Design (Block diagram/topology) of high-current (I>100 A) power supply - Page 1
Forum section: electronics / general

author: KenGrimes
author_rank: Newbie
timestamp: June 10, 2020, 01:22:00 pm
content: Hello everybody,I recently watched this videoabout the teardown of ahigh voltage(300 V) commercial power supply. I reckon that the block diagram (image attached) is essentially a bridge rectifier followed by a DC/DC convertor, which given the high voltage involved, is implemented with a phase-shifted resonant convertor that uses soft-switching to reduce switching loss.[ Specified attachment is not available ]I was wondering, how arehigh currentcommercial power supplies designed, let’s say DC current above 100 A such as thesehttps://www.keysight.com/de/de/products/dc-power-supplies/ate-system-power-supply/n5700-series-ate-system-power-supplies-750w-1500w.htmland thesehttps://www.us.lambda.tdk.com/products/programmable-power/genesys.htmlone.In theory, a bridge rectifier followed by a buck convertor would do the job, but I imagine it would be terribly inefficient (the same reason that the high-voltage supply isn’t implemented using a boost convertor). I tried to find a teardown of a high current power supply on the forum but to no avail.Does someone know topologies are used in commercially availablehigh currentpower supplies?Many thanks in advance!Cheers,Ken

author: dzseki
author_rank: Frequent Contributor
timestamp: June 10, 2020, 01:41:27 pm
content: Well, just last week I have starred above a gutted (and probably busted) 5V 120A TDK-Lambda power supply.By concept it looked like plain ordinary switching PSU, but the secondary side was on steroids. I'll snap a picture tomorrow as I've saved the secondary side, now I just describe:-The secondary winding was barely one turn on the transformer, and was made from a specially formed metal sheet.-Secondary rectification was done by simple schottky diodes (6pcs of dual 45A Schottky diodes TO-247 in parallel), here the rail was a solid metal bar again and the heat fin was the common connection point for these.-On the output there was a simple LC filter with a massive choke with only 3 turns (made of ~3x5mm size copper conductor) the capacitor bank was made of 6pcs of 4700uF capacitors in parallell.As I saw there was more mechanical virtue in the design than electrical, certainly more difficult to DIY.

author: KenGrimes
author_rank: Newbie
timestamp: June 10, 2020, 03:07:19 pm
content: Hi dzseki, thanks for your reply, that sounds really interesting, I would really appreciate if you upload some pictures. I'm very curious what kind of DC/DC convertor uses a secondary with only one turn.Cheers,KenQuote from: dzseki on June 10, 2020, 01:41:27 pm

author: Kleinstein
author_rank: Super Contributor
timestamp: June 10, 2020, 05:30:45 pm
content: It is not only the current that is important, but at first it is the power that matters. The low voltage, high current supply (e.g. CPU power in the PC) use a multi phase buck at the end and a more conventional isolated converter before that. At low voltages, high current synchronous rectification is a common.Another important factor is if one needs a variable output voltage. For a more or less fixed ratio a forward converter is preferred. The FPC stage may do some initial regulation too, and at higher power this may be required.

author: David Hess
author_rank: Super Contributor
timestamp: June 10, 2020, 07:17:01 pm
content: Quote from: KenGrimes on June 10, 2020, 01:22:00 pmA high frequency transformer is placed between the high voltage power switches and the buck output inductor. The transformer than steps the high voltage down (or up) to an appropriate level where the duty cycle is roughly 50% for the proper output.

author: dzseki
author_rank: Frequent Contributor
timestamp: June 11, 2020, 05:42:18 am
content: Here are two pictures as promised:

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 11, 2020, 07:31:23 am
content: About the only things different are:- Synchronous rectification is a big plus- If you're feeling clever, you can use a current doubler circuit. (This is a transform of the common full wave voltage doubler circuit, using inductors instead of capacitors, and swapping series for parallel branches.)- Switching impedances are so low that it can be difficult to impossible to manage parasitics. The solution is to use multiple stages in parallel.- Parallel stages can be phase-shifted (phase interleave) to reduce input and output ripple.A bunch of years ago, I had a client which wanted a high current supply for testing batteries. I made this:https://www.seventransistorlabs.com/Images/Racks.jpgEach board contains three 20A channels (synchronous rectified, necessary anyway to implement battery charge/discharge cycles), phased to reduce ripple current (though there's enough filtering to handle them being all in phase). Both boards in parallel do 120A. They'd probably be fine at 100A/board, given somewhat bigger components; I was very conservative on trace width. And as you can see, nothing special, wide open layout, no bus bars or brackets or anything, just screw terminals at the ends.If I were doing it over today, I think I'd go with more SMT, including the output transistors. Inductors probably SMT, bulk capacitors may still be THT, but few would be needed, and more ceramic and polymer capacitors would be used. Capacity might be about 20A/channel, maybe more. Multilayer board to improve routing, and electrical and thermal conductivity. Probably the board area can be reduced by 50-70% without much optimizing. Probably still needs heatsinks, which can be fitted, using thermal pads, taking heat off the top and bottom of components and board.Note this is low voltage input, it's just a buck converter; for offline operation, the secondary side looks much like this, but there's inverters supplying transformers on the primary side; and line filtering, aux supply and so on.As for type, a good old fashioned forward converter is fine, but resonant (LLC) can be done, with synchronous rectification, to improve efficiency. You might still be able to do phase interleave. (Good luck finding a controller, I think; it might need an MCU or FPGA -- i.e. a custom solution -- to pull off resonant phase interleave.)Tim

