Virtual 240Vac Bipolar Active Zener to Extend the SMPS High Voltage Limit - Page 1
Forum section: electronics / projects

author: KerimF
author_rank: Frequent Contributor
timestamp: October 17, 2023, 09:38:57 am
content: Hi,The presented circuit (attached as PDF) will be connected in series to the protected SMPS (AC to DC Switch-Mode Power Supply). It is surprising that it will act as if it is a bipolar hi-voltage zener connected in parallel to it. It works from about 100 to 400 Vac. Below 240Vac (the adjusted hi-limit, as Vpeak=340V), the circuit (in series) looks as a short- circuit between mains supply and the SMPS.I am afraid that unless it is possible to model the AC input of an SMPS properly, a simulator (as LTspice) won’t give the real trace of the voltage on the SMPS input (50Hz sinewave clipped at the adjusted limit voltage in each half cycle). The real trace (when mains voltage is above the voltage limit) can be seen on an oscilloscope.I shared this topology here with the hope that someone may know a simpler way to achieve this function.Thank you.KerimEdited:A simple overvoltage protection is presented on post #11

author: coromonadalix
author_rank: Super Contributor
timestamp: October 17, 2023, 04:24:16 pm
content: you want to limit the input voltage of the smps outside the main ac voltagepersonally i don't understand where your going, you can use scr controlled rectifiers or even triac controlled rectifier bridgesin no way your irfp460 circuit is bipolar, since you have a protection diode in the mosfet ??or you want to limit the inrush current ??https://www.radiolocman.com/shem/schematics.html?di=183767

author: KerimF
author_rank: Frequent Contributor
timestamp: October 17, 2023, 05:06:46 pm
content: Quote from: coromonadalix on October 17, 2023, 04:24:16 pmSorry for not being clearer.Let us suppose a conventional (Chinese) SMPS may be supplied, by mistake or due to an electric fault, by a relatively high voltage (say >240V up to 400V). This circuit, if connected in series, clips the AC voltage at its input (say at +/- 340V, the peak of 240Vrms). This is equivalent to a virtual bipolar hi-voltage zener connected in parallel at its input.The added 4-diode bridge lets the MOSFET acts as a bipolar device.A triac cannot clip the top of an AC supply voltage when it exceeds a certain limit (as the peak of 240Vrms). it can vary its RMS value only, not its peak (unless the phase delay of the trigger pulse is made greater than 90 degrees).This circuit is not about protecting from inrush current but from overvoltage.

author: Kim Christensen
author_rank: Super Contributor
timestamp: October 17, 2023, 05:31:40 pm
content: Sounds like you need fuse in series and a MOV across the AC input of the SMPS.

author: DavidAlfa
author_rank: Super Contributor
timestamp: October 17, 2023, 05:39:56 pm
content: Search "ac crowbar protection circuit".

author: KerimF
author_rank: Frequent Contributor
timestamp: October 17, 2023, 05:40:12 pm
content: Quote from: Kim Christensen on October 17, 2023, 05:31:40 pmGood solution, but the purpose of this circuit is to keep the SMPS running (its DC supply not interrupted) even if the mains voltage becomes relatively very high (up to 400Vrms).

author: coromonadalix
author_rank: Super Contributor
timestamp: October 17, 2023, 05:40:56 pm
content: some smps can handle some spikes at 400v if you have some crap not sure lollsome will work from 85-100 vac up to 265 vacyou have power bars or line filters who will kill some of theses spikessound like you want some line conditioner to avoid those surges, an active solution you could saysome solutionhttps://www.littelfuse.com/~/media/electronics/application_notes/littelfuse_high_power_semiconductor_crowbar_protector_for_ac_power_line_application_note.pdf.pdf

author: KerimF
author_rank: Frequent Contributor
timestamp: October 17, 2023, 05:50:03 pm
content: Quote from: DavidAlfa on October 17, 2023, 05:39:56 pmThank you for the hint.But I wonder if such a circuit will keep the SMPS running and supplying its DC voltage to a controller board while the mains voltage is high (say 380Vac).Please note that the circuit, presented earlier, is not just a protecting one but regulating as well.

