ECEN5817 Lecture 36Turn in HW9HW10 due in class on Monday, April 23. The one-week grace period for off-campus students expires 5pm MT on Monday, April 30ECEN 58171Two-transistor (synchronous rectifier) ZVS-QSW switch cellQDConverter examplesHigh-frequency view of the switch networkDQDDQDQBasic switch implementation optionsQ: current-bidirectional (e.g. MOSFET)D: singlequadrant (diode)D: single-quadrant (diode)Q: current-bidirectional (e.g. MOSFET)D: current-bidirectional synchronous rectifier (e.g. MOSFET)ECEN 58172QDTwo-transistor (synchronous-rectifier) ZVS-QSWD1+i1(t) i2(t)+LrL+I+–CrVgD2Q1+v2(t)v1(t)LCRV–––• Resonant transitions but transistor and conduction intervals are similar to PWM; peak voltages are the same as in hard-switched PWM • Tank capacitor is in parallel with all semiconductor devices, hence all semiconductors operate with ZVS•Peak currents are increased, and are similar to DCMPeak currents are increased, and are similar to DCM• Constant-frequency duty-cycle control, similar to standard PWM, is possibleZVSQSW ( tt iti ) t t d t b f th ECEN 58173•ZVS-QSW (resonant-transition) concept extends to a number of other important practical soft-switching converters2-transistor ZVS-QSW: state plane D1+i1(t) i2(t)+LrL+I+–CrVgD2Q1v2(t)–v1(t)–CRV–V1V1_ECEN 58174Waveforms and definition of duty cycle, 2 transistors• Here, the controller duty cycle Dcis defined as the duty cycle that would be yychosen by a conventional PWM chip•The resonant transitions areThe resonant transitions are “dead times” that occur at the beginning of the DTsand D’TsintervalssECEN 58175Constant-frequency control characteristicsof the 2-switch ZVS-QSWConstant frequency, duty cycle control:Low output impedance, µ doesn’t depend much on JV i il t ti l PWM CCM it h b t hibit ZVS ECEN 58176Very similar to conventional PWM CCM switch, but exhibits ZVS over a range of operating points2-switch ZVS-QSW: ZVS boundaryReducing F = fs/f0leads to ZVS over a wider range of µ and JECEN 58177AC (small-signal dynamic) modeling of quasi-resonant convertersQuasi-resonant converters inherit properties of PWM parents, with switch conversion ratio  playing the role of the PWM switch duty cycle dAC modeling approach:•Start from(vif) found for the resonant switchStart from (v,i,fs) found for the resonant switch• Perturb and linearize• Replace d with  in the small-signal AC dynamic model of the PWM parent converter (from ECEN5797 Intro to PE)ECEN 58178Example 1: Full-wave ZCS-QR BuckECEN 58179Small-signal AC model of the PWM buck converterTextbook, Fig.7.17(a)ECEN 581710Small-signal AC model of the full-wave ZCS-QR buck ECEN