Categories
Podcast

Shhh, Don’t Tell The Aussie…

I know we said we wouldn’t talk about it on our sites any more, but I figured once more can’t hurt. We have our latest episode of The Amp Hour up on the new website, just waiting to be downloaded or streamed.

I will say though that you should pull the RSS feed ASAP in order to not miss any future radio shows. Who knows what kind of hijinks you’d miss out on?

Anyway, don’t tell the Aussie! I don’t want to upset my co-host. But do remember to shoot over to The Amp Hour for the 4th installment of the new radio show and leave some nice comments there.

Categories
Part Review

Part Review: LT4180

A note about part reviews: I do not get paid to do reviews. I am either doing them out of the kindness of my heart, because they have some historical significance (as in the case of my review of the LM741) or most likely I think the technology is important and interesting. All opinions are my own and I would not suggest making any part choices based on the information in this article alone. Read some datasheets, they’re pretty informative.

No wire is perfect.

Basically, that’s the premise behind this chip, the LT4180. The real background is that when someone is providing power to a remote device they want the voltage to be accurate.

An example of this might be a USB supply to a device more than 20 feet away. The host (whatever is in charge of setting up communication and providing power, such as a computer) is supposed to supply 5V to the device (such as a printer or a mouse). In this case let’s assume that the device is very dependent on that voltage being correct, for one reason or another. The real problem is that the wire providing that power has some innate resistance to it.  Even a resistance of 1 ohm at 500 mA (the max current of USB) can cause a drop of .5V. That’s 10% of the intended voltage!

So what are the traditional options? Well, the best one is to have a separate set of wires known as “sense” wires. They detect the voltage directly at the device without drawing much current (likely by utilizing high input impedance op amps).  So the current that is powering the remote device will be sourced through one set of wires and the voltage at the device will be fed back to the whatever is supplying the voltage. In theory if the resistance of the wire changes (due to temperature, stress, etc), the controller will react and adjust the voltage up or down so the correct voltage is delivered to the device.

But what if you already ran your wires and you can’t run a second set to sense the remote voltage? You either design in a regulator on the device side (a good idea regardless) and source a higher voltage or you just design in devices that can handle a large swing of voltages. Neither is the best idea, though they are likely to be cheaper than using this part. At $3 minimum price you’re much more likely to find a cheapo linear regulator which you can put on the device end and then burn power there. You lose efficiency but gain a few points with the MBAs in your company.

Enter the LT4180. You can put this device in line with a voltage regulator, as shown on page 6 of this wonderful app note.

As a quick aside, you know LT cares about this product as Bob Dobkin, the co-founder and Chief Technology Officer at Linear, co-wrote the app note. Very cool, you don’t see high level execs getting their hands in on the action very often these days.  I was impressed at least.

Back to the app note itself, you’ll see that there is a switching regulator or linear regulator that is providing the initial voltage. Then this device sits between the voltage regulator and the wires that lead out to the device. Notice also that there are only two wires, a source wire and a return wire.

Now for the magic. It has two key pieces, explained in better detail in the app note, but summarized here.

The Dither — LT calls it an algorithm, but in effect they are only stepping the supply current up and down by 5%. So if the initial regulated current is 1A, they step it up to 1.05 A and then down to .95 A (similar to what is shown below with a different timescale). Why? Because it’s effectively forcing an AC (varying waveform) through what was a DC (non-varying) channel.

Doing so allows you to gather the impedance of the channel without directly measuring the drop due to the resistance in the wires that are sourcing current. According to the app note:

Because C is sized to produce an “AC short” at the square wave frequency, the interrogating voltage square wave produced at the power supply is equal to VSUPPLY(AC) = 0.1 × IDC × R, measured in Vpp. The voltage square wave measured at the power supply has a peak-to-peak amplitude equal to one tenth the DC wiring drop. This is not an estimate—it is a direct measurement of the voltage drop across the wiring over all load currents.

As illustrated below, the AC square wave is now shunted to ground instead of going to the load. This is how you can be certain it’s the actual resistance of the channel and not the channel AND the load. How cool is that?

The Control — Wait a second, how do they do that when they are not a part of the switching regulator or linear regulator? Nor does the regulator have any control lines with SPI or I2C or similar? LT illustrates 2 ways, but the basic idea is the LT4180 feeds back an analog voltage to the controller. This can then be used in myriad ways. The most straightforward way is to feed this voltage back to an error amplifier on the regulator, if it has one. The error amp will interpret any incoming signal as an error and correct the output. By dithering this signal by a little in either direction, the output current from the regulator can be made to vary. Other methods shown include feeding the signal into the trim circuitry (that controls the precise voltage allowed by certain regulators) or even feeding it into a discrete MOSFET based current source. With the voltage feedback signal there are certainly a lot of creative ways to feed this information back to your regulator/switcher to achieve the desired dither.

All in all, I was impressed by this part. I haven’t had it on my bench yet to try it out, but the idea alone made it intriguing enough to write about. Power is a really big market and growing and Linear Tech makes no secret of the fact that they are targeting the more obscure but lucrative problems such as this one.  I’d like to reiterate that the app note is fantastic for this part and the datasheet fills in technical details and specifications that aren’t in the app note. Hopefully I made what was already well written a little easier for others to comprehend on the first pass.

For people that have landed on this page from Google, I would prefer that you do not ask any design questions, I am not actively using this part and I’m sure there are many others out there that would serve you better. For everyone else, if you have any questions, please leave them in the comments. Thanks for reading!

