Help understanding of SMPS transformer characteristics  - Page 1
Forum section: electronics / beginners

author: sahko123
author_rank: Frequent Contributor
timestamp: April 13, 2022, 02:40:30 pm
content: Designing a linear supply is probably the easiest thing in the world. SMPS's are aids.ATM I'm trying to figure out what type of topology I need for my supply. The supply is a 120-150W (24V @ roughly 5A). I'm thinking of going with either Forward topology or push-pull/half bridge. Mainly I'm trying to understand the parameters to look for in a transformer. Either I'm not looking in the right places or there seems to be a lack of reasonable +100W transformers for small smps designs. My criteria was simply to not have a large clunking transformer.I've found one transformer on digikey (https://www.we-online.com/katalog/datasheet/750811351.pdf). I just need help understanding it's capabilities and parameters. The saturation current is listed at 7.4A for I assume the primary, how would this relate to the maximum power I can get through the transformer? I will be using rectified mains so there will be a potential of ~340Vdc at most on the primary. Are there also any good resources on understanding of SMPS transformer parameters and characteristics? Also on the datasheet that Wurth provides on the secondary it says 36V@3A. Does this mean that each tap is capable of this voltage and current? Or that this is the capability when all the taps are paralleled?Thanks for any and all responses!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 13, 2022, 05:19:32 pm
content: Don't. There are enough EMC and safety concerns that you are far, far better off using an off-the-shelf supply from a reputable, middling level manufacturer -- XP Power, Murata, MeanWell, etc.For learning purposes, you can do everything at low voltages, and scale up in voltage, current, frequency, vary the topology, etc., without danger of touching mains voltage, blowing up buckets of power transistors, etc. The controls are the same for any given topology, and the inverter switching dynamics pop up gradually with increasing size / frequency, or can be modeled with some added parts.Tim

author: Terry Bites
author_rank: Super Contributor
timestamp: April 13, 2022, 07:01:25 pm
content: Looking at the datasheet, its shows an expected operating frequency of 66KHz, an input voltage in the 120-375V range andan output power of only 2.4VA. Its not a lot to go on and the power output is way too low for your application.As Tim says- Don't. Any ready made unit will cost far less than any DIY design and come with safety approvals, EMC complinance and such.I always go for the enclosed types. Its one less thing in your project trying to kill you.They are not hard to find eghttps://www.ebay.co.uk/sch/i.html?_from=R40&_sacat=0&_nkw=24+v5+a+power+supply&_blrs=spell_checkwww.amazon.co.uk/1pcs-Switching-Power-Supply-110V/dp/B09LSDWTGH/ref=sr_1_4?crid=3DV6U7VXDAEDE&keywords=AC+110V%2F220V+to+DC+24V+5A&qid=1649875954&sprefix=ac+110v%2F220v+to+dc+24v+5a%2Caps%2C174&sr=8-4Can you be tempted by a cpc.farnell.com/tt-electronics/srs-100-24/ac-dc-100watt-24vdc-4-5a-enclosed/dp/PW04304?st=100w%20power%20suppliesor.....

author: sahko123
author_rank: Frequent Contributor
timestamp: April 13, 2022, 08:09:17 pm
content: I get it would be easier and safer to buy an off the shelf power supply but the reason I'm trying to design one is to learn how to do so. If at some point I give up on designing one I will simply buy an off the shelf one (but end up learning very little to nothing). I have no issue with working at high voltages and have worked at higher voltages before.The plan is to put together a design, prototype it, abuse and test and qualify it for the task, if it fails either fix whatever issue arose or if its inherently broken ditch it and buy an off the shelf one. At least this way I learn from my mistakes. The whole project is a learning experience after all.Where did you get 2.5va from? I can't find any mention of that anywhere on the datasheet.

author: strawberry
author_rank: Super Contributor
timestamp: April 13, 2022, 08:36:02 pm
content: 50..100W incandescent light bulb / or equivalent resistordont touch wires/metal with handsdead time(prevent two transistors conducting at the same time)2switch forward would be better for beginnerfollow instructionshttps://danyk.cz/svar_en.htmland have funinvest in insulation transformer, if it is still fun and want to probe with oscilloscope

