the proposedZVS approach is 11% higher.Index Terms—Boundary mode, buck, pulsewidth modulation(PWM), soft switching, zero voltage switching (ZVS).
I. INTRODUCTION
RECENTLY, hand-held battery-powered systems, such asMP3 players, digital cameras (DSC), GPS systems, etc.,have become increasingly popular. Power supplies with smallsize, light weight, fast transient response, and high power densityare required for these mobile applications. These feasible propertiescan be achieved by increasing the switching frequency,but this may lead to higher switching loss and more electromagneticinterference (EMI) noise. To solve these problems, significantresearch effort has been devoted to zero-voltage-switching(ZVS) control techniques, such as quasi-resonant (QR) converters[1]–[7], phase-shift pulsewidthmodulation (PWM)[8]–[11],active clamp [12], [13], asymmetrical half bridge [14], [15], andsome other schemes [16]–[20].QR converters were first presented in the 1980s [4]–[7]. Thisconcept, compared with conventional PWM schemes, reducesswitching losses and noises at high operation frequency by replacingpower switches with resonant ones. QR converters caneasily achieve zero current switching (ZCS) or ZVS. Yet, additionalexternal components are required, and cost, size, andweight of the system may increase as well. This can be clearly seen in Fig. 1, which shows a conventionalPWMbuck converterand a ZVS QR buck converter. Furthermore, because of theirresonant behavior, power switches suffer from higher conductionloss and stress in QR converters than in conventional PWMconverters.In PWM buck converters under discontinuous conductionmode (DCM)/continuous conduction mode (CCM) boundary,power switches may be turned on at ZVS condition like thosein QR converters. Resonant components are not required, andvoltage stress of the power switch during its OFF time is just thesame as that in conventional PWM converters. However, thereare other advantages like fast dynamic response, high stability,easy design, simple control, low cost, etc. In a PWM bucksystem, the inductor L1 resonates with the combination of CS1(parasitic capacitance of power MOS S1) and CD1 (the junctioncapacitance of free-wheeling diode D1) when it runs outof its stored energy.


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