author: DavidAlfa
author_rank: Super Contributor
timestamp: October 17, 2023, 06:01:03 pm
content: No, it's just a protection, blowing the fuse instead burning everything.Neither does your original circuit, trying to clamp mains can only end in fire, the power from mains is virtually unlimited, so if it supplied 400V and you tried to clamp it down to 200V, it would need hundreds of amps.If you need it to keep operating under overvoltage condition, then properly design it so it can work at 400V.

author: KerimF
author_rank: Frequent Contributor
timestamp: October 17, 2023, 06:05:49 pm
content: Quote from: coromonadalix on October 17, 2023, 05:40:56 pmI needed to design the OP circuit because I produce mains stabilizers for houses and offices whose input could be 290V down to 110V (50Hz). Their controllers are supplied by conventional (economical) AC-DC SMPS. And I liked that the 3+3-digit LED display of their controller shows the input voltage even if it becomes as high as 400V (extreme possible limit!). I did it by regulating the peak of the AC voltage supplying the SMPS.

author: KerimF
author_rank: Frequent Contributor
timestamp: October 17, 2023, 06:24:15 pm
content: I corrected the title of the topic.Based on what I heard so far, I realized that the word 'protect' in the original title was misleading. Sorry for any inconvenience.

author: KerimF
author_rank: Frequent Contributor
timestamp: October 18, 2023, 07:17:29 am
content: By the way, in my low-cost mains stabilizers, I simply protect the SMPS by a simple circuit (attached as PDF). It just cuts the mains supply when the mains voltage reaches a high voltage (as 250Vac, for example). It is much like a mechanical breaker but for overvoltage.If its 24Vdc relay is somehow sensitive (it turns on at a DC voltage around 15V or below), a 1/2W resistor (not shown on the schematic) is added in parallel to 470uF (CP1). Its value (usually between 3K3 and 10K) needs to be found empirically so that the 5K trimmer (RV1) covers the range around the desired AC voltage limit. For instance, the DC voltage on the relay coil will be around 24V @380Vrms (50Hz).

author: KerimF
author_rank: Frequent Contributor
timestamp: October 18, 2023, 08:13:04 am
content: Quote from: DavidAlfa on October 17, 2023, 06:01:03 pmYou are totally right in case a circuit is connected in parallel. But my original circuit is connected in series.After all, it seems that what I did is somehow a novel topology (based on the well-known saying: Necessity is the mother of...). I wonder if someone else needed to also design such an active regulator (made for small conventional SMPS, not heavy loads).So, if someone will have time (and the necessity) to build and test it, he will be surprised (as it happened to me while watching its regulation on the oscilloscope screen for the first time) how a series circuit could act as a virtual zener connected in parallel which also clamps the top of the high voltage sinewave.

author: soldar
author_rank: Super Contributor
timestamp: October 18, 2023, 08:25:32 am
content: Quote from: KerimF on October 18, 2023, 08:13:04 amThen it is not acting as a zener. You are using that word very loosely and confusingly.