author: TimNJ
author_rank: Super Contributor
timestamp: April 13, 2022, 08:38:08 pm
content: It's commendable to try a new thing. Just like any sub-discipline, there is a lot to learn, and certainly a lot you "don't know that you don't know". I think the warnings given above may be (mainly) from a point of safety. For linear supplies, aside from correctly wiring a mains fuse and dealing with mains wiring, you are relatively safe once you are on the secondary side of the transformer. Given you are using an off-the-shelf 50/60Hz transformer (made by a reputable manufacturer) you are protected by the expertise of the transformer manufacturer.For AC-input switch-mode supplies, you usually don't have the built-in safe guard of a transformer. So, to safely work on SMPS, you often need to re-think your workbench to make this a relatively safe endeavor. (isolation transformer, differential probes, etc.)...plus training yourself on how to work around high-ish voltages safely.It's all doable! But if you are not aware of the potential dangers, you need to start there first.In terms of technical design, of course, that is a rabbit hole too if you've never done it before. I now have about 5 years SMPS design experience, and it took me at least 2 years before being able to design anything on my own. There is a lot to be learned about how to design ~safely~. This includes PCB layout (spacing), acceptable methods for transformer construction, and proper selection of components close to the mains input. Off-the-shelf power supplies are certified to a variety of safety standards which check compliance of the aforementioned...Plus there is EMC, but that's a whole different story.I certainly do not want to "gatekeep". It's not impossible by any stretch, and I think you should give it a shot if it really interests you.For this power range, the present-day industry solution is Transition Mode (TM) PFC + LLC resonant. In the past, the topologies you listed were more common. They *may* be more simple in some sense (easier to wrap your head around?), but if you are starting from basics, maybe forget the old stuff and try the new stuff.This NXP chipset is extremely popular in the industry. There is a demo-board available. It is expensive, but for a newcomer, it may be a better use of your time to start with something that already works and/or can reference later if you choose to design your own from scratch.https://www.nxp.com/products/power-management/ac-dc-solutions/ac-dc-controllers-with-integrated-pfc/240w-computing-power-supply:TEA1916DB1262

author: sahko123
author_rank: Frequent Contributor
timestamp: April 13, 2022, 08:39:02 pm
content: I understand how to work with mains my issue is trying to understand transformer charecteristics not how to make a welder

author: sahko123
author_rank: Frequent Contributor
timestamp: April 13, 2022, 08:48:14 pm
content: It's all part of the learning experience at first. I'm very much aware that I don't know Jack about how to make these supplies besides their lime absolute most basic operating principle. So for now I'm trying to build up the basic technical knowledge such as how to choose a transformer.The safety aspects are a constant concern but that's what comes with working on mains. Especially when it comes to correct measuring and isolation.Guven your knowledge could you explain some of the parameters in the datasheet? Things like winding resistance and ratios are self explanatory but is there a way to 'get' things like power/current capabilities/limits from at least this datasheet? Or is it something thats so dependant on the driving circuitry (say in terms of frequency) that it's impossible to say with certainty?

author: bdunham7
author_rank: Super Contributor
timestamp: April 13, 2022, 08:49:27 pm
content: I'm not an SMPS design expert, but I do fix them and I've seen that a lot of them in your power and voltage range are simply flybacks and they work fairly well in most cases--the issues they have are caused by parts thrifting, running everything at or beyond design maximums and stuffing it all in a small sealed box. The transformer you linked is listed as intended for an offline flyback design. The total power is 108W, so I'd presume that is 36V@1A for each winding, since the windings are all identical.Perhaps you can just look for an appropriate transformer that is listed as being designed for use with a particular controller. If you go to this page, Wurth has listed their transformer lines by the type of controller they are designed to go with. Calculating and simulating all of this out using the transformers stated characteristics would be much more work, certainly beyond what I have the ability to do.Are you not going to have a PFC stage?

author: sahko123
author_rank: Frequent Contributor
timestamp: April 13, 2022, 09:00:45 pm
content: Yeah I'll most likely include a pfc circuit since I want the supply to be more or less efficient (at least given my lack of experience).I assume you got the power rating from the wurth website right? I also want to try and use either an ADI/Maxim/LT part (cause this way I have more of an excuse to put it on somebody else's dime) if possible but if it ends up being more effort than it's worth then I'll find another solution. I haven't seen too many transformers available from distributors directly that cater to ADI parts (probably because of less wide spread adoption). But as always I'm trying to keep my options open.

author: strawberry
author_rank: Super Contributor
timestamp: April 13, 2022, 09:59:48 pm
content: PFC wont make SMPS more efficient but increase power factor from ~60 to 95flayback is not transformer but coupled inductor