author: KenGrimes
author_rank: Newbie
timestamp: June 11, 2020, 11:32:59 am
content: Thanks a lot! Really interesting construction!Quote from: dzseki on June 11, 2020, 05:42:18 am

author: nali
author_rank: Frequent Contributor
timestamp: June 11, 2020, 12:18:00 pm
content: A long, long time ago when I was between jobs I worked as a contractor at Advance Power Supplies testing their 1500W Powermag SMPSUs. I can't recall much about them apart from they used custom ferrite cores with very tight B-H loops as magnetic switches for regulation.Unfortunately I can't find much about them now which is a shame as I wouldn't mind finding out more about how they worked (magnetics has always been a bit of a mystery for me). This was the beast in question, mainly 12V/125A and 5V/300A.http://www.farnell.com/datasheets/100779.pdfI do remember setting up the current foldback was fun as it involved a solid copper shorting bar which after a few seconds got HOT!

author: xavier60
author_rank: Super Contributor
timestamp: June 11, 2020, 12:56:01 pm
content: Quote from: nali on June 11, 2020, 12:18:00 pmMag Amps using saturable reactors are often used to independently regulate rails from the same SMPS transformer. Like the 3.3V from a PC power supply.I wonder how a Mag Amp is applied in a PSU with only one output rail.https://www.onsemi.com/site/pdf/inside_the_power_supply.pdf

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 11, 2020, 08:57:20 pm
content: Mag amps are mostly old fashioned, the most common exception being computer power supplies: the 3.3V rail is derived from the 5V secondary, with one phase being magamp regulated, hence allowing it to control over the 2.5-5V range. It's directly controlled by a TL431, which is why it's the most stable rail in the whole supply (typically within some mV, while the 5 and 12V rails vary by 10s of mV over load range), and which gives you some idea about how good the power gain is -- the TL431 can't exactly dissipate whole watts!Which, heh, they'll be moving away even from that pretty soon, won't they? All-12V PCs are due soon IIRC, with all the other supplies replaced with POL regulators. (Core and RAM have been POL for a very long time, and basically nothing has needed -5 or -12V for even longer; it's about time the 3.3 and 5V supplies go the same way. Alas, standards and compatibility!)There's old Unitrode (now TI) appnotes discussing magamp supplies, including single outputs -- the advantage is simple control, you only need a square wave oscillator on the primary side, possibly with current limiting. No PWM control whatsoever. Secondary side handles itself, one magamp and error amp per output. It made sense back in the days before PWM controller ICs -- you might need a dozen or more transistors, or op-amps and other analog glue, to implement such a function otherwise.There was no standard solution back then -- the 60s and 70s. No one was trying to sell chips, there wasn't nearly enough market to make one. SMPS would really only be called for on big supplies, such as for minicomputers, which weren't exactly mass market items. There were hacks, like the uA723 can be coerced into a switching regulator of sorts, the LM317 too even. Big iron supplies -- phase control SCRs and filter chokes -- were still very common!I once took apart a motor drive (VFD), contemporary (from the 70s). It used several beefy chokes, and a whack of SCRs, to control DC bus (active rectification) and drive the motor (SCR bridge with resonant commutation). Used two large panels of analog and RTL to control it all -- they had to do everything the hard way back then!Needless to say, with cheap, high performance MOSFETs, and smart single-chip controllers (and regulators) saturating the market, we have little need of either approach anymore.Tim

author: duak
author_rank: Super Contributor
timestamp: June 12, 2020, 03:05:55 am
content: Before reading the article at the link, what needed 5.2 V, 770 A in the mid 70s?One thing I remember from a video interview on the power supply design was that it also used the 30 degree phase shift of delta-wye transformers to reduce the voltage ripple from 6% by doubling the ripple frequency.https://www.edn.com/cray-1-super-computer-the-power-supply/I'll bet that IBM, Control Data, Univac et al used very similar power systems in their big iron in the 60s and 70s.

