international standard for ac/ac converter ("electronic transformer") - Page 1
Forum section: electronics / projects

author: poorchava
author_rank: Super Contributor
timestamp: June 25, 2020, 11:16:41 am
content: Just a simple smps-based converter to step down 230V to 110V, for the life of me I can't find it on the IEC website.

author: ArthurDent
author_rank: Super Contributor
timestamp: June 26, 2020, 01:05:32 am
content: If you're trying to convert 230VAC at 50Hz to 110VAC at 50Hz, that won't be that simple or cheap to accomplish electronically and a transformer/autotransformer would be far more practical.

author: bin_liu
author_rank: Contributor
timestamp: June 26, 2020, 03:29:14 am
content: The transformer/autotransformer is very bulky, and the SMPS is very lightweight. Many Chinese companies manufacture this kind of equipment, and also design and produce car Inverter. What I know is that these products look for some loopholes and use ordinary Electronic products EMI, EMC, CE... standards for certification.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 26, 2020, 04:02:42 am
content: How many amps and what kind of load? That would hugely impact what sort of solution would be the best.

author: poorchava
author_rank: Super Contributor
timestamp: June 26, 2020, 07:08:03 am
content: The solution is gonna be an AC-buck topology running probably at around 40kHz (or higher if the inductor becomes too bulky) with bidirectional switches (either 2x mosfet or diode bridge + igbt) + requisite filtering to pass the emissions. We're talking about 150W output power. It's probably not even gonna be regulated - fixed PWM because the equipment can handle mains variationsIt must be SMPS because of size, weight and cost.I am only looking for the requisite standard to design to (such as 60335 for white goods and 60730 for building automation)

author: Siwastaja
author_rank: Super Contributor
timestamp: June 26, 2020, 07:39:24 am
content: What you are asking for is a chicken-egg problem.While it'stechnically possibleto revolutionize AC/AC with SMPS, driving size, weight and also cost down, just like AC/DC did approximately during 1990 to early 2000's, what you ask for iseven more complexthan AC/DC was, and the economy of scales isn't playing well, because it's needed in much smaller numbers than AC/DC conversion.So forget cost as a factor. Depending on number of units, it's going to end up between 10x to 100000x more expensive than the bulky transformer. Of course, unless you do it as a hobby/learning project, in which case you could forget about any standards, as well, right?Large inverters do exist in power distribution systems, but I guess it's too different from what you require for a small plug-in product.Sorry I don't know about the standards. The fact you can't find one means it's a real possibility it's such a special corner case niche that there is no direct standard for what you are asking. Then you need to think about which standards are closest.

author: poorchava
author_rank: Super Contributor
timestamp: June 26, 2020, 10:09:19 am
content: well, this does not have to be isolated, nor does it have to have stellar sine wave shape (just enough to pass emc/thd/blablabla).LTSpice tells me, that this is gonna work (see attachment).I have also done this in a fan motor controller, just without the LC on the output, as the motor does not need it.As far as I can tell a classical toroidal 150...200VA trafo will run about 40€. I don't see any problem in manufacturing that thing from spice diagram + filtering and some simple transformer-based gate drive for approx. half of that.I mean, maybe I'm wrong, but I can't see any technical reason why a simple solution jaki this wouldn't work.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 26, 2020, 01:40:50 pm
content: You could rectify the incoming AC into a center tapped pair of capacitors, then half bridge switch the load with respect to the center tap.

author: poorchava
author_rank: Super Contributor
timestamp: June 26, 2020, 01:48:06 pm
content: Why would I do that?

author: schmitt trigger
author_rank: Super Contributor
timestamp: June 26, 2020, 02:14:31 pm
content: In a company I used to work some years ago, we had a similar device.But it made sense because it would also change the frequency in addition to the voltage: 120V, 60 Hz to 230V, 50 Hz.It was powering some European made equipment.But nowadays almost everything is universal voltage and frequency.

author: poorchava
author_rank: Super Contributor
timestamp: June 26, 2020, 02:22:50 pm
content: The scenario is that a potential customer is importing some battery powered equipment (dunno exactly, think a hedge trimmer or something like that) that has a charger which is supposed to work ok 110V. Dunno how it's built inside. Redoing the charger as a whole is outa question due to proprietary battery socket and cost.I know that it will work, it's also easy to get right in terms of not blowing up. I also have a few years of experience in power electronics, but mainly high power (single digits kW range) DC/DC stuff for test equipment market.I wonder however what would be the point of rectifying splitcapping the supply. The capacitors would have to be significantly large.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: June 26, 2020, 03:35:44 pm
content: Hi,The schematic is this:The output waveform is:The regulation for the values given:This circuit needs an inrush limiter, NTC or similar.Jay_Diddy_B

author: poorchava
author_rank: Super Contributor
timestamp: June 26, 2020, 05:14:21 pm
content: That makes sense. Much easier. I wonder how the power factor on this one is gonna be. It seems that everything non-lighting over 75W is required to have a good power factor. This one will probably have around 0.7 or something.The chopper solution just chops the input, so should automatically have a good PF.The chopper will introduce quite a lot of noise and harmonics though.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: June 26, 2020, 09:17:49 pm
content: Hi,The power factor is really quite low, around 0.4 for resistive loads.If is already has a bad power factor, for example a SMPS with no PFC, the PF will be approximately the original PF/2.This is because the current waveform is the same and the input voltage is double.This is based on the idea thatPF = W/VA for non-sinusoidal load currents.PF= cos (angle) only works for sinusoidal load currents.This solution is only suitable for light loads.The electrolytic capacitors can be chosen based on the load. Start with 20uF per Watt of load dissipation.Regards,Jay_Diddy_B

author: poorchava
author_rank: Super Contributor
timestamp: June 26, 2020, 09:36:40 pm
content: We're talking about 150W here, that would translate to about 2x 3000uf @ 200V caps. Not exactly small not cheap nor light.IiRC 560uF@400V is something like 35x58mm. So 3000u@200v would be something like 1.5...2 times as big.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 26, 2020, 11:07:41 pm
content: Quote from: poorchava on June 26, 2020, 02:22:50 pmSo basically switching power supplies. First check the label - a lot of stuff is universal voltage nowadays. If it's 120V only, the half bridge trick can use much smaller capacitors by increasing the switching frequency to 400Hz or so.

author: wizard69
author_rank: Super Contributor
timestamp: June 27, 2020, 07:10:18 am
content: QuoteGive the customer a GPS coordinate to the nearest hardware store. This wouldn't be the first time that I see an engineering effort put into an already solved problem.In the off chance this isn't a hedge trimmer there are numerous companies that make equipment specifically for this problem. This includes huge motor generator sets that can power entire production lines to plug in travel transformers for shavers.

author: ch_scr
author_rank: Frequent Contributor
timestamp: June 27, 2020, 02:02:23 pm
content: Quote from: Jay_Diddy_B on June 26, 2020, 03:35:44 pmSadly this circuit does not work. Once the caps are charged up, the AC across the load goes away. There is no load across the DC.