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 13, 2022, 11:55:42 pm
content: The other thing PFC is good for, is increasing power capacity: say you want over 800W from a 120V 15A circuit, can't do it without PFC. Less of a problem in .eu with 240V, though if you're on like a 7A circuit it's the same problem.As for transformers, consider this equivalent circuit:Apply some voltage to the left side, and it shows up on the right. If the transformer is 1:1 and ideal, then T1 can be removed and it's basically a straight pass-through. But there's still stuff around it. The shunt capacitors and series inductors make a lowpass filter (well, give or take the Cisos, but ignoring them for now).Physically speaking, a transformer at its most basic is e.g. a twisted pair wrapped around a core. You power one side and the other side mirrors it. Well, a twisted pair is a transmission line, with electrical length and impedance, and this sets a bandwidth limit. Indeed we can derive the L and C elements from a transmission line very easily.In fact, the standard cartoon of wires on opposite sides of a core, is one of the worst possible ways of making a transformer -- even with a very high permeability core, the amount of shared flux between windings is not all that great. And any missing flux manifests as series inductance, LLp and LLs (which, again, if we simplify T1 out, just add in series; we might use just one to express the secondary-shorted (primary-referred) (or vice-versa) total leakage inductance, when it's much smaller than the magnetizing inductance, anyway). So the more ideal case of a transformer is with the windings, as much as possible, in exactly the same places. This maximizes shared flux, minimizing LL, and maximizing bandwidth.The second most common representation, is how they're commonly built: blocks of windings either side-by-side, or layered on top, wound on a bobbin or toroid. This is problematic because, when sections consist of multiple layers -- the layers furthest from each other, see the least flux in common: that is to say, leakage is higher and bandwidth is lower.I won't go into much detail as far as network / filter theory, but suffice it to say: for a bandpass filter like this (when T1 is nonideal, its magnetizing inductance acts against source resistance, setting an LF cutoff; Cp-LL-Cs set the HF cutoff), impedance mismatch worsens bandwidth. Note that sqrt(L/C) has units of impedance, so we can compare source/load resistance to this and get some idea of matching.Finally, note that SMPS are typically quite poorly matched to begin with. This isn't a problem by itself -- just that it's a continuum that you want to be on the better side of. Namely, SMPS generally need quite low impedances, for example a 24V 10A power supply will have on the order of 24V/10A = 2.4 ohms in its switching loop. It is very difficult (read: tedious) to make transformers that low. But not much bandwidth is required, either: say Fsw ~ 100kHz, and we want to pass harmonics over 10MHz (for t_r < 50ns), well if we use a transformer with an electrical length corresponding to say 50MHz, and we have a mismatch factor of 5, we'll still get all the harmonics we wanted, and can add snubbers to dampen the rest; very little power indeed is present above the 100th harmonic, so this has little effect on overall efficiency.This is probably a whirlwind of statements and poorly-connected facts; I strongly encourage you to set up some models or simulations and play around with it. Wind some transformers yourself; plain old hookup wire will do nicely (most twisted pair is in the 100 ohm range -- transmission line impedance depends on ratio of conductor diameter to spacing, with insulation (dielectric constant) as a minor factor). Test the open, impedance-matched and short-circuit conditions, with whatever signals you have available -- something faster (sharper) than a 555 will do for square waves, or a function generator over 10MHz say, should do well enough in general. Try source/load/both termination conditions, see what that does to bandwidth. See if you can figure out the characteristic impedance, especially of really weird / bad geometries, like common mode chokes (transformers with side-by-side windings).Speaking of transformers -- a useful distinction is, what's an inductor and what's a transformer? Mind, what we traditionally call these things is whatever -- common mode chokes are used to choke a, well, a common-mode AC current; transformers are used to transform (converting power ~instantaneously between different voltage/current ratios), but we also call flyback transformers "transformers" even though they don't transform (power isn't converted instantaneously, rather energy is stored momentarily, then released!). Generally if it has multiple windings, it's safe to call it a "transformer", but it's useful to remember what kind it is.So, to make a useful distinction, you might note that a "flyback transformer" is better called a "coupled inductor", as we use inductors to store energy. Whereas a transformer ideally stores no energy (infinite magnetizing inductance), merely transforming instantaneous power (applied voltage/current).But also, on a more theoretical note, "transformer" captures the whole gamut, as a "non-ideal transformer" includes not just magnetizing inductance but leakage as well (making LLp and LLs redundant in the above). Usually expressing it as mutual inductance M, or coupling factor k (k = \$\frac{\left| M \right|}{\sqrt{L_p L_s}}\$), but leakage is also there (leakage being most useful for k --> 1, which is the usual case for "good" transformers).https://en.wikipedia.org/wiki/Leakage_inductanceThere are, of course, applications for k << 1, such as resonant SMPS, wireless power transmission, and RF tuned circuits, but these are likely beyond scope so this is a good point to stop.Tim

author: strawberry
author_rank: Super Contributor
timestamp: April 14, 2022, 08:13:08 am
content: winding technique will determine transformer performance and its parasitic inductance and capacitancediode and transistor switching loops will oscillate with transformer fun parasiticsPush-Pull need proper deadtime timing but it is low voltagein picture simple unregulated Push-Pull transformer SMPS

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 14, 2022, 01:08:04 pm
content: Oh weird, desat protection / Rds(on) current sensing? Haven't seen that on a 494 before.Tim

author: TimNJ
author_rank: Super Contributor
timestamp: April 14, 2022, 04:56:33 pm
content: For off-line AC/DC power supplies, very rarely are off-the-shelf transformers used. Wurth and others make a few, but they are usually designed around particular ICs and/or designed for particular reference designs. There are not so many "general purpose" SMPS transformers, which is maybe the idea you are missing?There are a lot less variables involved in specifying a mains frequency (50/60Hz) transformer. Fixed input/output voltage ratio, frequency is always the same, etc. So, it's much easier for a manufacturer to specify a VA rating because the input/output conditions are well controlled.For an SMPS transformer to be given an equivalent power rating, it would need to include a whole list of operating conditions for that power rating to remain true. Would need to include topology, switching frequency, and others.So, SMPS transformers are usually not thought about in terms of power rating, but usually more in terms of their losses at a given set of operating conditions. Based on the cooling solution, you can determine whether the amount of loss is acceptable (Can you get rid of the heat?). If not, adjust the transformer or the circuit to make it work.

