**The Ultimate Guide to SEPIC Converters: A Detailed Explanation**

Are you familiar with the versatile and efficient SEPIC converter? If not, this article is perfect for you! In this detailed explanation, we'll dive into the world of SEPIC converters, exploring their unique features, working principles, and applications.

**What are SEPIC Converters?**

SEPIC (Single-Ended Primary Inductor Converter) converters are a type of DC-DC converter that uses a single inductor to provide both boost and buck functions. They're designed to be efficient, compact, and relatively easy to implement.

**How Do SEPIC Converters Work?**

A SEPIC converter works by using a single inductor (L1) to store energy during the switching cycle. The inductor is connected to the input voltage source and the output capacitor. During the boost phase, the MOSFET switches on, charging the inductor with the input voltage. During the buck phase, the MOSFET switches off, allowing the stored energy to be transferred to the output capacitor.

**Why Are SEPIC Converters Popular?**

SEPIC converters are popular due to their high efficiency, compact size, and relatively low cost. They're widely used in various applications, including power supplies, battery chargers, and DC-DC converters for industrial and medical equipment.

**Can a Single Inductor be Used Instead of Two?**

Yes, a single inductor can be used instead of two, resulting in reduced AC current losses. This modification is said to increase the efficiency of the SEPIC converter. However, this might not always be feasible or practical, especially when working with existing commercial designs.

**Efficiency Improvement: Can Couple Inductors Make a Difference?**

To practically check whether coupled inductors make a noticeable difference, one can desolder the original inductors and measure their values. If desired, new coupled inductors with similar values can be created or purchased. In this article, we've experimented with winding our own coupled inductor around a toroid core and reusing a 100uh power inductor.

**Results: Does Using Couple Inductors Really Make a Difference?**

Yes, using couple inductors did make a difference! After modifying the SEPIC converter, we measured an increase in efficiency of up to 4%. However, this difference might not always be significant enough for manufacturers to bother implementing it, as coupled inductors are more expensive.

**Conclusion: Is Building Your Own SEPIC Converter Worth It?**

If you're looking to create a high-frequency voltage converter with low noise and decent efficiency, designing your own SEPIC converter around the TL494 PWM controller IC can be a great learning experience. However, building a high-frequency voltage converter on a perfboard might not be the most practical or efficient approach.

