toroidal core for high current
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From: Jenkins on 19 Jul 2010 04:53 How physically large does a toroidal core need to be to handle a 100A smps buck or flyback configuration? I used http://www.daycounter.com/Calculators/Switching-Converter-Calculator2.phtml to calculate the inductance, Volts In 250 V Volts Out 25 V Load Current 100 A Freq. 50000 KHz Vripple 0.25 V Duty Cycle 10 % Ipp Inductor 5 A Ipk Inductor 102.5 A Irms 97.510683175401 A L 0.09 uH C 0.8 uF which seems awful small? For a toroid, L = u*(rN)^2/D, and I played around with different sizes and giving me relatively large inductance's(much larger than 0.1uH). steel core, r = 1cm, D = 5cm, N = 20, L = 700uH. It seems that the inductance is pretty low for large currents, Load Current 1 A Vripple 0.25 V Duty Cycle 10 % Ipp Inductor 0.001 A Ipk Inductor 1.0005 A Irms 0.99950004168751 A L 450 uH C 0.008 uF So it should be relatively easy to get an inductor for doing 100A's for a buck converter? Even an air core would work? If the calculations above are correct what are the real issued involved for high current inductors used in smps? Core saturation[how to calculate?]? Heat dissipation[Need thick wires => physically large inductor]? High frequency issues? Can one buy off the shelf inductors that can handle 100A+ or would they be difficult to obtain the core material?
From: Tim Williams on 19 Jul 2010 09:34 "Jenkins" <phreon111(a)gmail.com> wrote in message news:45a92d0d-d2a1-451f-93f3-62c9bee710c9(a)q22g2000yqm.googlegroups.com... > How physically large does a toroidal core need to be to handle a 100A > smps buck or flyback configuration? > > I used http://www.daycounter.com/Calculators/Switching-Converter-Calculator2.phtml > to calculate the inductance, Surely you meant http://www.daycounter.com/Calculators/Switching-Converter-Calculator.phtml ? The above page says "division by zero" and doesn't have active fields. In fact, it requires POSTDATA to function. > Volts In 250 V > Volts Out 25 V Awfully large ratio. Why not forward converter? > Load Current 100 A > Freq. 50000 KHz 50MHz? > Vripple 0.25 V > Duty Cycle 10 % > Ipp Inductor 5 A > Ipk Inductor 102.5 A > Irms 97.510683175401 A > L 0.09 uH About five inches of microstrip. Sounds reasonable. Give this a try: http://schmidt-walter.eit.h-da.de/smps_e/smps_e.html I prefer half bridge PP. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Hammy on 19 Jul 2010 10:17 >"Jenkins" <phreon111(a)gmail.com> wrote in message news:45a92d0d-d2a1-451f-93f3-62c9bee710c9(a)q22g2000yqm.googlegroups.com... >> How physically large does a toroidal core need to be to handle a 100A >> smps buck or flyback configuration? >> >> I used http://www.daycounter.com/Calculators/Switching-Converter-Calculator2.phtml >> to calculate the inductance, > Either one of those topologies isn't the best choice. A flyback at 2.5kW would be ridiculous. >> Volts In 250 V >> Volts Out 25 V As Tim suggested you might want to look at a topology that uses a transformer. Half or full bridge. You also will probably need PFC on the front end if you plan on getting that power out of a European residential line.You will be needing capacitor's with an "S" for handling the large rms currents and large beefy semi's with an "S" and brick heat sinks fans etc. >> Load Current 100 A >> Freq. 50000 KHz You aren't going to be banging around FET 'S or IGBT's that you are going to be needing at 50 MHz and no controller I know of operates at 50MHz. For such a large output current you may also want to look into interleaving or dual/triple phase controllers. > >> Vripple 0.25 V >> Duty Cycle 10 % >> Ipp Inductor 5 A >> Ipk Inductor 102.5 A >> Irms 97.510683175401 A >> L 0.09 uH > >About five inches of microstrip. Sounds reasonable. ;-) >Give this a try: >http://schmidt-walter.eit.h-da.de/smps_e/smps_e.html >I prefer half bridge PP. > >Tim
