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  • EEVblog #139 – Let’s Select a DC-DC Boost Converter

    Posted on January 17th, 2011 EEVblog 57 comments

    Join Dave on the search for a single cell to 500mA 5V DC DC boost converter chip.
    What will he find?, and how long will it take him?
    What is the Maxim Datasheet FAIL he uncovers along the way?

    (Yes, it’s over an hour long, because that’s how long searching for this stuff takes, in fact I condensed it greatly already. Complaints can be sent to [email protected])

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    • John

      Wow. You should consider selling these lectures on DVD for educational purpose, might make a buck or two out of that!

      Oh and btw, the alkaline discharge curve you drew forgot to factor the current in: you get graphs like that with only light loads like quarter amp. With several amps the gentle slope is lacking and voltage just drops off the cliff like this (picture courtesy of Google Image Search):

      http://img.photobucket.com/albums/v482/SilverFoxCPF/IKEA1500AAatVariousRates.gif

    • R. Clark

      Dave,

      Nope, I made a stupid mistake with the first try at the simulation, so that’s invalid. A re-run shows that it could deliver 350mA at 5v at a 1.25v input with an efficiency of 85%, and 80% at 1.1v input.

      The stupid mistake that I made with the 500mA simulation was in not closely watching the outout voltage sag off at higher output currents as the input voltage became lower.

      In the simulation, the device continues to supply the full 500mA current rather than shutting itself off when the output voltage gets out of spec, so the voltage falls to 4.x volts as the battery ages.

      At high currents, it would need a shutoff signal applied to the SHDN pin so as not to send too low a voltage to the electronics. Even at 350mA, the output voltage drops to 4.x volts at 1.0v input.

    • robert

      This one was really tedious to watch Mr. Jones. I fear the “uncondensed” version would be subject to a “War Weapons Control Act” of some sort.

      I just had to skip to the end after having watched about half of it. Only to find out that you were still digging into data sheets…

      I was considering to check the validity of the given email, but refrained from it.

      What about multi-phase boost converters? They sound quite interesting. LT has some chips that can do just that. Much less input current ripple, smaller output filter caps, more juice…

      • http://www.eevblog.com EEVblog

        This one was really tedious to watch Mr. Jones.

        Bingo, that’s the whole point. This kind of process IS tedious.

    • Fritz

      When you are finding it really hard to find a way to do something it is often because what you are trying to do is dumb or impossible. I would have been leaning towards that conclusion after the first 30 minutes, but, I/we are not privy to your exact requirements.

      You are going to kill an AA cell very quickly. A Duracell Coppertop AA on 1W load gives about 1.1Ah to 0.8v with average voltage of around 1.15v. So about 1.15Wh. But you are talking about 2.5W out with grotty efficiency so it will be much much worse, if you can make it work at all I would be surprised if an AA cell lasts 10 minutes. Maybe 10 minutes is long enough for you, maybe those fancy expensive high power alkalines would do a bit better.

      • http://www.eevblog.com EEVblog

        Correct, you are not privy to what it is I am trying to do, and it may sound a bit dumb on the surface when you don’t know what is trying to be achieved.
        Yes, it is going to kill the AA cell very quickly, and do it very inefficiently, I know that.
        Yes, the lithium AA cells would perform a LOT better.

        • Wartex

          USB or cellphone charger. It’s pretty obvious. Mintyboost already accomplishes this by using 2x AA cells.

          1 AA at 3 amps will get super hot and die within minutes. I think application is irrelevant at this point because chip efficiency is irrelevant because your cell can’t produce the currents you want efficiently.

        • Fritz

          But 10 minute battery life is dumb in the vast majority of applications (the only <10 minute batteries I have come across were powering torpedoes).

          My point is that when you have trouble finding a solution you should question your problem and when you know your problem is 'dumb' you should expect to have trouble finding a solution.

          IMO in the blog you seem too surprised and disappointed when you kept not finding solutions.