author: filssavi
author_rank: Frequent Contributor
timestamp: June 12, 2020, 05:34:00 am
content: Even in all but the cheapest ATX power supplies mag amps are going the way of the dodo, the vast majority of the one sold in the last 3 to 5 years are now using regular run of the mill dc/dc converters to generate 3.3 and 5 from the 12VThe reason being mostly efficiency, everything but the worst bottom of the barrel chinese crap is 80+ bronze, and many going much higher. I also suspect that designing a DC/DC in this day and age for a company is much easier than The mag amp a EEs that know what a multiphase buck converter is are in much more plentiful supply than those that know how to design a mag amp.With how the modern electronics supply chain is shaped I would not even be surprised if mag amps nowadays are also more expensive, due to the reduced volume (less economy of scale)

author: David Hess
author_rank: Super Contributor
timestamp: June 12, 2020, 01:21:17 pm
content: Quote from: T3sl4co1l on June 11, 2020, 08:57:20 pmExternal storage still requires +5 and +12 volts and sometimes +3.3 volts so I wonder how that will be handled.Quote from: filssavi on June 12, 2020, 05:34:00 amI suspect the major power supply manufacturers have plenty of economy of scale to keep magnetic amplifier designs viable. But with a move toward single rail power supplies, there will be no place for them.

author: filssavi
author_rank: Frequent Contributor
timestamp: June 12, 2020, 05:24:42 pm
content: Single rail is not going anywhere anytime soon, atx12VO is indeed a thing but most of the PSU manufacturers have no intention of getting on board, as it will only cause huge consumer confusion and market fragmentationIt has been lobbied for and will be used by the big OEMs (hp dell and lenovo), as they design both mono and PSU (or rather subcontract custom ones)Economy of scale is not gone yet but it won’t hold for much longer, anything 80€ and up will not have mag amps for efficiency reasons, that takes out a large chunk of an already fairly small market (enthusiast desktop pcs).Laptops don’t use them for obvious reasons, servers value efficiency even more than desktops, and cost is usually not a big issueThey are only used when end stuff where the design is probably a decade old If not more

author: ocset
author_rank: Super Contributor
timestamp: June 13, 2020, 05:26:16 pm
content: Here's some stuff on it.But yes, as said above, its often paralleling, and synchronous rectification which are the main techniques for high current.You can shove voltage output regulating power supplies in parallel and just current clamp each one, so that all power supplies are limited in the amount of current they can push out.

author: bsdphk
author_rank: Regular Contributor
timestamp: June 13, 2020, 05:58:49 pm
content: "Before reading the article at the link, what needed 5.2 V, 770 A in the mid 70s?"One example from the early 1980'ies:https://datamuseum.dk/wiki/Rational/R1000s400The PSU is rated 5V/1000A, the two orange "garden hoses" are litze welding cables.About half way down this page:https://datamuseum.dk/wiki/Rational/R1000s400/LogbookYou will find pictures of the PSU after it blew up.We suspect somebody swapped the PSU without cleaning the busbars, and the extra resistance (1mOhm * 1000A = 1V!) overloaded the PSU.

author: ejeffrey
author_rank: Super Contributor
timestamp: June 22, 2020, 04:50:43 pm
content: Quote from: David Hess on June 12, 2020, 01:21:17 pmFor the big OEMs? They won't handle it, they will just ship only with M.2 form factor SSDs. For the high end, I imagine the solution will be hot-plug backplanes with built in PoL regulators. For power users and DIYers that need a handful of SATA drives I think the plan is to have SATA power outlets on the motherboard. This is not terrible as the power demands are not high and the motherboard will already need to have fairly beefy internal 5V supplies for USB indefinitely. Theoretically there could be an SATA 12V standard (ideally in a combined power+data cable), but I kind of doubt it given that these days even 1 SATA drive is the exception rather than the rule. By the time ATX12VO becomes common in the consumer space that will only be less frequent.

author: DannyTheGhost
author_rank: Contributor
timestamp: June 22, 2020, 06:09:46 pm
content: One of examples of such high-current PSUs would be the one I made last year as my first dive into the world of power electronics. This was 0-12V 0-100A PSU with CC/CV function and was made for usage in electrolysis setup for simple tasks.It was a fusion of modern and old technologies and layouts. It consists of PFC(dual interleaved boost topology) and PSFB topology with synchronous rectification on the output. Output is configurable just via MCU with LCDFully assembled transformer (with double winding CT secondary) with synchronous rectifiers (6xIRF3205 per tap), output inductor and output filtering:Fully assembled PSU in its casingNow, looking back at it, I still don't understand how it still works without any problems and even with good regulation

author: KenGrimes
author_rank: Newbie
timestamp: June 23, 2020, 09:50:06 am
content: Looks very nice, thanks for sharing.How did you manage to solder those white cables to those aluminium heat sinks?Quote from: DannyTheGhost on June 22, 2020, 06:09:46 pm

author: DannyTheGhost
author_rank: Contributor
timestamp: June 23, 2020, 04:03:02 pm
content: Quote from: KenGrimes on June 23, 2020, 09:50:06 amI didn't.Those heatsinks are cooling down these IRF3205x6 transistors each. There is 12 transistors total and at full power (during 12V 100A) they dissipate almost 35W. If I wouldn't have used these transistors for synchronous rectification and used diodes instead of them - this number would be more than 100W, and cooling this amount of heat would have been quite the challenge for me.