author: sahko123
author_rank: Frequent Contributor
timestamp: April 14, 2022, 05:49:28 pm
content: This basically confirms my fear that 'designing' an offline smps is impractical. Since in the end you will most likely just create/copy an existing design. Basically the only reason at this point to continue on the path of creating a custom one is to try get it as compact as possible so far I've been able to find this combo for transformer/controller and even then I'm not sure if they are useable together in any capacity.https://www.digikey.ie/en/products/detail/w%C3%BCrth-elektronik/760895441/4692725and,https://www.digikey.ie/en/products/detail/onsemi/NCP1342BMDCDD1R2G/15218555Maybe they'll work together? maybe they'll die together? But maybe they won't even turn on be together or otherwise.Or possibly by some miracle they'll spring to life and happily generate 24V at whatever current the transformer lets through in the end. At this point I might just order the parts for it along with a pre-built and actually somewhat well designed power supply. Then assemble my one just to see if it works and then torture it a little to see if I can get it to choke within reason and if it turns out to work well at the small size I want. At this point I don't even know why its so difficult to create an offline supply without essentially having to go to a magnetics company to make a custom transformer.

author: TimNJ
author_rank: Super Contributor
timestamp: April 14, 2022, 06:15:35 pm
content: The transformer you linked is intended for LLC resonant topology. It is a split bobbin style with intentionally high leakage inductance. The controller you list is for quasi-resonant flyback. One of the key criteria for flyback islowleakage inductance. Basically: not compatible.If you insist on off-the-shelf transformer, yes, you'll pretty much be locked down to an existing reference design.I think you are jumping way ahead without really understanding much of the basics, and I don't think that will turn out well for you. I will reiterate that for switch-mode application it's generally more complicated than *voltage in - transformation by turns ratio - voltage out*. Some "transformers" are not even transformers at all (i.e. for flyback).Many of the IC manufacturers have design sheets that make it relatively easy to determine (ballpark) transformer parameters to achieve whatever you want. And if they don't have a plug-and-play spreadsheet available, well then you can certainly learn the fundamentals from scratch. Try that first, determine what transformer parameters youactuallyneed (# of turns, turns ratio, magnetizing inductance, leakage inductance, winding resistance, #of aux winding turns, and so on.).Thencheck if anything is available off-the-shelf. If not, you can tweak your design to make it work with something that exists. And, if not, you can always wind it yourself!

author: TimNJ
author_rank: Super Contributor
timestamp: April 14, 2022, 06:34:09 pm
content: Quote from: TimNJ on April 14, 2022, 04:56:33 pmJust want to make a little correction here. Output conditions of a line frequency transformer are not necessarily well controlled in the real world. Highly capacitive loads or other loads which distort the current waveform (away from an ideal sinusoid) will affect the maximum power rating of the transformer. Poor power factor loads require transformer derating by some factor.So like any component, a line frequency transformer is also specified at a particular set of conditions. Usage outside these conditions requires additional consideration.But my point still holds that specifying a small line frequency transformer for your project is generally much less involved than figuring out SMPS transformer parameters.

author: bdunham7
author_rank: Super Contributor
timestamp: April 14, 2022, 06:52:30 pm
content: Quote from: sahko123 on April 14, 2022, 05:49:28 pmYes, since you are probably not going to improve upon COTS SMPS controller chips with either a discrete design or your own custom ASIC, you'll always end up with a tweaked (or fubared) version of the reference design of whatever controller you are using. You can still optimize it for physical form and for quality by derating or 'unthrifting' it if you like. But you'll never compete with a complete COTS PSU--I recently bought a discounted 3D printer for $99 that comes with a brand name (Meanwell) 24VDC 350W PSU. I'm pretty sure I couldn't build that PSU for that price even with free labor.Here's some reading about resonant converters that might use the transformer you have linked. You can jump down to p.21 for a schematic if the math is too much at first.https://www.ti.com/seclit/ml/slup263/slup263.pdf

author: sahko123
author_rank: Frequent Contributor
timestamp: April 14, 2022, 08:48:49 pm
content: Ooooof. I incorrectly posted the llc transformer I meant to post this flyback transformer.https://ie.farnell.com/myrra/74060/transformer-etd39-120w/dp/1777987Id be happy if I could pull 100 Watts but probably even that would be a challenge. Would this be compatible with the flyback controller? Probably not the right use of words but essentially I'm asking if I should have a fire extinguisher handy. (I'll be using an external mosfet it's the transformer I'm worried about) the mosfet will probably just be 500v 6a capable with low rds on so I can reuse it as the pwm controller for the soldering iron