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WEBVTTKind: captionsLanguage: enI love DC voltage converters like these andso should you.I mean you can get them inexpensively fromsites like Amazon or Ebay and they are oftentimes crucial when it comes to powering yourelectronics projects.For example a Buck Converter takes a higherinput voltage and converts it efficientlyinto a stable lower one while a Boost Convertertakes a lower input voltage and converts itinto a higher one.And if you got a variable input voltage thatchanges over time then you can simply getyourself a Buck Boost converter which likesthe names implies can work as a buck or boostconverter and thus delivers a stable outputvoltage no matter what you got on the input.That is why Buck Boost converters are in myopinion the most versatile ones.But here is a little secret you might notknow and that is that pretty much all smallcommercial buck boost converters you findon the internet that come with two coils arein fact so called SEPIC converters aka SingleEnded Primary Inductor Converters.I know that term sounds complicated but ina nutshell it is just a special voltage convertercircuit topology that actually does not requiretwo coils to function properly.It could theoretically also work with onephysical coil that comes with two windingsbut you never see such designs on Amazon orsimilar.Soooo is using one coil instead of two a secrethack that lets this converter work even better?Well; we will find out in this video in whichI will not only show you why the SEPIC converteris so versatile and epic, but also try outthe coil modification and even build a DIYversion which you might want to build at home.Let's get started!This video is sponsored by JLCPCB who offer3D printing service for $1 and PCBs with freeassembly for $2.Currently they are working on more SMT capabilitiesbecause they are preparing to launch a standardPCBA service; so definitely stay tuned forthat.But until then feel free to try out theirawesome quality PCBs that you can receivewithin a week of waiting.To kick things off I got myself three kindsof commercial SEPIC converters which all camewith slight variations concerning their usedcontrollers, inductor values and so on.And if you are asking yourself right now whyI am so sure that those are truly SEPIC convertersand not like maybe an inverting Buck Boostconverter about which I told you all aboutin a previous video; then let me tell youthat I actually desoldered the componentsfrom one of them in order to reverse engineerthe PCB and thus create this schematic forit.And I think everyone can agree that it ispretty much identical to the SEPIC schematicsyou can find on the internet.With that out of the way let's firstly answerthe question how this thing works and don'tbe scared it is not rocket science becausethere is really only one switch that can eitherbe opened or closed.So let's imagine the switch was just openand now it is getting closed.But what is noteworthy is that while the switchwas open the capacitors here in the middleand at the end got charged up.Now with the switch being closed, currentflows and rises almost linear through inductor1 because it is building up its magnetic field.While that is going on the middle capacitordischarges itself through inductor 2 whosecurrent flow also rises linear because itis also building up a magnetic field.And while those two inductors are basicallystoring energy, the output capacitor suppliesthe load with current and thus keeps the outputvoltage stable.This goes on for specific amount of time whichis of course defined by the frequency andduty cycle of a square wave signal appliedto the MOSFET that pretty much always actsas the switching element in such a circuit.And as soon as the signal changes from highto low, the MOSFET turns off and the inductorspump the energy from their magnetic fieldsin the form of current through the circuitto the load while of course charging up theoutput capacitor and capacitor in the middle.Then the control signal once again changesto high and this whole cycle repeats.Now by closing the switch for a longer timeand thus increasing the duty cycle, we canbasically vary how much energy we pump tothe output side and therefore create a variablevoltage on the output.But please don't think that you can easilycreate super high voltage high power outputsthis way.Because as you would expect the amount ofenergy you can transfer depends on a wholelot more than just the duty cycle like theinductor, capacitor and diode parameters aswell as the switching frequency.To learn more about definitely check out thelinks I put in the video description.But anyway this SEPIC converter topology isso popular because it does not come with invertedoutputs like a certain other buck boost converter,it comes with a good efficiency, its outputcan be completely shut off, its short circuitbehavior does not result in complete destructionof the converter unlike some others becausethe input and output sides are coupled bya capacitor and finally its MOSFET positionand overall control feedback operation isthe same as with a boost converter which meansyou can simply take an off the shelve boostconverter control IC and easily build thisthing.And now that we understand how the converterworks and why it is pretty EPIC; let's getback to the one inductor instead of two inductorsquestion and to answer that we can simplyhave a look at the voltage drops across the2 inductors.As it turns out the voltages across them arethe same in both switching positions whichmeans you could wind both coils onto the samecore, call it a couple inductor and the circuitshould still function the same while apparentlyreducing AC current losses meaning this modificationshould increase the efficiency.And by the way I had to double check thisfact as well because this is no longer somethingyou can easily spot.But anyway to practically check whether coupledinductors make a noticeable difference I firstlyhad to determine the efficiency of one ofmy commercial SEPIC converters.So at an input voltage of 12V and an outputvoltage of 5V it came with an efficiency between72 to 62% which is OK I guess.Next I desoldered its inductors and measuredthem to find out that they came with all ofthese beautiful values at a frequency of 52kHzwhich is by the way the frequency this specificcontroller IC uses.Now at this point I tried finding a commercialcoupled inductor with similar values but ohboy that was certainly not an easy task andthus I eventually gave up on that.So what I did instead was firstly windingmy own coupled inductor around a toroid corewho was not designed for this but in the endfeatured really promising values.And my second idea was to simply reuse this100uh power inductor that you can get forcheap from the internet.As you can see one winding consist of 4 wiresso by separating them and finding out whichone is which we can create two strands andthus get the 4 wires we need for the coupledinductor design.So I soldered those wires to the PCB accordingto how the schematic demands it shown by thosetwo little points.And after the first power up I was very happyto find out that the theory was in fact correctbecause everything still worked like usual.And after once again measuring a couple ofinput and output power values I was also happyto find out that the efficiency did in factincrease by around 2 – 4%.Now using the other DIY coil initially didn'twork quite right but eventually it decidedto cooperate and with it I achieved an evenhigher efficiency.So does that mean that using couple inductorsis a secret hack?Well, not really because I cheated by creatingway bigger DIY coils in comparison to thecommercial coils.But if we trust other experts who createdthis graph then we can see that there is definitelya slight improvement with coupled inductors.Only problem is that this difference is solittle that most manufacturers do not botherbecause coupled inductors are simply moreexpensive.And that basically solves my initial questionmeaning you can get yourself such a commercialSEPIC converter without hesitation.And If you are not sure which one to get thenI would recommend this one since its buildon MOSFET comes with a very low resistanceand thus it guarantees the highest efficiencycompared to the SEPIC converter we modifiedbefore and the one which is build around theXL6009 controller IC.Now while looking at those efficiencies Ieven thought about taking on the challengeof creating my own DIY SEPIC converter thatwould be more efficient but as it turns outbuilding a high frequency voltage converteron a perfboard results in a ton of noise whichmakes it pretty much unusable even while onlydrawing 1A of current.But on the other hand designing a circuitaround the TL494 PWM controller IC was reallyeducational and fun.So here is my final schematic in case someonewants to give it a shot or improve the designbecause as you can see it does in fact workcreating a variable output voltage between2.5 and 20V DC.And with that being said you should now definitelybe familiar with the SEPIC converter and thushopefully learned something new.If so consider supporting me through Patreon.Don't forget to like, share, subscribe andhit the notification bell.Stay creative and I will see you next time.