Billings, chapters 2.17, “The DC-to-DC Transformer Concept,” and 2.20, “DC-to-DC Switching Regulators” John Griffin EE 136 Project December 2003 Professor Zhou/SJSUOutlineSlide 3Obsolete mechanically-switched DC-to-DC transformerSlide 5Modern DC-to-DC transformer: self-oscillating, square wave, push-pull converter with bi-phase rectificationDC transformerSquare wave transformer circuit analysis: half-cycle 1Square wave transformer circuit analysis: transitionSquare wave transformer circuit analysis: half-cycle 2Trying to simulate DC transformer…Slide 12…but for the full circuit Simplorer would not cooperate…and here.Slide 15Buck, boost, b-b, Cuk, w / current signalsWhich type of regulator to choose?Slide 18History of Cuk converterCuk converter operationSome Cuk converter applicationsSlide 22Ripple regulator purpose, actionFig. 2.20.5: Ripple Regulator in a buck converter (basic buck converter is below)Ripple regulator output voltage: magnitude and frequency can be varied by choice of components. Often around 40 mV peak-to-peak.Hysteretic control of ripple by regulatorRipple regulator simulationIdeal and simulated ripple reg. output voltageRelevant URLs / Billings 2.17 & 2.20Billings, chapters2.17, “The DC-to-DC Transformer Concept,”and 2.20,“DC-to-DC Switching Regulators”John GriffinEE 136 ProjectDecember 2003Professor Zhou/SJSUOutline•Chap. 2.17–Obsolete DC-to-DC transformer design–Modern transistor-switched DC-to-DC transformerChap. 2.20•Chapter 2.20–Switch mode families–Cuk converter–Ripple regulator•Relevant URLs•Chap. 2.17–Obsolete mechanically switched DC-to-DC transformer design–Modern transistor-switched DC-to-DC transformerChap. 2.20Obsolete mechanically-switched DC-to-DC transformer•Chap. 2.17–Obsolete mechanically switched DC-to-DC transformer design–Modern transistor-switched DC-to-DC transformerChap. 2.20Modern DC-to-DC transformer: self-oscillating, square wave, push-pull converter with bi-phase rectification–Advantages: simplicity, low cost, size–Disadvantages: inefficient; frequency varies depending on load & input voltageDC transformer•Frequency can change with input voltage and load changes, but with screening the electromagnetic interference (EMI) that results can be screened out•Circuit does not provide regulation, so normally a regulator circuit is added after this circuit’s outputSquare wave transformer circuit analysis: half-cycle 1Square wave transformer circuit analysis: transitionSquare wave transformer circuit analysis: half-cycle 2Trying to simulate DC transformer…•Simplest representation works fine…Trying to simulate DC transformer……partially built circuit works fine; output voltage trace was like that of simpler version……but for the full circuit Simplorer would not cooperate•Every try led to error, ‘out of memory’, etc., such as pictured here……and here.•Varying choices of component sizes could not overcome simulator hanging at its first attempt at transformer polarity change•Chap. 2.20–Switch mode families–Cuk converter–Ripple regulatorBuck, boost, b-b, Cuk, w / current signalsWhich type of regulator to choose?For good performance without needing detailed design: “For most applications, for up to about 100 W, go with the CCM [continuous current] flyback. Over 100 W, line-powered and isolated, use either the isolated Cuk topology or a half-bridge, controlled as a PFC [power factor corrector].” -- Dennis Feucht, power elect. Designer (article is in list of URLs)•Chap. 2.20–Switch mode families–Cuk converter–Ripple regulatorHistory of Cuk converter•Further work at Caltech, especially by Cuk in his PhD Thesis, produced a fourth member of the basic dc-to-dc switching regulators which has been described as an optimum topology because of its symmetrical structure and non-pulsating input and output currents. The new optimum topology dc-to-dc switching regulator is now commonly known as the Cuk converter after its inventor.Cuk converter operation"The Cuk converter is obtained by using the duality principle on the circuit of a buck – boost converter. Similar to the buck – boost, the Cuk provides a negative-polarity regulated output voltage with respect to the common terminal of the input voltage. The most important feature of this topology is the fact that a capacitor, instead of an inductor, is used as the primary means of storing and transferring energy from input to the output. This causes energy transfer to occur during both ON and OFF gated switch intervals. Operation is performed at almost zero ripple current at both the input and output of the circuit. These characteristics make the Cuk converter the closest to an ideal DC power supply of any topology.” -- "2001 Future Energy Challenge Final Report“, on inverter design project at UTEP (article in URL list)Some Cuk converter applications•Magnetic Recording Head Bias•Digital camera CCD bias•LCD bias•GaAs FET bias•Positive to negative conversion(Source: National Semiconductor LM2611A/B 1.4MHz Cuk Converter data sheet)•Chap. 2.20–Switch mode families–Cuk converter–Ripple regulatorRipple regulator purpose, action•Strictly limits output voltage ripple to “hysteresis” of op amp comparator•Tends to be used with buck converter more than with other types•Hysteresis ramp-up and ramp-down voltage are defined by inductor, output capacitor, supply voltage, load currentFig. 2.20.5: Ripple Regulator in a buck converter (basic buck converter is below)Ripple regulator output voltage: magnitude and frequency can be varied by choice of components. Often around 40 mV peak-to-peak.Hysteretic control of ripple by regulator•From Texas Instruments design guide for synchronous buck converters: “Although some may see the variable switching frequency of hysteretic control as a drawback, it is usually not a problem. Input voltage, output capacitor ESR, capacitor ESL, and output inductance have the most influence on switching frequency. If the input voltage is regulated within a relatively narrow range, and stable filter components are used, the frequency variation is small. Also, since the output voltage ripple is well controlled, this variation is rarely a problem for overall system operation. In addition to excellent output-voltage regulation and user-adjustable output-voltage ripple, the controller also provides user-adjustable soft-start and overload