          • http://www.eevblog.com EEVblog

            I fully understand your point. I suspected it wasn’t going to be easy from the get-go.
            BTW, the requirements of powering from a single AA and being able to find a 2.5W converter with low input V are mutually exclusive.
            I’m always a bit disappointed when I don’t find the ideal solution in a hurry, aren’t you?
            I am fully aware of the problems and the various solutions available for my particular application, I know perfectly well what I’m trying to do and why.
            Just because you can’t envisage an application where this would be required, does not mean others haven’t got a particular need.

            • Fritz

              Heh, if I don’t expect to find a solution I am not disappointed when I don’t.

              It isn’t just me not envisaging an application, if the semi manufactures had (with enough volume and not impossible) they would have made a chip for you.

              Anyhow good luck with it.

    • http://PrintPage-Justgotmynewmultimeter...thefamilybecome... Old-boewo

      Hallo friends

      for FLUKE Multimeter 8022A
      PartPicture: MP11 504324 89536 or
      FLUKE Stock No.453100
      Mfg Sply Code 89536

      For the above my meter I need a replacement display, who knows one that is not of FLUKE and fit? I need the LCD display, who has an idea and can help me who knows an LCD for Fluke which is another manufacturer?

    • http://electronicsdesigner.blogspot.com/ Mike

      Don’t cut it, an hour is fine! If they don’t want to watch and learn, that’s their problem!

      I set myself a challenge at the start of the video – to see how close I could get to your choice. In an hour I got nowhere near! I got a couple of LT devices that were close, and some Maxim devices that were similar, but I discounted them as they were Maxim (I only ever use them for small product runs).

      You should be able to get the final choice in spec if you do a little work on finding a better Schottky diode. The one specified is ok, but times move on and a little less voltage drop and better conductance should move the performance from marginal into a definite *tick* on the spec sheet.

      It was an excellent example to choose, it really does take hours of messing around on manufacturers and suppliers sites to get even close to what you need sometimes. Digging out the data sheet gotchas, the trade-offs and filling in the blanks. You know what’s really stupid though? I actually like doing it!

      There really is no hope for me is there ;)

      • http://www.eevblog.com EEVblog

        Interesting exercise Mike, didn’t expect anyone to do that and try and “compete”!
        Good (for me) to see you couldn’t get close in the same amount of time!
        Yes, I expected to cop a fair bit of slack on this video for it being too “long”. People know my usual response to that…

    • http://cidadao.uni.cc Mario

      Awesome!
      Im studying power electronics right now, I have an exam next tuesday. In particular Im solving an exercice about a buck/boost converter. I just made a break to see whats new on my “google reader” and there you are talking about dc/dc converters for more than an hour! eheh

      Also, few time ago, and for the first time, I had to choose an appropriate dc/dc converter for a portable device Im developing in the university and it was a pain… There are so many choices that it wasn’t easy to select the “best one”. I took a TPS63001 from TI and until now Im happy with that. But I wish I had seen this video before it, it would be a lot easier! :-)

      Thanks for all your videos. I really appreciate them!

      Cheers from Portugal

    • Jason

      Interesting, but at the same time so very, very boring and tedious.

      Oh and what’s with the smiley face at the bottom of the comment page.

      • http://www.eevblog.com EEVblog

        Interesting, but at the same time so very, very boring and tedious.

        Congratulations, you just learned that searching through datasheets to find a suitable part can be boring and tedious.
        You’re welcome.

    • PelleMannen

      Make a Joule Thief:
      http://www.youtube.com/watch?v=gTAqGKt64WM
      (however it works.. with just 1 transistor, 1 resistor, and 1 ferit inductor/transform thing)

      Made simulations of this circuit that enabled it to generate 10.000V in 1/10s (from a 1.5V batteri).

    • Drone

      I enjoyed this. It wasn’t too long. I let it run and listened – glancing at the screen when necessary to see the graphs. It was fun feeling your pain Dave.

      Show this video to an aspiring EE and they’ll end up in another major.

      Imagine being stuck in a tiny cubicle having to do this with product managers and marketing goons hovering over you asking if it’s done yet. Now imagine having to do that for the rest of your life :-(

      When I was a young Engineer we had a big data book library at work. Make a video of that part search process and I’ll kill myself.

      • http://www.eevblog.com EEVblog

        Sometimes it’s painful when you are under the pump to produce, but generally I like doing stuff like this, sometimes even “just for fun”, because it forces you to look at many different parts you never would otherwise have looked at. That knowledge might then be of some use for another project.