From: Tim Wescott on 19 Jul 2010 13:12 On 07/19/2010 01:53 AM, Jenkins wrote: > How physically large does a toroidal core need to be to handle a 100A > smps buck or flyback configuration? > > I used http://www.daycounter.com/Calculators/Switching-Converter-Calculator2.phtml > to calculate the inductance, > > Volts In 250 V > Volts Out 25 V > Load Current 100 A > Freq. 50000 KHz > Vripple 0.25 V > Duty Cycle 10 % > Ipp Inductor 5 A > Ipk Inductor 102.5 A > Irms 97.510683175401 A > L 0.09 uH > C 0.8 uF > > which seems awful small? For a toroid, L = u*(rN)^2/D, and I played > around with different sizes and giving me relatively large > inductance's(much larger than 0.1uH). > > steel core, r = 1cm, D = 5cm, N = 20, L = 700uH. > > It seems that the inductance is pretty low for large currents, > > Load Current 1 A > Vripple 0.25 V > Duty Cycle 10 % > Ipp Inductor 0.001 A > Ipk Inductor 1.0005 A > Irms 0.99950004168751 A > L 450 uH > C 0.008 uF > > So it should be relatively easy to get an inductor for doing 100A's > for a buck converter? I would expect that at 100 amps you're going to start getting into issues not just of core materials, but of wire heating and possibly even mechanical vibration induced by magnetic effects. > Even an air core would work? I don't think so. An air core inductor would either have so much parasitic capacitance that your switching losses would go through the roof, or it would radiate enough to seriously impact your efficiency (and to interest the FCC). > If the calculations above are correct what are the real issued > involved for high current inductors used in smps? But the numbers are absurd. > Core saturation[how to calculate?]? See if you can find the "Amidon Associates" website -- they used to peddle a book that went into that, and they had a core saturation calculator. It can be done, and the better ferrite manufacturers publish the data. > Heat dissipation [Need thick wires => physically large > inductor]? The core also heats directly, from both conduction losses (if it's one of the really low frequency ferrites) and from hysteresis losses. > High frequency issues? Now you ask!! > Can one buy off the shelf inductors that can handle 100A+ or would > they be difficult to obtain the core material? Have you looked in the DigiKey catalog? I don't think there are inductors going up that high, but you can obtain semi-custom magnetics if you can find the names of the right transformer companies. Suspect websites* and ridiculous numbers (50MHz?) aside, you've just asked a question akin to "I'm going to make potato salad for a party this weekend -- how big of a bowl do I need?". The amount of energy that the core stores each cycle depends inversely on the frequency of operation of the circuit. The losses in the core are more complex, but also depend both directly and as the square of the inverse of the frequency. In general, as the circuit frequencies get higher the potential core losses go down**, but the switching losses in the transistors go up. The art of switching supply design for as long as I've been around to watch has advanced by finding transistors and circuits that allow faster and faster switching speeds, allowing the magnetics (and thus the whole circuit) to get ever smaller. But 50MHz is a bit high for a realistic circuit. * _Any_ website that purports to design a switcher for you is suspect -- even the ones by the semiconductor companies. ** Depending on the core material. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
From: Jenkins on 19 Jul 2010 13:21
On Jul 19, 8:34 am, "Tim Williams" <tmoran...(a)charter.net> wrote: > "Jenkins" <phreon...(a)gmail.com> wrote in messagenews:45a92d0d-d2a1-451f-93f3-62c9bee710c9(a)q22g2000yqm.googlegroups.com... > > How physically large does a toroidal core need to be to handle a 100A > > smps buck or flyback configuration? > > > I usedhttp://www.daycounter.com/Calculators/Switching-Converter-Calculator2... > > to calculate the inductance, > > Surely you meanthttp://www.daycounter.com/Calculators/Switching-Converter-Calculator.... > ? > > The above page says "division by zero" and doesn't have active fields. In fact, it requires POSTDATA to function. > > > Volts In 250 V > > Volts Out 25 V > > Awfully large ratio. Why not forward converter? > > > Load Current 100 A > > Freq. 50000 KHz > > 50MHz? > > > Vripple 0.25 V > > Duty Cycle 10 % > > Ipp Inductor 5 A > > Ipk Inductor 102.5 A > > Irms 97.510683175401 A > > L 0.09 uH > > About five inches of microstrip. Sounds reasonable. > > Give this a try:http://schmidt-walter.eit.h-da.de/smps_e/smps_e.html > I prefer half bridge PP. > > Tim > > -- > Deep Friar: a very philosophical monk. > Website:http://webpages.charter.net/dawill/tmoranwms That should be 50khz and not 50Mhz. L = 450uH... still seems relatively small. |