author: KerimF
author_rank: Frequent Contributor
timestamp: October 18, 2023, 08:47:20 am
content: Quote from: soldar on October 18, 2023, 08:25:32 amI understand your confusion.I usually add LTspice files to simulate the circuit I present.Unfortunately, here there is no good model to emulate the input of a conventional SMPS. Do you think it could be done?So, for the time being in the least, the only way to see how this real circuit (in series) acts if it were a bipolar zener connected in parallel is by building it then testing it (with an SMPS as a load in series) by using a scope to see the positive and negative flat tops of the regulated AC voltage when the high limit is exceeded. Otherwise, it is very hard for someone to get how it works.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 18, 2023, 09:29:11 am
content: I don't quite understand "220V" being wired to a CD4093 logic gate.Better names I guess would be "220V" --> "HOT", "NTR" --> "NEUTRAL", "SMPS" --> "LOAD"; "220V" net bridged to a "VDD" or something like that, and "GND" can be a high side VEE, or floating GND or something like that, maybe it's fine to leave as "GND" as such but just as long as it's clear. A connected drawing would be easier to make sense of than net labels, making it clear that the logic side is "hanging below" one AC line, and there is a series bridge element connecting the load.So I guess the point is a dropper to limit load voltage? But this is exactly inverse to a zener shunt, not equivalent to it!What current range? What fault current capacity? Not much I guess given the 1N4007s, and the poor IRFP460 will expire rather quickly under any kind of startup conditions, but maybe it'll last long enough to start a small (10s of W?) SMPS, I don't know.The problem with putting absolutely any kind of semiconductor directly on the mains, is transients. You need at least a 1.2kV rating, with generous MOVs provided; at 400V, you're probably asking closer to 2.5kV. Even with SiC MOSFETs and a generous budget, this is a huge ask, just in switching capacity, let alone in linear operation. SiC do at least switch quickly, which suggests a more promising route: make an AC buck converter with current and voltage limiting behavior; the dropped power still must be dissipated, but it can be clamped by diodes and dumped into a generously sized resistor if nothing else.Such a gross error (literallywired to the wrong power source) is best solved by a similarly gross corrective method: relay switching, or fusing. Perhaps this device is promising in certain settings, but without those circumstances set out, without any motivation, without any specification -- it just sounds like a poor attempt to deal with something that should never, ever be a "nuisance" anywhere on the planet.Tim

author: soldar
author_rank: Super Contributor
timestamp: October 18, 2023, 10:19:31 am
content: Quote from: KerimF on October 18, 2023, 08:47:20 amAgain, if you are trying to do what I think you are trying to do, you are expressing it in a very confusing way which I would interpret as you not being entirely clear and being beyond your limits.You say you want like a zener in parallel except it would not be in parallel and not be a zener. That makes no sense.It seems to me you just want to limit the voltage. The fact that it goes to a small wall wart SMPS is not really that important. It is probably just a load with a rectifier bridge and capacitor. You are probably focusing on unimportant points.One way to stabilize voltage is with ferroresonant transformerhttps://www.sunpower-uk.com/glossary/what-is-a-ferroresonant-power-supply/https://voltage-disturbance.com/power-engineering/ferroresonant-transformer/https: // www. youtube. com/watch?v=T5Je6l-OaoQ

author: KerimF
author_rank: Frequent Contributor
timestamp: October 18, 2023, 11:29:01 am
content: Quote from: T3sl4co1l on October 18, 2023, 09:29:11 amTo let the SMPS be connected to neutral (not floating), I decided to let my circuit be the floating one. So, its ground is connected to the hot line.You are right. The word '220V' is misleading here. But my assistants whose English is rather very weak are used to hear it (220V) as being 'the hot line'.Quote from: T3sl4co1l on October 18, 2023, 09:29:11 amAll you said makes sense. But when I drew it, after many other design failures and for in-house use only (that is just for me), I didn't notice that its schematic became clear to me onlyPlease note that the regulating circuit is done for SMPS specifically (not any load). Therefore, no one here will likely be interested in keeping a conventional 220V SMPS running normally at high voltages. Usuallly, a simple passive protecting circuit (as the one at post #11, for example) could be enough in most applications.Quote from: T3sl4co1l on October 18, 2023, 09:29:11 amYes, it is a voltage dropper in series but, as I explained many times earlier, its end effect is of a bipolar zener (the positive and negative tops of the voltage sinewave are clamped, so two flat tops could be seen, exactly what a bipolar zener is supposed to do).Yes, it is not a zener. It just regulates the AC high voltage as if it were a bipolar zener. This is why I added the word 'Virtual' in the OP title.Quote from: T3sl4co1l on October 18, 2023, 09:29:11 amIt is not a general-purpose regulator. It was done for small SMPS supplies only.Quote from: T3sl4co1l on October 18, 2023, 09:29:11 amYour remarks are interesting. If I was born and live elsewhere, I would likely need to observe them. So far, the circuit, as it is, seems working fine in my surrounding (local consumers).Quote from: T3sl4co1l on October 18, 2023, 09:29:11 amI agree with you. It was not done/designed for a NASA programAbout nuisance, I am afraid that, if we are realistic, there are always new devices which are created and made, almost daily, just for it