    • Greg G.

      You mentioned several times doing further testing on the part you decide upon. What’s the prefered method for prototyping with SMD components?

      I’ve had bad experiences trying to use expensive breakout boards with high pin count devices. If you are using something with a higher pin count than something like this DC/DC converter would you just bite the bullet and order a full prototype board?

      • http://www.eevblog.com EEVblog

        Universal SMD proto boards are popular, the ones with many different footprints that cater for a wide range of chips.
        “Dead bug” is another popular technique.
        In this case I wouldn’t do a full proto PCB unless I had hacked the circuit up somehow and got some basic measurements first.

    • Jay

      I liked the length. It was appropriate, considering that you were basically trying to find a part that didn’t exist. ;-) In doing that, you showed different ways that specific products had to be eliminated, how to interpret datasheets, use of both the distributors’ and manufacturers’ search functions, etc. It *was* tedious, and it’s probably only when we’re searching for parts for our own designs that it becomes “fun”. I’ve spent countless hours doing what you showed, and I’ve never been bored by it. It’s complicated, tedious, enjoyable, frustrating, fun, and in the end, hopefully very rewarding! But not always. :)

      About the Mouser search, I’ve found on various occasions that both Mouser and Digi-Key have some weak areas like the one you showed for the DC converter search. Some people swear by Digi-Key’s search, some prefer Mouser’s, but if you run into a problem with either, try the other one.

    • Henry

      This is precisely the function of those $US5 celphone single cell chargers available in every supermarket. Good news: They work. They appear to use a three-pin white LED driver chip and a few other parts to do the job cheaply. Reasonably efficient (I measured 65%) Bad news: They don’t work well at cold temperatures, they deliver at most about 250mA, transfer about 20% of the battery’s 2000mAh capacity (at these high currents), and the two different chargers I tested kept that up for about 30 mins before the battery was used up. I ended up using it at much lower currents (10mA/5V for an AVR project) and in a warm room, which was pretty much perfect. And cheap.

    • Tim Hoeppner

      Hey Dave,

      I really enjoyed this blog and it got me thinking about one comment you made. On your particular application you said noise didn’t really matter for your DC-DC converter. Hopefully this question isn’t too general but I’m wondering what type of situations you can think of where the noise would be a big issue?

      • Alexander

        Hi Tim,

        you could possibly interfere with an radio receiver. For example, the german DCF77 longwave time signal which transmits at 77.5khz. If your switching regulator is operating at 77.5khz too, then you might have a problem with the receiver getting nothing but noise.

      • http://www.eevblog.com EEVblog

        As a general answer, almost anything that involves something analog. It’s not uncommon for example to have to power ADC’s with their own local (and possibly power wasteful) low noise linear regulator, because any switching regulator would have too much noise for the job.

    • http://apexys-toan.blogspot.com/ apex

      Good tutorial,
      but why won’t you do it with an external switch?
      I mean, 16$ for just the switching converter is massive!
      apex

    • Hans

      A great video. The length may be long for some, but that maybe tells more about their attention span to subjects. I found out myself at this internship that finding the right part can take ages.

      What suprised me is that you only selected Step Up (boost) converter as type converter. Why not all the other type of converters that have boost in it? Some IC’s can function as multiple setups like you described with the MC34063.

      • http://www.eevblog.com EEVblog

        I did much more searching than shown in the video.

    • Erik

      About LTC3425, burst mode operation is a low power mode used to save power at low loads. That is why it has so low values. But I can’t find any good figures for normal operation. The next graph does have an indication of its capabilities at lower input voltages. The maximum start up voltage is 1.6V with an output of 5V and 500mA, which is better than MAX1703.

    • Neil

      Dave,

      I will confess – I was relieved when you has so much trouble with a reasonably simple requirement.
      I was just reamed by my boss for having spent a week trying to find a chip for an application fly-back converter. Worse – Company policy requires multiple sources (manufacturer) so the TI chip that does what I want can’t be used cos no one else produces a pin for pin equivalent. That is before we start talking about the transformer.

