Transformer LLC Half Bridge resonant converter  - Page 1
Forum section: electronics / projects

author: Whotheman
author_rank: Newbie
timestamp: October 10, 2021, 01:13:53 pm
content: Hello, in a little project, I rectified 230 V 50 Hz to 320 V DC an want to use a LLC Halfbridge resonant converter, to convert the 320 V to 100 - 400 V.Any recommendations for the transformer? Switching frequency will be (due to IGBT‘s in the half bridge) Around 10 kHz to 40 kHz.I did not find ready wounded transformers for a case like this but maybe you know a product or manufacturer. Thanks!

author: sandalcandal
author_rank: Unknown
timestamp: October 10, 2021, 02:13:40 pm
content: Wurth has some decent off-the-shelf transformers which are made for small LLC power supplies.https://www.we-online.com/catalog/en/WE-LLCRThey're rated for a higher frequency than your target but that shouldn't cause issues as long as you can find one with high enough inductance for your needs.Not particularly cheap but ok if this it's just a "little project" where you need one-offs.Designing and winding your own transformers is another option but that's quite a learning curve.

author: moffy
author_rank: Super Contributor
timestamp: October 10, 2021, 06:32:22 pm
content: LLC's are not very good for wide ranging output voltages, they can only cope with a fairly narrow range of variability. Perhaps another topology would be better suited? Depends very much on the power range. You'll notice that for the Wurth transformers, they quote a narrow 360v-400v input for a given output voltage say 48v.

author: Whotheman
author_rank: Newbie
timestamp: October 11, 2021, 05:15:16 am
content: Thanks for reply. Würth seems like no option because of the small secondary voltage. Mine has to be between 100-400 V regulated through the duty cycle. So maybe winding my own transformer is the only option?@moffy the design should be for about 600 W.What other topologies would you recommend?

author: moffy
author_rank: Super Contributor
timestamp: October 11, 2021, 05:30:03 am
content: Quite a common topology at that power rating is the push/pull using the venerable SG3524 chip. Lots of the power supplies you can buy, 240v to say 48v DC at 480w etc are based on this circuit. But the variation from 100v to 400v is going to be tricky. You normally use the PWM to cope with load current variations and a certain degree of voltage variation, but with such a large variation the magnetics will get complicated unless you just heavily oversize the main transformer etc.

author: jonpaul
author_rank: Super Contributor
timestamp: October 11, 2021, 06:10:31 am
content: Bonjour a tous just saw this now, Welcome to the world of power electronics design!I was analog/power EE since 1968, I had designed many production converters in 1970s..1990s , medical, avionics, high voltage , lighting.The Metcal SP-200 solder station 500 kHz resonant design, was my design circa 1992.1/ IC: The 3524 was from Silicon General in 1976, an ancient controller. I recall a few issues but cannot be specific. Suggest to use a modern push pull driver instead.2/ Topology : The resonant converters with soft switching are normally used at much higher freq 100k..25 MHz. The higher freq reduces filter component size and magnetics sizes.At 600W I have used the double forward instead of half bridge, solves a few issues in half bridge.Nowadays even a Flyback or single forward at 600W is much simpler.3/ Power switch: IGBT limits the freq. and imposes some drive requirements. A well selected MOSFET will be fine.4/ Magnetics: No "off the shelf" transformer will drop into your specific application.Check The usual suppliers like CoilCraft, Bourns, EPCOS, Murata, Taiyo Yuden, TDK, perhaps not at 600W and your freq and output voltages.Beware, a stock catalog part may be on 6 mo backorder from China.5/ IF you want to learn a new field, suggest to research texts and sites on SMPS design and power magnetics. Mfg like TI have calculators and CAD for such and the old Magnetics Designer program is now free and open source. Many FET and contrôler IC mfg. wrote extensive app notes.6/ I would use a simple core and bobbin and wind by hand. Search "Ferrite cores" TDK, MHW and EPCOS sites. Material and gap will depend on final design frequency.Suggest core shape ETD and EER, avoid pot cores and square leg EE, EI.Find stock bobbins at Micrometals.Just the ramblings of an old retired EEENJOY AND LEARN!Jon

author: voltsandjolts
author_rank: Unknown
timestamp: October 11, 2021, 08:52:51 am
content: There is little information from the OP, more is required to specify the design.There is a 400W SG3525 half-bridge resonant converter (IGBT@25kHz, core E47/20/16@50kHz) on my desk with variable 10-400VDC output, but it's not regulating as such, it's just charging a capacitor bank to a set voltage, and so operates intermittently. What are you doing with the 100-400VDC and what are the regulation requirements? That determines the complexity of the design.