author: coromonadalix
author_rank: Super Contributor
timestamp: October 18, 2023, 11:47:55 am
content: well instead of creating it, just buy such device ... you have active line stabilizers / protectors etc ... they are certified and tested ....You don't provide enough knowledge, nor protections, nor insurances this project will work as intended,For myself i would not use such a DIY design if you will use it say for professional use or protect some smps used somewhere etc ...the implications ... the safety etc ...too much misleading information, bad wording, sentences corrections, etc .... this thread should not be pursued ...no one will take the risk helping you like this, and in case of something happens ....my 2 cents, sorry

author: KerimF
author_rank: Frequent Contributor
timestamp: October 18, 2023, 12:16:49 pm
content: Quote from: soldar on October 18, 2023, 10:19:31 amSorry, I don't try doing anything. It happened that after the circuit was designed and done, it works on the regulated sinewave voltageas ifit were a parallel bipolar zener while it is actually connected in series. Isn't this weird. Yes, it is. I personally didn't expect this result. But a fact is a fact. I wouldn't believe it if I didn't test it and saw how the regulated top was clamped as a virtual bipolar zener in parallel is supposed to do.Quote from: soldar on October 18, 2023, 10:19:31 amAn SMPS supply (24V/2A for example), working from 100Vac up to about 240Vac, may not be important to most engineers. On my side, I use it to supply most of the controller boards in my products.Quote from: soldar on October 18, 2023, 10:19:31 amThank you for your suggested good solutions. In these days (since after year 2011), it becomes hard to me, where I live, to get ferro transformers. So, I used to avoid using them in my new designs. I just use the components that could be available locally, in every period of time (for this, I had to also update my designs. one a while).

author: KerimF
author_rank: Frequent Contributor
timestamp: October 18, 2023, 12:35:41 pm
content: Quote from: coromonadalix on October 18, 2023, 11:47:55 amAll you said makes sense.It just happens that we have no choice but to live in two very different worlds while we are on the same planet.In brief, what seems good or bad to you, or what could be available to you or not... may not be so to me. Why? I am afraid it is a big topic and could be discussed rationally among 2 or 3 persons at most... surely not in a forum.Anyway, thank you for your sincerity.

author: soldar
author_rank: Super Contributor
timestamp: October 18, 2023, 12:39:17 pm
content: Quote from: KerimF on October 18, 2023, 12:16:49 pmI mean it is not really relevant to the issue of limiting maximum voltage.If you are trying to supply power to a device that will take between 100 and 240 V and you want to prevent the mains 230V going over voltage then you can put a transformer (or autotransformer) that will reduce the voltage from 230V nominal to, say, 160V. That way you are sure to never go over voltage.

author: temperance
author_rank: Super Contributor
timestamp: October 18, 2023, 12:58:35 pm
content: Is there a valid reason for you to not just develop your own SMPS capable of doing exactly what you need? Switcher with integrated 700V rated MOSFET's are available for peanuts.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 18, 2023, 01:52:42 pm
content: Quote from: temperance on October 18, 2023, 12:58:35 pmI suspect the answer is again availability. OP doesn't give background (and, perhaps, has many reasons not to), but if we were to read into their country flag a little, we might guess they aren't in a very familiar (to western minds), or orderly, or even peaceful, environment.Reading into that flag a bit further still, we might also expect reasons why OP is reluctant to give more details -- whether because middle-east anything is a "hot button" political topic (which, to be fair, a pretty sizable number of people here are capable of having a peaceful and nuanced conversation over; but due to the few whocannot, we generally shy away from such topics entirely), or even for reasons of personal security (whether giving more detail would create personal risk, e.g. deanonymizing, or indeed be seen as criticizing the local powers-that-be and thus a direct threat).And, for the record, and by all means, do read this as a benefit of a doubt -- you have all my sympathy, being in such a contested region; my above reply is simply what it is, a response to the information as given, without trying to make much assumption about it.Tim

author: soldar
author_rank: Super Contributor
timestamp: October 18, 2023, 02:15:32 pm
content: Quote from: temperance on October 18, 2023, 12:58:35 pmBesides the point of limited availability I would recommend adapting the input voltage to the device rather than trying to design and build a new device. It is much simpler to lower the voltage than it is to design and build a SMPS. Pretty much anyone can use a transformer to lower voltage but it takes a very specialized and experienced engineer to design a good SMPS. Not to mention the availability of special ferrite transformers, etc.