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 14, 2022, 08:52:20 pm
content: Quote from: sahko123 on April 14, 2022, 05:49:28 pmRight! Mass market products are optimized on cost; obviously you're not going to beat them with design costs included, and they'll be nestled right into the sweet spot of efficiency, cost, size and other specs that the market finds agreeable; anything else you do is likely adding more, or more expensive, components, or increasing EMI, etc.So there can still be some advantage, when those combinations of specs are just a bit too far from the application -- but you still need quite some justification for it, as designing a custom power supply still takes on the order of $10-20k professional engineering time, plus lab time to prove it's not blowing out EMI, plus safety review (UL etc.) because it's connected to the line. There are many applications that aren't perfectly served by commercial offerings -- say you need an oddball voltage that's just out of reach of the standard e.g. 24, 36, 48V, etc. types -- but you're almost always better off designing around that, than trying to force it the other way, for exactly this reason.Put another way: using a commercial supply, then adding a PoL (point of load) converter for example, can be well worthwhile, even though it's technically more complex. Kind of the electronic equivalent of software abstraction layers; it could be technically simpler, but each layer handles a certain amount of complexity that then doesn't need to be considered by the layer below it, simplifying use.As for learning -- for learning's sake -- please do! If you're going into this career, there still may not be many times you need to design a whole offline supply, but it's a steep learning curve to make one, and coming prepared makes all the difference. And even if you never need to design an offline supply, you can still apply the knowledge in anything from PoL regulators to motor controls and other power electronics.Like, for my part, I've made a few just to prove I can -- here's an LED light I made almost a decade ago:Very standard flyback design, has all the usual filtering, oh uh there's a fuse in there, naughty leaving that off the schematic; secondary side regulation, and a timed startup circuit for the fan (else it would brown out the controller's supply and never start up!). Feedback regulates LED current, with overtemp and overvoltage limiting.Here's a photo of the old "bench" area, showing it in use, before adding guards(!). Note the design is isolated (LV side earthed), and the offline stuff is on the inside, so the outer panels are, for the most part, safe to touch; there's just plenty of openings where errant fingers most definitely should not go...https://www.seventransistorlabs.com/Images/Bench998.jpgHere's a pic of the underside after some years in use. The LEDs have bleached the red hookup wires! Now they're only very pale pink.https://www.seventransistorlabs.com/Images/LED_Light_Later.jpgIt's even been around long enough I had to service it. Sequence of events was, I believe: the main filter cap was installed too tightly, lead stress caused it to leak (or maybe it was just that old), lead corroded off the board, and then circuit was exposed to fairly raw mains (still rectified, but fluctuating up and down wildly). This eventually led to failure of the main switch (probably overvoltage, due to lack of bypassing?), subsequently nuking the controller, and I forget what else had to be replaced.https://www.seventransistorlabs.com/Images/LED_Light_Died.jpg(Note the modular construction, a good way to prototype things. Copper clad PCB stock is used for the low inductance (ground plane everywhere!) and ease of soldering. Pads are either cut out of the top copper, or stacked on top using more bits of copper clad.)One of the downsides to SMPS is, failures cascade like this. Commercial ones almost certainly are a total loss, there's just so many things you need to replace to get it operating again.Simplified solutions like TOPSwitch regulators help in a respect, as there's almost everything in the one chip and if it blows up, it blows, replace it and try again.More recently (some years ago), I had to replace the original LEDs, cheap Chinese stuff; the phosphor had faded so badly, they were much dimmer for one, and rather purplish tinted. I used brand name high efficiency white LEDs this time. Pricey, but consider this: despite being a fraction of the size (3.6mm?), they handle more power, and run cooler. Lighting is remarkable these days; it always used to be, you got a minuscule fraction of light output and the rest was heat, you'd just design around dissipating all the power you put in. Nowadays, LEDs dissipatea sizable fraction of their electrical input as emitted light, significantly reducing the remainder (thermal loss). Awesome!And that's probably my most practical SMPS project; indeed, I use it every day. But probably the project that I'm most proud of in relation to its simplicity, is this flashlight:https://www.seventransistorlabs.com/Images/FlashlightTrio.jpgProto at bottom, PCB builds mid and top.https://www.seventransistorlabs.com/Images/Flashlight2Sch.pnghttps://www.seventransistorlabs.com/Images/Flashlight2_Schematic.pngIt's an average current mode boost converter, built entirely discrete ("gate level" if you will, so, op-amps, comparators, gates, etc. are fair game, but nothing specifically SMPS-oriented). The control implements output current regulation, LED overvoltage (open circuit protection), overtemp and input undervoltage. On a fresh cell it can deliver 10W, though the cells I have here tend to run flat enough that they saturate (UV limits throttle) at a few watts. Also originally built with those round Chinese LEDs, but I've since changed the original (proto) over to 3636 chip LEDs.What's great about this design is, the base board can be adapted to most anything, given a gate driver, and suitable feedback sensing. Here's a Ćuk converter I made for a drill:https://www.seventransistorlabs.com/Images/CukHack5.jpghttps://www.seventransistorlabs.com/Images/CukHack6.jpg12V input, 18V output, >200W capacity. Some fly wires and cut traces are all that's needed to mod the flashlight board into this application; the power section was sawed off to fit it into the project box. Gate drive on the flying board, going to the inverter in the bottom. Note the multiple electrolytics; they're mandatory to handle the high ripple current this thing makes in operation. The earlier version, I tried too hard to pack it into an undersized enclosure, and could only find space for one capacitor each (input and output). Turns out, the one capacitor didn't like that:https://www.seventransistorlabs.com/Images/CukHack4.jpgThe capacitor would've been running hot enough as it was, but it turns out its wire lead was actually the first to go -- it fused open!Oh, and this is also temperature protected (the blue wire pair here, can't tell which in the others, they're all black and white). Not a bad idea with the powdered iron inductor in there -- core loss is rather high. I only ever used this intermittently, so that was fine. I don't think any part can really heat up fast enough to cause damage before the thermistor notices it, though I didn't actually do a continuous load test to be sure.As a learning exercise -- this circuit is quite excellent, as it's the easiest most reliable version of a controller [current mode control], and it's built out so you can probe everything going on internally without having to reason out what's going on in the block diagram of something like UC3842, let alone anything more advanced.TL494 is quite simple as well, but beware it's never shown in a current-mode configuration -- it can be used that way, with the addition of an error amplifier to do the output regulation.Tim