Categories
Analog Electronics Engineering Learning

Follow Up Post: Electronics People Online

I really don’t have much to say in response to my last post about where all the electrical engineer sites are online other than: message boards. I alluded to the idea of message boards when I mentioned EEVBlog, though unknowningly at the time; I thought EEVblog was only videos. Working with Dave on The Amp Hour has shown me that a message board can really help hash out ideas (if you’re one of the content generators), get suggestions, or get questions answered (if you’re watching or reading and don’t understand something).  So I started hunting and found some other quite active electronics-only forums:

  • All About Circuits Forum — The main site is a great online open-source textbook that explains lots of electronics concepts.
  • Electro-Tech-Online — This is an intense amount of posts, namely about electronics.
  • Eng-Tips — This is actually a site for all types of engineering but the link is for the electronics part of the site.
  • EEVBlog Forum — Like I mentioned above, this is Dave’s forum and it has some great chatter going on it.

Then there are the hacker/maker/DIYer type forums. These often span multiple disciplines and include questions from people who may have never seen a resistor before but you can usually find some good answers (or answer some questions yourself if you are so inclined).

  • Instructables Community – Not limited to electronics but there are enough electronics projects that there are forums about it.
  • MAKE forums — Hard to find a bigger group of DIYers than MAKE and you know they’re bound to have questions for one another (or you!).
  • Hacked Gadget Forum — Alan’s site is usually a great aggregation of new, fun hacks that are popping up on the web; but the forums are a good place to ask about them!

Vendors often get in on the action as well. Why not? You buy the parts or kits there, you should be able to ask questions to others you KNOW are using the same things, right?

  • Adafruit Forum — Great way to ask about their popular kits. I’m disappointed they don’t sell the RF jammers that LadyAda designed though.
  • Sparkfun — The biggest hobbyist kit manufacturer out there, with over $12 million in revenue per year. With those kinds of numbers, you know people are hanging out at their site (even when they’re NOT giving away $100 of free stuff in a day). More people = more questions = more answers for you.
  • Parallax Forums — A kit maker that utilizes the BASIC Stamp chipset. When you can’t ask the Arduino heads about your issues, you’re going to need a forum to talk to.
  • Element 14 — They are a sub-company of Farnell, one of the largest distributors of components in the world. There’s extra useful content now that they own EAGLE (the CAD program)…but you can find some good general answers there as well.

There are also more specific types of forums out there, which makes a lot of sense. You wouldn’t care about working on precision op amps if you have a question about how to get an Arduino to control a relay.

  • DIY Drones — Want to know how to make a quadcopter? I bet this is a good place to ask about it.
  • AVR Freaks — Talking about AVR (the chipset in the Arduino) can get very specific. These members will help you with your specific questions.
  • Society of Robots — All things robotics, including the electronics needed for them.
  • DIY Audio Forums — High end audio electronics, built by you. Talk to others on the board to figure out if the sound is “warm” enough.

The thing is, even though I like the tailored nature of a message board (ask a question, get an answer), I’ve never really thought of them as a place for electronics people to congregate online. I was quite wrong though. The message board system is democratic in nature because those with the most involvement and the best answers will rise to the top as experts (though I like the StackOverflow/Chiphacker style for this better). Aside from the democratic nature, there can be contrasting voices in case there is a wrong equation or a better way to execute a design; this is important for checking engineering ego and ensuring a design will work properly. I think most of all though, it’s easy: easy for the website creator to set up and easy for people to understand how they work. All of these factors point to a pooling of collective electronic resources online.

So if you’ve never tried it out, give a message board a shot! You can find some great information, connect with some really smart people and maybe help one or two others as well. And if you find any not mentioned here, let us know in the comments.

Categories
Podcast

Same Show, Same Time, Different Location

We finished recording the 3rd installment of our newly-named radio show–“The Amp Hour”–last night. The show focused on a couple different topics, we were trying to stay a little bit more focused than we had been previously. Anyway, be sure to click the link above to get to the podcast/radio show, I don’t plan on putting the audio on this page anymore. I would also suggest that you try out the RSS feed on The Amp Hour, it’s the easiest way to get up to date info on the program; plus I’d like to discontinue posting that there is a new episode up on both that site and this one.

Speaking of this site, I realize there hasn’t been much writing lately as I’ve kind of sidetracked into the audio side of things. If I was being completely honest, I’d say it’s easier to just spout what I think about a subject than to sit down and write out a coherent article. But I really plan to get back into that in the near future. The theme is finished for the new site, we’re all set up to stream or feed podcast readers and our show content seems to kind of evolve over the course of the week. All this hopefully points to me having a little more time for writing about analog and random other things. Thanks for hanging in there, if you happen to be.

Categories
Podcast

Radio Show Has Moved!

Dave and I have decided to move the radio show we started together to a separate site. We also chose a name for the site, The Amp Hour.

Going to a different site will allow Dave to continue providing video podcasts on the EEVblog site and I can continue providing analog type articles (and podcasts) on this site.  Our content will appear there from now on, but we’ll be sure to link over to that site for the next few shows to ensure people know where the audio files can be found.

While I’m sure I’ll miss all the traffic working with Dave has brought to this site, I’m really excited about continuing this project and getting more listeners to The Amp Hour.  Pop on over to The Amp Hour to catch the past two episodes of the show or grab the RSS feed so you know when we post our next one (usually at the beginning of the week).

Categories
Podcast

2nd Radio Show With Dave Jones of EEVBlog

Dave and I have recorded our second radio show. Still no name for the show, or else it would be posted at a different site than this one.  If this show happens to inspire an idea for you, please leave your idea in the comments.

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Links discussed in the show:

We would love any feedback either in the comments or at the EEVblog forum (there is a specific section for the radio show).