author: KerimF
author_rank: Frequent Contributor
timestamp: October 18, 2023, 02:16:45 pm
content: Quote from: soldar on October 18, 2023, 12:39:17 pmIn this case, let us calculate the acceptable minimum mains voltage:Vmin = 100V [minimum for SMPS] * 230 / 160 = 143.75 VAnd let us calculate the acceptable maximum mains voltage:Vmax = 250 [typical maximum for SMPS] * 230 / 160 =359.375VIn general, these two limits look reasonable.The problem is that local consumers used to buy mains stabilizers working from 110V up to 290V (16-step model by using 4 relays). And above 290V, the saturation high current of their transformer opens their main breaker. These stabilizers don't use an external DC supply. Their controller is supplied by a low AC voltage taken from their main power transformer. Therefore, their protecting power relay has to be at the output, not input (hot line).To compete in the local market, I let my controllers and their display work normally from 100V to 400V. The input of the stabilizer, excluding its SMPS, is isolated completely from mains by a protecting power relay if the Vac > 290V or below 110V). Things will return back to normal when the mains voltage returns back within limits (no need to switch/close an open mechanical breaker after a mains overvoltage).For instance, ordering or making a special small transformer is not economical on my side.

author: KerimF
author_rank: Frequent Contributor
timestamp: October 18, 2023, 02:37:44 pm
content: Quote from: temperance on October 18, 2023, 12:58:35 pmOf course, there is a valid reason on my sideA practical SMPS needs a ferrite transformer. In these days, I have no more the privilege to order such components from abroad (this was possible before year 2011). Now, the local retailers provide them with unknown characteristics and in small quantities for each type.

author: soldar
author_rank: Super Contributor
timestamp: October 18, 2023, 02:42:51 pm
content: Quote from: KerimF on October 18, 2023, 02:16:45 pmI realize there is a bit of a language problem but I think I am only now beginning to understand what you want to do. You are not explaining it very clearly.You want a device that is connected to the mains and disconnects the load when voltage is under a voltage V1 or over another voltage V2 and connects the load when the voltage is between these values.Is this what you want to do?I cannot imagine living somewhere where the mains voltage is so unstable. That has to damage all sorts of appliances and electronics.

author: coromonadalix
author_rank: Super Contributor
timestamp: October 18, 2023, 04:33:19 pm
content: exactly my toughts i what i wrote earlier is not country specific, its just a matter of doing things properly with official and reliable tools, they exists and doesn't cost a fortuneyou did receive very good answers, and telling you are in say dire position monetary / political / other ... and not telling the full story is not helping you ... i can understand youbut here right now, you ask for advise / help and you are still mysterious or vague in some instance(s)you play with voltages and or currents, this is or may be a safety concernto have huge voltages swings in ac network / main voltages is not good BUT you need voltage conditioning / limitters, once again you did receive some answers and it seems you don't want to acknowledge themhttps://www.amazon.ca/Automatic-Protector-Reconnect-Reliable-Adjustable/dp/B08RJ6JSZDhttps://www.amazon.com/Protection-Adjustable-Automatic-Reconnect-Protector/dp/B07TQH19KQ?th=1https://www.walmart.ca/en/ip/adjustable-delay-protector-automatic-relay-protector-automatic-reconnect-for-voltage-protector-home/PRD15VKYMJO27WZhttps://www.walmart.ca/en/ip/Protection-Relay-Automatic-Protector-Over-Under-Voltage-Recovery-2P-40A/PRD4CHY6XXFF2Z6and this onehttps://www.automationdirect.com/adc/overview/catalog/relays_-z-_timers/voltage_monitoring_relaysVoltage monitoring relays sense and evaluate AC single-phase (50 to 60 Hz) or DC voltages to protect equipment from fault conditions.Over/under voltage relays with fixed or adjustable time-delay drop-out will protect equipment from over- or under-voltage conditions.Voltage band relays protect equipment that is required to operate within an upper and lower voltage limit. The relay is energized and will remain that way as long as the monitored voltage remains within the adjustable range.FeaturesMonitors AC single-phase (from 90 to 600 VAC) and DC voltages (from 9 to 138 VDC)True RMS voltage measurement supports non-sinusoidal waveforms and ensures more accurate sensingAll relays offer 10A contact ratingWide range of user adjustable pick-up voltages8-pin socket mount (sold separately)LED indicates output relay statusSelect models support an adjustable drop-out delay (0.1 to 10 seconds)(VMR-2C-F-120A)anotherhttps://www.littelfuse.com/products/protection-relays-and-controls/protection-relays/voltage-monitoring-relays.aspxyou have single phase and 3 phases modelsNo offenseWith all the time and money you may lost trying to build something similar, try some already made solutions, to buy one, or try to get them shipped to you unless your country is totally isolated from the planet

