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EE467-567'10_lect13-Fnl

# EE467-567'10_lect13-Fnl - EE 467/567 INTEGRATED POWER...

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EE467/567 Integrated Power © 2010, D. C. Hopkins EE 467/567 -- INTEGRATED POWER EE 467/567 -- INTEGRATED POWER ELECTRONICS ELECTRONICS Dr. Douglas C. Hopkins Dept. of Electrical Engineering University at Buffalo EE467/567 Integrated Power © 2010, D. C. Hopkins Voltage Multipliers Voltage Multipliers

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EE467/567 Integrated Power © 2010, D. C. Hopkins One More Circuit One More Circuit The Cockcroft-Walton circuit is used to create VERY high voltages More appropriate for very low load currents Operates from an alternating source using parallel to series connections. Capacitors and passive diodes appear in pairs A big advantage is that the device ratings can be modest: reach 100 kV output with 1 kV devices in a long string. The output voltage is half the number of capacitors times input peak voltage, less the diode drops, V out = V in pk (n/2) , where n is no. of caps The output capacitance is a series combination of n/2 parts. C cw C cw C cw C cw C cw C cw + V cut - V in EE467/567 Integrated Power © 2010, D. C. Hopkins One More Circuit One More Circuit +HOMEWORK +HOMEWORK Charge capacity based on 10% voltage drop is therefore about I = fC(0.1)V(n/2) . HOMEWORK - 5.9, page 202
EE467/567 Integrated Power © 2010, D. C. Hopkins End - Capacitance End - Capacitance Converters Converters EE467/567 Integrated Power © 2010, D. C. Hopkins New topic - New topic - Discontinuous Mode of Discontinuous Mode of Operation Operation We have taken advantage of large L and large C to form near-ideal sources and loads. In these cases, KVL and KCL make the switch action definite and pre-determined.

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© 2010, D. C. Hopkins How Large? How Large? When is L large enough? So far, we have some time constant arguments. The time constant should be much larger than the period, L/R = t >> T. Similar arguments for C. There are times when no KCL current path is necessary. In dc-dc converters, light loads imply no upper limits on L. EE467/567 Integrated Power © 2010, D. C. Hopkins V out = D 1 V in What if the load is disconnected? What if inductor energy or capacitor energy reaches zero at some point during a cycle? If inductor current drops to zero, no current path is needed (KCL). The path is discontinuous, and the converter is in discontinuous mode. In discontinuous mode, the KVL and KCL constraints change. We can have intervals with all switches off or all on without violations. With diodes, this behavior is automatic. Buck Converter
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EE467-567'10_lect13-Fnl - EE 467/567 INTEGRATED POWER...

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