      Neil

    • Andy

      I hate to say that I got a bit bored with that one. It’s not an application that I’ve ever thought about in detail, but I got to the point about 20 mins in, where I could see *why* you weren’t able to find the part you were looking for.

      I don’t mind what you do or don’t know, but I was disappointed because I fast forwarded to the end, and found you saying, “suck it and see”.

      That’s a shame.

      There comes a point where you have to ask yourself “Are there other ways to achieve the end?”.

      That’s I guess the message I was hoping to see, and was sad about.

      One of the really serious takeaways, is that the cycle you demonstrated (for whatever reason) is not uncommon in the workplace.

      There can be much pressure to make progress, but unless there is time to stop and think, one may not see what is staring one in the face.

      Perhaps that is the true story of “Power Management”.

      :)

      • http://www.eevblog.com EEVblog

        You often have to “suck it and see” with things like this, especially devices like converters where there are often many factors involved to get the performance you require.
        But I eventually DID find a chip that looks like it will do what I want, subject to some real-world testing, I call that a win. So you are wrong, totally wrong.

        For the last time, I did ask myself “is there a batter way to do what I want”, but from the video you are not in possession of all the relevant facts to understand what and why. I can assure you that I knew EXACTLY what I was doing and why. It was not a futile search.

        For all those who said it was “boring”, “too long” etc, then the video was obviously not aimed at you, get over it. Some people really enjoyed it and “got it”, and that’s good enough for me.

        • Andy

          I’m now struggling to understand how I can be wrong?

          I never said “it was boring”… I said “I was bored”. I’m sure I wasn’t wrong about that. Actually it would be pretty hard to be wrong about that.

          So I was wrong to be disappointed?

          I’d be disappointed in myself, if I didn’t try to solve a problem more than one way, especially if intuition was telling me the problem didn’t want to be solved that way.

          Like a fireman’s pole. The fire guys kept falling down the stairs when the alarm rang. Then they weren’t able to attend the fire.

          The authorities, they said that the greasy pole was unsafe… Who’d have thought it?

          Are you saying that you don’t search for parts with more than one scheme in mind?

          That’s why I was disappointed.

          Stairs… they’ve always worked. They might be a bit steep for this fire-house, but let’s suck it and see?

          Try as you might, you can’t blame me for not understanding something you didn’t put in the vid. Perhaps I wouldn’t have got bored if you had.

          What I guess I was trying to do, was to exercise my feeling. I might have done this in a natural way; the hope of understanding what I missed, that caused it to seem boring.

          I conclude: I suppose it must just have been a boring one!

          • http://www.eevblog.com EEVblog

            I’m now struggling to understand how I can be wrong?

            You are wrong because you (like others) implied that my search was futile, that I didn’t find what I was after, and/or that I didn’t think about other ways to do the design, and generally had not put much thought into it.

            It has nothing to do with your comment about you being bored. If you were bored, that’s your problem I’m afraid, not mine. A video can’t be all things to all people, it’s impossible.

            Are you saying that you don’t search for parts with more than one scheme in mind?

            No, not at all. In fact in this case I WAS searching for a part with more than one scheme in mind.
            I don’t put every last minute detail into my video blogs explaining every single thought in my head and every design process and all the reasoning. If I did then they’d be twice as long and I’d get twice as many complaints, and then I’d STILL get people interpreting things the way I didn’t intend anyway, so it’s futile.
            But no, I don’t blame you or anyone else for interpreting things the way you see it, that happens with almost every video I do.

            • Andy

              Oh, I see….

              EEVBlog is going the way of Jeri whassup with the blobby Mams. We get to watch you work!

              Dave mate… (Fosters Moment)

              You ‘aint got no mams.

              :rofl:

      • http://www.eevblog.com EEVblog

        One of the really serious takeaways, is that the cycle you demonstrated (for whatever reason) is not uncommon in the workplace.

        And THAT’S what I was intending to show, nothing more.
        People have asked to see that exact cycle I use (however boring it is), using the Digikey and the manufacturers sites etc, and that’s who I did the video for.
        Those who wanted the in’s and out’s of designing a product and circuit and it’s requirements from the ground up and detailing all the design decisions and reasoning would have been disappointed. Sorry, but that’s just tough, it wasn’t for you, and it lacked much detail in that area.