author: KerimF
author_rank: Frequent Contributor
timestamp: October 18, 2023, 04:54:15 pm
content: Quote from: soldar on October 18, 2023, 02:42:51 pmNoWhat you understood from my previous post is related to the stabilizer and its load (the electrical network of a house or office).The circuit, I presented, has to keep the SMPS that supplies 24Vdc voltage to the stabilizer's controller active from 100Vac (the SMPS typical minimum) up to 400Vac (the excess power is dissipated by the power hi-voltage MOSFET). It is the job of the controller to monitor the input and output voltages (also the mains current in some models) and activate the relays as it is programmed.Quote from: soldar on October 18, 2023, 02:42:51 pmMe too, I am surprised that many consumers in my city need to install stabilizers. My mains voltage is, typically, in the range from 190V to 235V, not bad.

author: Kim Christensen
author_rank: Super Contributor
timestamp: October 18, 2023, 05:13:27 pm
content: Could you not power the SMPS from theoutputof the stabilizer? Kind of like a reverse "bootstrap" configuration.ie: The stabilizer's default mode is passthrough and it powers both the SMPS and the load.

author: KerimF
author_rank: Frequent Contributor
timestamp: October 18, 2023, 05:45:37 pm
content: Quote from: coromonadalix on October 18, 2023, 04:33:19 pmI believe this very true on your side.Quote from: coromonadalix on October 18, 2023, 04:33:19 pmIt seems my English is really bad. I thought on my OP it was clear that I 'did' an active circuit to limit the voltage at the input of an SMPS specifically, not any other load. And it works fine. My question was:"I shared this topology here with the hope that someone may know a simpler way to achieve this function."So far, it seems there are ready-made products which do the same job, if not much better. These products are likely available to most engineers around the world, but not to me.Quote from: coromonadalix on October 18, 2023, 04:33:19 pmIt is about limiting a high voltage while the load current (of a 24V/2A SMPS) is relatively very small (at its input).Quote from: coromonadalix on October 18, 2023, 04:33:19 pmCould you imagine that, due to world's regulations, all these sites (besides many others) have no right to open their door if knocked by someone living where I am? Otherwise, they broke the rules of their authorities. So, I have no reason to blame them.Quote from: coromonadalix on October 18, 2023, 04:33:19 pmAt last, you got my real situation well as you defined it by your last sentenceFor instance, this forum is the last technical one that allowed me to join it and be its guest till now.

author: KerimF
author_rank: Frequent Contributor
timestamp: October 18, 2023, 06:06:11 pm
content: Quote from: Kim Christensen on October 18, 2023, 05:13:27 pmIn this case there will be no need to use an external SMPS. I mentioned on reply #25:"These stabilizers(not designed by me)don't use an external DC supply. Their controller is supplied by a low AC voltage taken from their main power transformer. Therefore, their protecting power relay has to be at the output, not input (hot line)."Converting AC to DC is done on their controller. So, in case of a fault on the mains line, the high voltage saturates the power transformer, and the resulting high current opens their main breaker. I simply liked to avoid this to let my stabilizer full automatic after any situation,

author: temperance
author_rank: Super Contributor
timestamp: October 18, 2023, 06:19:45 pm
content: The easiest solution to your problem is a source follower. Just a bridge rectifier, a zener, a couple resistors and a MOSFET and some inrush current limiter.I can't seem to come up with a better schematic than this one:https://electronics.stackexchange.com/questions/553703/source-follower-large-signal-analysis-as-level-shifterVin is derived from the mains supply with a zener diodes and a resistor. The voltage across Rs (your SMPS) will be at 2...5 V below the zener voltage.