author: sandalcandal
author_rank: Unknown
timestamp: October 11, 2021, 11:48:11 am
content: Quote from: Whotheman on October 11, 2021, 05:15:16 amSorry didn't notice your voltage requirement. Configuring multiple transformers and their windings in series and parallel is an option to get flexible ratios and also increase power handling. Obviously there can be some drawbacks around size and cost (and parasitics to an extent). I've seen some cutting edge high power reference designs intentionally using magnetics split up across several cores to help with packaging and power dissipation.In this case you would probably put primaries in parallel and secondaries in series but since you need all the way up to 400V that might be impractical. Doing a back-to-back pri-sec-sec-pri could work but could pose some performance challenges due to parasitics piling up.As others have mentioned, there are plenty of decent and affordable (likely cheaper for the overall system) MOSFETs for your voltage range which will perform better than IGBTs so I also suggest you consider them.Edit: 600W is would also be too much for a single pair of the Wurth transformers. Would likely need 3 pairs which is again, a bit excessive. There are also these "flex transformers" with multiple 1:1 windings but I'm not sure the single winding voltage rating is sufficient (no single winding max voltage given)https://www.we-online.com/catalog/en/WE-FLEXHVYou would then also need a separate resonant inductor.

author: Boscoe
author_rank: Frequent Contributor
timestamp: October 11, 2021, 11:59:23 am
content: I don’t want to be that guy, but…600W alone is no trivial task, 600W at 400V is very dangerous. Using parts you have kicking around is not the way to go. In a previous work place an engineer was nearly blinded due to faulty chips exploding on a fully tested and verified high voltage design. High voltage isn’t just about electrocution, all the stakes are made higher.All in all I feel if you have to ask, you’re not ready for that sort of project. I recommend reading and trying low power low voltage stuff extensively before trying something like this.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 11, 2021, 03:03:45 pm
content: Also, conventional (square-pulsed) switching (flyback or forward topology; I'd probably prefer 2-switch flyback?) is perfectly acceptable at the stated power and voltage range, why complicate it with LLC?Tim

author: Whotheman
author_rank: Newbie
timestamp: October 11, 2021, 05:27:27 pm
content: Wow, did not expect that feedback with so much expertise. Thanks!Attached is my „functional schematic“ I already built the rectifier and I have a LLC evaluation board (a reason why I want to stick to the LLC topology ;-)).The purpose of the design is DBD (Dieelectric Barrier Discharge).MOSFETs to Substitute the IGBTs seems clear to me!I think I will wind my own Transformer and dive into the inductive world first of all.Thanks for your support and no worries, I will be very cautious in testing and running the Design!!

author: jonpaul
author_rank: Super Contributor
timestamp: October 12, 2021, 06:16:58 am
content: Rebonjour WhothemanYour new post about the application and block changes everything in your spec.We designed many such transformes and electrodes in 1990s for ozone water purification applications.Consider to first research deeper the field of DBD.What is your application, eg ozone generator?Dielectric Barrier Discharge requires high voltage and high frequency, and the electrodes present a highly capacitive load.The first problem is to characterize the load the DBD electrodes, so accurately measure capacitance at 50 kHz with the fluid or test material in place.The power will depend on the dielectric losses at that frequency and voltage.I think power is 10-50 W not the 600W mentioned.No off the shelf transformer can provide a 1;140 ratio with 40 kV output at 50 kHz.High voltage high frequency is a maximum stress on insulation and above 20 kV the transformer will generate ozone unless totally encapsulated or vacuum impregnated.HV windings are an art, especially at 40 kV/50 KHz!We normally use a sectionalized bobbin and production designs require universal winding, to reduce self capacitance. Vacuum varnish or special filled epoxy is needed to prevent breakdown and carbon tracking. Termination is not trivial.The system design block seems overly complex, for instance a class C oscillator could drive the transformer and electrodes.The "pulse" output is too vague especially since most DBD use a sine. Please exactly define the PRF, duty cycle, width, etc of the "pulse".With so many fundamental issues in your project, I would shelve the hardware design and first learn more about topics mentioned.To research high voltage transformer design and fabrication.A good reference is "Magnetic Components Design and Applications"by my old friend Steve SMITH 1984.https://www.amazon.com/Magnetic-Components-Applications-Steve-Smith/dp/0442203977An excellent ref from Finland:https://www.mv.helsinki.fi/home/tpaulin/Text/hveng.pdfFinally beware that HV HF can cause RF burns, destroy test equipment and burn up thick insulation.These devices are like Tesla Coils.Bon chance,Jon

author: Just_another_Dave
author_rank: Regular Contributor
timestamp: October 12, 2021, 09:37:09 am
content: Quote from: Boscoe on October 11, 2021, 11:59:23 amAt least he is not using GaN Mosfets, which can explode quite easily…As Boscoe suggest, I would start with a smaller design as a proof of concept if this is your first resonant converter or one based on a PWM topology if this is your first time working with power electronics. I’ve designed a couple of LLCs and I can say that at the specified voltage and nominal power many things can go wrong, especially if you haven’t simulated the transformer to check that it won’t catch fire (which is difficult with off-the-self ones as their datasheets don’t usually provide much information about them).Choosing a topology just because you have an evaluation board based on it is not the best way to go, as other ones might fit better your application while being easier to design. Most of them can be tested using standard lab equipment, just requiring a low frequency VNA to test the control loop (although this can also be achieved with an oscilloscope)