author: strawberry
author_rank: Super Contributor
timestamp: April 14, 2022, 09:15:05 pm
content: first SMPS didnt worked, kept blowing transistorsin theory it should work but in practice any fix will make it worse(fun electronics)properly designed SMPS will last for minimum ~20 yearsmost likely doing electronics '' in the end you will most likely just create/copy an existing design. ''

author: sahko123
author_rank: Frequent Contributor
timestamp: April 14, 2022, 10:40:12 pm
content: Reading this has given me a bit more confidence. I think the combo I have going should work™.Do you reckon in your design you would be able to get the feedback from the auxiliary instead of the output side? Of course sacrificing output regulation but in my use case the actual voltage regulation isn't important since its just used as a high power source and it would be stepped down to 5v from 12v for some logic through an ldo anyway.I'll probably follow up with an initial circuit using the controller and transformer and maybe even a preliminary pcb design to more show off what I want (excluding pfc for now).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 14, 2022, 11:44:42 pm
content: Yes, and that is done from time to time. Regulation is worse, because the loads don't track: aux has little load in general, while the secondary is, well, whatever. Thus the leakage inductance between sec/aux have different voltage drops, and thus regulation depends critically on this parameter. Minimize leakage (more specifically: maximize pri-aux leakage while minimizing sec-aux leakage*) to get a more representative measure secondary voltage.It can also be sampled midway along the waveform, which isn't the easiest thing to do with analog circuitry, but some chips do this internally, like some TOPSwitches, or whichever ones they are (Power Integrations has many lines of these little regulators, I forget which exactly) that do opto-less regulation with pretty good performance. The smaller ones don't even need an aux winding (being directly line-powered -- at fair expense to efficiency, but when you just need one wattat all, efficiency isn't such a big deal).And yeah, regulation might not matter if you have a secondary regulator(s). Mind that you need a minimum load on the secondary, so that leading-edge spikes don't overcharge it.*About leakage: in general, there is a symmetrical matrix for leakage between any given pair of windings. There is also the property that the leakage between any triples, quads, etc. of windings cannot be more than their pairwise totals, because obviously they can't be any less coupled than the couplings between them. So, for three windings, pri-aux <= pri-sec + sec-aux, right.Put another way: consider two completely separate transformers, wired back-to-back. You have leakage P-S for the first, and leakage P-S for the second. The total leakage adds, and isn't any less than that. If the transformers were coupled together, the P1-S2 leakage could be lower than this sum.The usual way you would arrange this, is by winding the primary first, then secondary, then aux, all in single layers (more or less, as is feasible, anyway). The secondary acts to shield some of the primary leakage flux, or simply put, the aux is closer to sec than pri.Tim

author: jonpaul
author_rank: Super Contributor
timestamp: April 15, 2022, 01:26:47 am
content: Bonjour cher MonsieurBeen designing and manufacturing SMPS, electronic ballast and HV magnetics and circuits since 1970s.Bravo for,the efforts and initiativesSuggest that you first study a good text on SMPS and magnetic design before proceeding further.Off the shelf magnetics are available from Coilcraft and Pulse Engineering in USA but very limited range.At 100 w just a flyback is fine.Bridge or double Foward needed at 500 w and up.Special test equipment and probes, and mains isolation transformers are essential to.debug and,ESPECIALLY FOR SAFETY.A 360 VDC bus is LETHALbon courageJon

author: sahko123
author_rank: Frequent Contributor
timestamp: April 15, 2022, 02:10:15 pm
content: mmmmmmmm......Depending on how wide the Max and Min loads can be apart from each other it might make designing/using an smps be a waste of time since the variation would probably be anywhere between 5W to 120W peak power usage. I think this basically forces me into using a mains transformer and a secondary side power regulation......Would that wide a power range be too dangerous/impractical to operate the smps at?