        Please understand that I get complaints of one form or another for EVERY video, and that adds up to a lot of complaints, and it does piss me off sometimes. I debate whether or not to even reply to anyone at all.

    • wardenclyffe

      I wish it were longer.

      • http://www.eevblog.com EEVblog

        I wish it were longer.

        As usual, I can’t win either way!

    • PedroV

      Hi Dave! Battery Tutorial, Battery Tutorial, Battery Tutorial! ! ! That would be really cool! Nice the way you found those errors on the maxim datasheet. Has you say, traps for young players.. Cheers

    • Drone

      Dave, It is Great that you continue to monitor an respond to the comments on this post.

      Parts search is at least half the time spent on design – at least in my experience these days. More time spent searching for the right part results in saved time at the bench prototyping. Alas, gone are the days when you knew the the applications (not sales) Engineers on a first name basis and could work with them on the telephone. But let’s not forget, the Internet enables us too, especially with price control.

      How about a blog post (or many) detailing and/or comparing distributor and manufacturer sites and how they help (or hinder) the search for a “few” common part types? (“Common” parts is the keyword here; otherwise methinks it gets out of control).

      I know this is a BIG challenge, but well worth it IMHO. It will at-least bring to light the many shortcomings of search that plague us. It may also bring you law suits :-(

      Tear apart the likes of Mouser, Digi-Key, Farnell-Newark etc. when it comes to Distributors and the biggies in terms of manufacturers.

      Go for it Dave… Take ‘em on!

    • Pingback: Electronics-Lab.com Blog » Blog Archive » Let’s Select a DC-DC Boost Converter

    • Ondre

      Nice one, Dave!
      Next time my chief askes me what I did for the last couple of hours, I’ll just send him a link to this video ;-)
      Anyway, still wondering what Dave’s super secret project might possibly be. Is it a battery powered battery charger?

    • Pingback: Let’s Select a DC-DC Boost Converter – Robo-X

    • Dave C

      Another excellent video Dave. Thanks. Here are a couple of minor comments I had from watching it:

      1. When looking for parts on Digi-Key, Mouser, etc., I’ve found that I get better results when I *don’t* use the keyword search feature. The problem is that if you search for a particular keyword or phrase, even if it seems very generic, you may end up excluding products that by chance don’t happen to have those exact keywords in their description.

      The search shown in the video, “DC converter” was actually fine, because the category for these parts has both of those keywords in it, which means every product in that category also implicitly has those keywords associated with it in Digi-Key’s search engine. But in general this may not be the case.

      E.g. if you search for “DAC”, you will find 10,179 items in the “Data Acquisition – Digital to Analog Converters” category (which is the main category for DACs). If instead you browse to that category (with no keyword search active), you will see 10,800 items listed. So the keyword search eliminated 621 perfectly good parts.

      I do use the keyword search feature to figure out which categories are of interest, and in some cases to refine a parametric search (e.g. to search for “audio” while browsing DACs).

      2. I think you’re overestimating the power output of a AA alkaline, and the minimum input voltage for your converter. The internal resistance of a brand new AA alkaline cell is around 200 mohms, and it goes up as the cell is discharged (see http://data.energizer.com/PDFs/alkaline_appman.pdf ). If my math is correct, assuming an 80% efficient converter, I think that limits you to ~2.5w output with a fresh battery, dropping down to about 0.5w when the battery reaches 1.1v (open circuit). Vin to the converter will go from 0.8v with a fresh battery down to 0.55v at the end.

    • What name did I use last time?

      Oh well. Hilarious how the instant gratification crowd is out in force. If there isn’t an explosion or some LED lighting within the first two minutes in the video they get bored.

    • E-Hybrid

      First off: You’ve done a great job again, Dave!

      ::.About the length issue.
      1.) I think without your expedient chatter and stop-page explanation the whole search process would have taken on video maybe 40min (give take). But I’m sure it would have been less informative.
      2.) From an educational stand point you have done a wonderful job demonstrating how, literally “FUCKED UP”, these component searches can be. I hate step-up boost converters, because it’s not just a pain in the ass, its utterly insane – try making 5 tones out of 1 tone of gold – good luck! I think the time was well spent for every aspiring EE, because for those without the patience to build good electronics this was certainly a scare video and for those who have the patience it is surely a resuring video of the horrors to come and the higher job-availability on the market because all the bored hick-ups dont pester themselves with details!