author: DavidAlfa
author_rank: Super Contributor
timestamp: October 18, 2023, 07:09:44 pm
content: Still no way you're clamping the mains, forget that idea right now.What's the power of the smps?You could make some sort of high voltage linear regulator, so that the transistor acts as a series resistor.This will create a lot of heat, so meant for short durations events only (spikes, sudden changes).A proper solution? A PFC circuit that produces stable DC output over a wide range of input voltages, then feed this DC to your smps.

author: Kim Christensen
author_rank: Super Contributor
timestamp: October 18, 2023, 07:49:49 pm
content: Quote from: KerimF on October 18, 2023, 06:06:11 pmNo.. Usingyour"stabilizer" to poweryourSMPS which powersyour"stabilizer"...ie: On startup, and if input line voltage is lower than 250VAC, the SMPS is connected to the line input via a DPDT relay. The SMPS powers your stabilizer and after a delay, the DPDT relay switches over so the SMPS is now powered by the output of your stabilizer. Now, your line voltage can vary up and down while your stabilizer keeps the voltage on the load and SMPS steady.If the input voltage goes too high, your system shuts off, but the SMPS does not get reconnected to the line until the input voltage drops below 250VAC. So the input voltage has to drop below 250VAC before the system will auto restart.

author: BrokenYugo
author_rank: Super Contributor
timestamp: October 18, 2023, 08:31:51 pm
content: If I'm understanding right what OP is after is a sort of preregulator for the control circuit PSU of a whole house mains tap changer voltage stabilizer. So they can use an available supply that can't handle more than 240V. They cannot use the output of the stabilizer because they want the power supply live full time, so the tap changer can connect and disconnect from the grid as the voltage goes in and out of the limits of the tap changer's transformer, rather than put the transformer into saturation and trip the breaker feeding it as their competitor's designs do.I think the easiest solution is probably to rectify and buck down the mains to a reasonable value, then feed that DC to the SMPS, not sure that quite qualifies as PFC as DavidAlfa suggested, but it should work and the inductor is much simpler.

author: temperance
author_rank: Super Contributor
timestamp: October 19, 2023, 01:35:49 am
content: @DavidAlfaQuoteYou seem rather beta when it comes to reading because that's exactly what I suggested above what you posted

author: DavidAlfa
author_rank: Super Contributor
timestamp: October 19, 2023, 02:10:45 am
content: Well, my apologies, sometimes it's just too long, please send patent documentation to proceed with IP infringement claim

author: KerimF
author_rank: Frequent Contributor
timestamp: October 19, 2023, 06:28:20 am
content: Quote from: temperance on October 18, 2023, 06:19:45 pmThank you for your suggestion. Right now, this webpage doesn't open properly on my side. I will try it later.By the way, the proposed topology seems somehow similar to the one I attached on my first post; same components (excluding the inrush current limiter).

author: KerimF
author_rank: Frequent Contributor
timestamp: October 19, 2023, 07:06:26 am
content: Quote from: DavidAlfa on October 18, 2023, 07:09:44 pmIn my solution (attached at OP), the MOSFET acts as a dynamic series resistor. You are right, this creates heat up to 10W (@400Vac). But this is not too bad knowing that the mains voltage is below 250Vac most of the time. And a high voltage on the mains line doesn't last for long. The SMPS power is usually 50W (24V/2A DC output) or less. So, its maximum input current is below 1/4 A (mains, 220V 50Hz).Yes, using a PFC circuit is a very good solution. But it uses a ferrite transformer which I can't get easily in these days for many reasons.