author: bdunham7
author_rank: Super Contributor
timestamp: April 15, 2022, 03:11:04 pm
content: Quote from: sahko123 on April 15, 2022, 02:10:15 pm5 to 120W shouldn't be a problem for any garden-variety SMPS, 5W minimum load should be plenty for any general-purpose design. It's done all the time and one of the features of the controller you've picked is low no-load power consumption. Not using opto-isolator sensing might be the one thing that would make regulation with wide power ranges more difficult--why do you want to eliminate the opto? Even cheap-ish, crap-ish commodity SMPS designs use them.QuoteI'd have even more confidence if you'd picked a controller from the list in the transformer datasheet!But if you just use one of the schematics in the datasheet, mutatis mutandis, perhaps it will fire up. If you do, I'd be very curious to see what frequencies it ends up operating at under various load conditions--I'm not sure that transformer will work well at 500kHz just based on its size.

author: sahko123
author_rank: Frequent Contributor
timestamp: April 15, 2022, 04:20:55 pm
content: The driver the transformer recommends for 140W operation is basically not available anywhere but ebay and comes in a massive pentawatt package. Seems like this is more effort than its actually worth. I dont really want to buy an off the shelf smps cause then i'll have to pay for that myself otherwise work will pay for components.

author: TimNJ
author_rank: Super Contributor
timestamp: April 15, 2022, 05:09:37 pm
content: Are you admitting to embezzling work funds on a public forum? Anyway, I think there is a lot of useful advise already given in this thread - suggest you really read through it again. 140W power supply can be as little as $50USD for a decent one.https://www.digikey.com/en/products/detail/mean-well-usa-inc/RPS-200-24/7706036I'm not sure what size controller/MOSFET you are expecting. 140W flyback is going to require a heatsinked power MOSFET so a "Pentawatt" (TO-220) sounds about right.

author: bdunham7
author_rank: Super Contributor
timestamp: April 15, 2022, 06:10:46 pm
content: Quote from: sahko123 on April 15, 2022, 04:20:55 pmhttps://www.newark.com/power-integrations/top247yn/ac-dc-conv-125w-40-to-150deg-c/dp/93K0787?gclid=Cj0KCQjwr-SSBhC9ARIsANhzu17ks2rNJSTx89mvWmTcd-Ki7aE53cgXuFd2HUTJT0OaKNEvAjZbUfUaAqtUEALw_wcB&mckv=s_dc|pcrid|486536532942|plid||kword|top247yn|match|p|slid||product||pgrid|113542825414|ptaid|kwd-10769551587|&CMP=KNC-GUSA-GEN-SKU-Semiconductors-Semiconductors-ICs&cmp=KNC-GUSA-GEN-SKU-Semiconductors-Semiconductors-ICshttps://www.farnell.com/datasheets/1498742.pdfI don't think you're going to find a solution that is easier or cheaper to implement than that for a MyFirstSMPSTM. Just throw it together and it might work. And a 140W flyback is going to need to dissipate 40W+ power unless you are very successful in your first try and somehow achieve some remarkable efficiency. I'm sure there's a large heatsink and likely a fan involved no matter what you do.

author: sahko123
author_rank: Frequent Contributor
timestamp: April 16, 2022, 05:38:36 pm
content: Yeah going through the datasheet this TOP2XX series of switchers has got basically an entire design procedure and more than just the to-220 (penta-watt) package. Its literally the perfect controller/driver cause you can get it for power ratings from like 10W to 250W with active cooling don't know why I struggled to find a decent datasheet.

author: sahko123
author_rank: Frequent Contributor
timestamp: April 17, 2022, 01:14:27 am
content: Also what limits the power rating of a transformer? Is it a matter of how its driven or is there a characteristic inherent to the transformer that decides it's theoretical maximum limit for power or does it involve both?I understand there is a saturation current but that wouldn't mean that if, for example a 4A saturation current with a primary side DCV of 340Vdc wouldn't give you a potential of 1360W wouldn't it?So essentially to what extent is the topology a limiting factor and to what extent is the transformer the limiting factor?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 17, 2022, 02:34:45 am
content: As mentioned, maximum power depends on loss. You can crank more voltage by raising frequency (up to the peak power point*), but this raises core loss (significantly). You can crank more current but the wire gets hotter, at least for transformers. Inductors, you can't get much beyond saturation, as the nonlinear inductance is messier to work with and likely the core loss limit isn't much beyond.*Depending on transformer design, like, winding strays. At a high enough frequency, capacitance or transmission line effects dominate and gain and power handling will drop. Also current flows will be very nonuniform over the windings, making heating even worse.Normally, a transformer is designed for nominal ratings, so, some tolerable heating or efficiency spec, at operating frequency, current, voltage and so on. It can be used at other values, but gets proportionally worse in the process. Flyback being the least critical, so the voltages there are kind of a suggestion, but you really want a proper part if you're using it more than say 2:1 off the suggested rating. Or for forward, obviously if you need more voltage, you just can't get more than full duty cycle would give, but less is fine.Tim