      ::.Thoughts on the search process.
      Watching your video I really thougth: Heck, why cant all these major and minor manufucks just open a common database for all their components. But then I thought, Hell, Digi-Key and Mouser do just that (extremly poorly as shown in the video: NOT all components are listed and the datasheets are WRONG!!!)

      As a GERMAN I have the native need inside of me to make things efficient. Truely we GERMANS are culturally obsessed with the idea of Efficiency and Structure (as we have sadly proven in the past with high processing gas chambers for Jews – a very bad example for our cultural qualities – I have a very sarcastic humor – DONT COPY!).

      These Datasheet screw-ups really get me! How utterly mindfucked must they be? Dont they recheck their work before publishing? Hell, humans are failures – Yes! – Thats why we build mashines to substitute for our Abomination!

      Anyways, I really really wished some manufuck would (maybe digi-key, etc.) come up with the brilliance to host a java or something dynamic based database with the datasheet not just being a boring pdf, but kind of a database in itself where I dont need to hope for the author to put in the right diagram for what I’m looking for, but could extracts it as needed from a sweep spectrum of test results they made. Yes, even measuring at 0,2Vin test results, you could extract from such a datasheet!

      The most logical action (as Vulcans would say) would be to eradicate the Human idiotism from this universe!

      Hell, I love your videos Dave! Please continue. Your comments are highly opinionative (which is fucked up awesome) but at the same time highly informative.

      You have again achieved what you aimed for. A horribly accurate and interesting video on how the component mary-go-round wastes a vast amount of my valuable life-time (at least I think it to be valuable).

      I enjoyed it and anyone who doesnt isnt a EE to the core! I hope Darwinism sorts you out so I get next year a better paycheck due to the lack of EEs on the job market!

      Greets from Germany!

      P.S.: I dont know the specs of your project. Sounds superficially retarded what you are trying to do, but my first thougth was, that you might be inventing a smart fire-and-forget bullet weapon or missile or something like that. ^^

      Would you be so kind a share with your viral and evergrowing addicted community WHAT THE HELL YOU ARE BUILDING?! =D

      • E-Hybrid

        Additional Thoughts:

        A.) I would love to see you and that AfroTec guy collaborate somehow. His prescript abilities and your elaborate time-consuming conversational uttering would be one hell of a show in my imaginative world somewhere distributed in the space of my prefrontal cortex and signal transmitting juices up in my head.

        B.) I am nearly sure one of those components you ruled out due to the lack of an appropriate performance diagram would have done the job. This criticism would support my idea of a dynamic and interactive datasheet document format (open-source off course) – provided, that the DATA provided, is providingly proper and accurate providededededede…

        ERROR 319b – please restart program.
        //…

        ———————————————-

        • http://www.whatameter.com Jeff Weinmann

          Dave,

          I love all the armchair quarterbacking that goes on after a great video like this.

          The best comment was the battery being drained after 10 minutes.

          This whole “what’s the point” attitude just kills me.

          I’m working on my own project that will monitor water usage remotely.

          I already got a couple responses like : “why would you want to do that, your meter tells you already how much you are using…”

          Then I say ok, if you can monitor your water remotely say, from a vacation spot, and one of your water pipe bursts, instead of coming home to a flooded house you could be warned as soon as it happens…

          Many people just want to hear themselves, how they ‘debunked’ the great Dave Jones, etc.

          Great segment I thought I agree with the first comment – you could sell this to a university as a lecture segment. “EEVBLOG Lecture series now on DVD or Blueray – Just $39.95!”

    • http://none Dirk

      I watched the whole show and enjoyed every minute of it.

      Now what does that make me? :)

    • Mav

      Well I enjoyed it , although I am all too familiar with the process.

      Those who say it’s pointless or bad design , too long are to my eyes missing the point on two counts.