author: KerimF
author_rank: Frequent Contributor
timestamp: October 19, 2023, 08:04:53 am
content: Quote from: Kim Christensen on October 18, 2023, 07:49:49 pmIt seems a good solution.So, let us go on to some details.On startup, there is a circuit that monitors the input line voltage.This startup circuit should be designed for the worst case (Vin=400Vac).Case 1:It turns on the DPDT relay if Vin > 250Vac, in order to disconnect the SMPS from mains. In this case, I am not sure if the very short delay (in ms) before disconnecting the SMPS could damage it or not (mainly if Vin is >300Vrms).Case 2: (opposite)It turns on the relay if Vin < 250Vac, in order to connect the SMPS to mains line. But the relay should be on even if Vin drops to about 100V. I think this could be done, speaking practically, since the relay DC holding current is usually much lower than its startup current.But, after a good startup (Vin < 250V), the high limit (250V) needs to be increased, otherwise the stabilizer won't reach its usable upper limit (about 290V).I will work on it. Thank you.Kerim

author: KerimF
author_rank: Frequent Contributor
timestamp: October 19, 2023, 08:22:18 am
content: Quote from: BrokenYugo on October 18, 2023, 08:31:51 pmUnfortunately, I have to avoid, in these days, using ferrite transformers in my designs. For this reason, I had to use the E-I iron cores, instead of the ferrite ones, to produce various DC to AC power inverters (500W to 2KW).

author: KerimF
author_rank: Frequent Contributor
timestamp: October 21, 2023, 12:52:27 am
content: Based on the idea of a simpler solution suggested by Kim Christensen (Reply #35), I designed a circuit that monitors the mains voltage from 100V to 400V though it supplies the SMPS from 100V to 250V only. Its main components are the two opamps of LM358, a small 24Vdc relay and two high voltage capacitors (1uF/275Vac in series, equivalent to 500nF)I drew its schematic on Kicad (attached as PDF), then on LTspice to simulate it and test if it functions as expected. I used the available model LT1006 to replace LM358.

author: KerimF
author_rank: Frequent Contributor
timestamp: May 12, 2024, 09:36:46 pm
content: Hi again,I returned to this thread because there is a new solution which lets all previous ones in it obsolete in case the SMPS unit supplies the controller of a mains stabilizer.Lately, a consumer ordered a mains voltage stabilizer (4KW, 50Hz). Its characteristics are supposed to be as the following: Its input voltage range is supposed to be 80 to 350 Vrms. Its output voltage range shouldn’t exceed 220V +/- 15V. Its controller (with 3+3 LED 7-segment digits) should work properly between 75 and 400 Vrms (consumer's mains voltage).The first  and  could be achieved by using 4 power 1P2T relays which give 16 steps (11 for up, 1 for normal and 4 for down).The challenge was to satisfy  with a simple low-cost reliable (non-mechanical) circuit to let a typical 24V/1A SMPS (rated input from 100 to 240 Vac) supply properly the stabilizer board even if the mains input voltage drops to 75V or increases up to 400V (this may happen in network faulty conditions).I ended up designing for  a circuit to be added in front of the SMPS. Its components are:16 x 1N40071 x IRFP460 (high voltage N_MOSFET)2 x 160V zener (which was available)1 x 10V zener (between the MOSFET gate and its source)In case there are some members who may be interested in such a circuit, I will draw its Kicad schematic. Then, I will upload it as PDF.Kerim

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 13, 2024, 04:39:39 am
content: What about just a solid state switch that is on when the instantaneous voltage is less than 360V or so and off when above? I have seen a similar design to make a small 120V only switching supply able to run on both 120V and 240V. Very little dissipation and almost zero switching losses.

author: KerimF
author_rank: Frequent Contributor
timestamp: May 13, 2024, 12:45:41 pm
content: Quote from: NiHaoMike on May 13, 2024, 04:39:39 amSorry, you give me the impression that you are not replying to my very last post.A 24V/1A SMPS (rated from 100 to 240 Vac for its input) supplies the controller board of a 220V-50Hz mains stabilizer (its mains input could be from 80V to 350V while its ouput is 220V +/- 15V).So, the added circuit (under the discussion here) should help this SMPS to work properly for a wider range of mains voltage (from 75 to 400 Vac, much wider than its rated range).