author: sahko123
author_rank: Frequent Contributor
timestamp: April 18, 2022, 08:13:41 pm
content: So now I guess the last thing there to do is make the circuit with the transformer I found and the TOP271 controller and just see how much current I can pull out of it before it either pops or begins to drop voltage at an uncomfortable rate.

author: strawberry
author_rank: Super Contributor
timestamp: April 19, 2022, 12:18:48 am
content: no voltage drop should happen (only due to wires) . overcurrent protection will shut off SMPS .too big device TOP271 will have too high minimum current limit setting . core will go into saturation and MOSFET will POP instantly .no chance pushing limits out of flyback without proper math .

author: David Hess
author_rank: Super Contributor
timestamp: April 19, 2022, 02:34:08 am
content: Quote from: sahko123 on April 13, 2022, 02:40:30 pmThe saturation current has nothing to do with power capability.The maximum power depends on core losses which depend on frequency and peak flux. There should be a series of curves from the manufacturer in the specifications. Power is proportional to frequency, but because core losses are also proportional to frequency, peak flux must be lowered which lowers the power.Quote from: sahko123 on April 13, 2022, 08:09:17 pmConsider prototyping a design at a lower input voltage using a standard 60 Hz power transformer for isolation. I also recommend wearing a face shield during testing if you use plastic power packages.

author: sahko123
author_rank: Frequent Contributor
timestamp: April 19, 2022, 08:52:56 am
content: The datasheets are very lackluster. I've found two different variations both of which a max peak current of 4A so I assume that the saturation current of the transformer. And going on the manufacturers website it states the transformer is 90W and not 120W/140W like other retailers say. So it probably isn't even worth laying money down for at this pointhttps://www.tme.eu/Document/078417cb0a3500f1b3b48fc4dd20480a/74060-Datasheet.pdfhttps://www.farnell.com/datasheets/484382.pdfI don't understand why this has to be so difficult.

author: strawberry
author_rank: Super Contributor
timestamp: April 19, 2022, 03:41:44 pm
content: 90W@66kHz , 140W@132kHzinductance seems too high for universal line voltage at 132kHzETD39 DIY transformer would cost half that of MYRRA

author: TimNJ
author_rank: Super Contributor
timestamp: April 19, 2022, 04:21:22 pm
content: Try simulating first. A lot of your questions and confusion comes from not really understanding what you are trying to do.https://www.analog.com/en/products/lt8316.html#product-toolsOpen the file:LT8316 Demo Circuit - µPower No-Opto Isolated Flyback Converter (100-600V to 12V @ 1.5A)You can visualize some of the standard flyback waveforms, adjust parameters and see what happens.

author: jonpaul
author_rank: Super Contributor
timestamp: April 22, 2022, 07:00:36 am
content: Rebonjour à tousJust seeing thisOur experience since 1970s, at high power SMPS transformers.....Saturation is not approached, even at max primary volt seconds.Power handling is set by worst case hotspot, and insulation class, (classe 105, 130, 150) and regulatory complianceThe old rule of thumb was design worst case load, etc, for equal copper loss and core loss.Nowadays that is not an optimal ratio, but a good starting point.Of course in a high frequency SMPS transformers or inductor Pcu must include IsqR, skin and proximité effect, and consider the substantial temp coefficient of the copper.Thus a transformer's design power rating is not quite as simple as mentioned.Most ferrite core and materials specs include curves of,losses vs excitation and temperature, to,find,an optimal hotspot temperature as well as flux densité in typical application.Check spec of core matériel and core shape from manufacturer, like TDK, NiCera, Philips, SiemensOld catalogues should have that informationFinally the only Simulator and CAD,we have used was,Intusoft, Magnetic Designer, available gratuit.Bon courageJon

author: sahko123
author_rank: Frequent Contributor
timestamp: April 25, 2022, 12:05:52 am
content: Update:I have fallen into the rabbit hole. I bought the Wurth Elektronik: Trilogy of Magnetics and oh boy.....So for the initial project (A JBC T245 soldering iron base station) I ended up buying a power supply that is a good fit both physically and electrically. But I shall carry on falling into the rabbit hole by designing and winding a transformer based on my reading of the Trilogy of Magnetics (Amazing treasure trove on both power supply design and transformer winding). Probably at first I'll try get it to work at 48V input or something lower and work my way up designing for offline supplies and the likes.I'm basically going to keep digging down until I reach the center of the earth.