      1) The biggest of the two and the one Dave has taken undeserved flac for is that its a stupid goal. Unless you know what the application is your not in a position to say if it is stupid or not.

      2)This is exactly the process you have to go through for each and every IC choice in your design, and I think that’s what Dave was trying to demonstrate and as he said if he’d posted the extensive search he no doubt did then the vid would be triple length.

      Infact it could have been longer and some points Dave missed are also critical to my eyes.

      Product life span is one. You can go through all this component selection rigmarole over the span of a larger project only to find that when it gets close to production time the components you sourced are no longer available and there is another bite in the ass, back to square one.

      Another is you can source a close enough product and design your system only to find further down the design route and infinatley better solution by another manufacturer (better function , cheaper BOM ect) crops up and you find yourself redesigning X chunk of the circuit.

      This doesn’t cover half the gotchas , but to cover them all would be near impossible.

    • Dave

      Dave,

      Nice job – your videos are excellent and informative. I realize the point of this video, as you’ve already mentioned, was to show how lengthy and complicated the process of component selection can be (and how easy it is to get fooled). However, I can’t resist letting you know that you passed over the LTC3425 too quickly – it’s the part for this job (and considerably cheaper than the other part you chose). Unfortunately, the datasheet didn’t provide the curve you were looking for to show its capabilities. This is primarily because there are so many possible Vin and Vout combinations, the graphs get too busy and hard to read, so manufacturers tend to show the ones that are most likely. Not many people want 5V @ 500mA from a single cell because of the short battery life that would result. However, if you looked at the Vout=3.3V curve, you would see that this part is capable of supplying a full 1A of output current at 80% efficiency from a 1.2V input. It can, in fact, provide the 5V output you’re looking for.

      Again, nice work.

      P.S. No – I’m not an LTC marketing guy, but I might know the designer of the ‘3425 ;-)

      • http://www.eevblog.com EEVblog

        Any curve at Vout=3.3V has no direct correlation for 5V output operation, that’s why they give you curves at different voltage, because they can and almost always are very (often drastically) different. If you did try and extrapolate, you’d get a theoretical 0.66A @ 5V which is fine and dandy, but it’s not going to do that, it will be less. How much less? you’d have to do some measurements to find out.

        • Dave

          Actually, as you explained at the beginning of your video, there is a fundamental relationship between output current and input current, based on the ratio of Vin and Vout (which makes the 3.3V data somewhat useful as a predictor of 5V capability). In any case, with a guaranteed input current limit of 5A min, the LTC3425 should be able to provide well above 500mA at 5V with a 1.2V input, even with efficiency losses taken into account. I happened to take this data today, using Linear’s LTC3425 demo board. With an input voltage of 1.2V (well decoupled) and an output voltage of 5V, the LTC3425 was able to supply not only 500mA with 81% efficiency, it was able to supply up to 800mA before hitting current limit (with an efficiency of about 68%). Note that this is with a stiff lab supply; with an actual battery as a source, and its attendant internal resistance, the input voltage would likely drop too far before reaching this much current, but that’s a different discussion!

    • Laichh

      One thing to share: at the last column of the Digikey result table, you’ll find the link to the manufacturer’s datasheet. This way you don’t have to enter the selected device page for the datasheet. ^_^…

    • http://www.toddfun.com Todd Harrison

      Dave,
      I noticed for the part you picked the date/rev at the top of the datasheet was Nov-1998. Has that boost converter really been around since 1998 and unchanged?
      Todd

    • Nate

      I beg you to become a professor and do video series on circuits 1-2, electronics, and embedded….ect for beginning engineering students.

      I’m from the USA at NDSU university and most of the professors here are.. well… simply trash. They are hired for their ability to make money with research as opposed to their ability to teach. Furthermore the majority of them can barley speak english. This is commonly reflected across many big EE colleges in the USA.

      In many of my preliminary classes over half the class would simply drop out or fail due to utter frustration with the learning process of electrical engineering. Most of what i’ve learned about electronics has been from http://www.youtube.com/user/MIT, Wikipedia and from work.

      However, when explained clearly, electronics and EE is not that difficult of a concept. There is no reason it should be such a pain to learn this stuff. Anyhow, thanks alot for your videos and hope to see some more of them!