I like it when I understand things. The universe feels like a little safer place, even if I realize feeling secure is only a state of mind. And when I watched Steven Chu talk on the Daily Show the other night, I felt safer. Not like a warm security blanket kind of safe. More like a “Hey, if stuff hits the fan, we’ll probably be able to figure it out” kind of safe.

How many times have you looked at a government official and said “Hey, they seem pretty bright!”? How about “What a great sense of humor and perspective for the situation we’re in.”? How many times have you honestly said in the past 8, 16, 20 or 28 years have you really looked at a government official and said “Hey, I bet he has science and the earth’s best interest ahead of a corporation that is whispering in his ear.”? Not too many at all.

I’m not saying that there have been scores of corrupt politicians in the past Presidents’ cabinets, because there haven’t; the people advising the President are often capable and well tempered in their decision making. I’m also not saying Steven Chu will be completely successful in the political arena, as it’s a very different world from what he’s used to. It’s just so damn refreshing to see such an accomplished scientist in a position to influence legislation, all the while weighing facts and data instead of political usefulness and opinion. Give me more politicians like him and I’ll start to feel that the government has turned a corner.

So thank you, Steven Chu. You’ve restored my hope that we can get some more renewable energy initiatives moving instead of just talked about in this country. You’ve restored my hope that renewables might be able to help pull our country out of a recession. And from what I know about you and your plans, you’ve only just begun.

Also the requisite thank you to Comedy Central and Jon Stewart for interviewing him. Without you, I’d only get biased news from biased news sources

A background

Switching regulator, buck converter, boost converter, SEPIC, flyback, push-pull, buck-boost… do you know what the heck these things are??? Because I sure didn’t when I was getting back into analog electronics. Now thanks to new interest in power efficient electronics, they are starting to come front and center on the electronics stage. Hopefully this article will give you a better understanding of what they are, what they do, where to use them and issues with noise.

OK, so before we get to the real topic of this post, what do switching regulators do?

Switching  regulators allow you to translate one voltage into another. They allow you to take a higher voltage and translate it to a lower voltage or a lower voltage and go to a higher voltage.

“Eureka!” you cry, “Chris has found the solution to all of our energy needs! We just hook a bunch of these switching doo-dads up and we’ll have unlimited power!”

But no, it’s not that easy. Switching regulators go off the fact that you can take a voltage and translate it to a different voltage, however, the power stays the same (in an ideal case). Meaning if you have 5V coming into a circuit and you have a portion of that circuit that needs to operate off of a 15V supply, you can use a boost converter or something similar and crank up the voltage. Say you have 150 mA (at 5V) coming in, when you convert it up to 15 V, you’ll have 50 mA available to whatever needs the 15V power. Notice in this (ideal) case, the power stays the same (750 mW).

It is a similar story when going down  in voltage. However, there are many more options when moving down in voltage: switching regulator, linear regulator or even a passive element (like a resistor or a diode). You use a switching regulator because they regulate the output voltage (unlike the voltage drop across a resistor or a diode) and they don’t waste power like a linear regulator. If you want to go from a 20 V input down to a 5V output, a linear regulator would just “burn” up that 15V in the middle. With a switching regulator, most of the power is conserved (assuming you are running in the optimized voltage ranges…and there are a ton of different models to choose from so you can find the right range).

Finally, real quick, where are these used? Well, the hot new talk of the town has been renewable energy. “I can get 95% efficiency?” you ask, “Why wouldn’t I pay $4 per chip to do that?”. And really, the power efficiency isn’t just the garbage everyone seems to be spewing these days about saving energy for savings sake…it actually can help you make a better product. If you are in a heat sensitive situation, you don’t want to use a linear regulator to get your required voltage. In the above example if you are going from 100 mA at 20V and the output of the linear regulator is 100mA at 5V…that means you are burning 1.5W just regulating your voltages. With a switching regulator you can save a good percentage of that (for battery or “green” devices) and you can reduce the heat in a sensitive application. Plus, if you’re trying to go from a lower voltage to a higher voltage, you’re out of luck with linear regulators.

Switching Noise

Nothing in life is perfect. Switching regulators aren’t 100% efficient, there are limits to how much you can convert voltages (1000v down to 10V usually isn’t possible…or smart) and even in the best cases a switching regulator will introduce noise into a circuit. For the ways I have mostly used switching regulators (supplies for digital circuits), switching noise isn’t that big of a deal. If you are supplying 5V to a piece of flash memory, the part will probably not care if there is 100 mV of noise “on top” of the 5V signal (meaning the actual power supplied would bounce between 4.9V and 5.1V). Same for supplying power to LEDs or other non-analog situations. However, if there are any measurement components in your design or any even slightly sensitive analog portions, you should consider how the switching noise will affect your output.

So why does switching noise occur? To answer that we really need to look at a switching regulator to understand what is inside of it. To illustrate, I will be using my version of LTSpice, which is free (awesome!). Also to note, there are lots of great programs out there to help you design this stuff (Webench, for example). Just don’t want to leave any of the vendors out, especially when they give out sampled parts. For this example, we’ll look at the LT3755, which EDN (and me by extension) showcased in an article about creating simple LED lighting for your home.  The application here would be to boost an input of 10V to an output of 40V to light an array of up to 14 1A LEDs.

Notice the LEDs (D2 in the diagram) are where the final current and voltage is being delivered. The waveform for the inputs and outputs is below:

In this graph we see the voltage at the point above R4 (the sense resistor), which is close to what is being delivered to the LEDs. Notice that the voltage starts at roughly 15V and then shoots up to around 40V; the “on” state when the LEDs would be lit settles around 38V. When the red PWM waveform turns off, the voltage bounces up to the exact voltage (40V) the LT3755 is supposed to be outputting because the LEDs are not draining on the output of the circuit. When the PWM goes back on (to 5V), there is noticeable noise on the output voltage. So why is there noise?

If you look at the circuit diagram above, the second most critical component after the regulator itself is the inductor (L1), just to the upper right of the LT3755. Switchers take advantage of the fact that the voltage across an inductor is equal to the instantaneous current through an inductor times a constant (known as inductance). Pulsing current through the inductor introduces the voltages necessary to step the output voltage up to the desired level. Using negative feedback, the controlling chips can output pulses at varying speeds and shapes to correct for any errors on the output of the circuit (see the image above to see the current going through the inductor in light blue). However, as stated before, nothing is perfect. The bandwidth of the chip (the op-amps and other controlling elements within the chip) are finite, so there cannot be perfect control. This introduces noise on the output of the circuit at the same frequency as the switcher (and some harmonics of that frequency).  In the LT3755, the switching frequency can be anywhere from 100 kHz to 1 MHz.

If you are using this switcher for LEDs in a car…no big deal. And really, with high power applications such as lighting, the noise isn’t much of an issue. However, as switching regulators find their way into more and more products, the noise issue becomes more prevalent, especially smaller products. The trade-off comes in when you start looking at the inductor required for the switching regulator. Some can get quite large and unwieldy, especially for handheld products (see below for an unwieldy example).

So instead of using a large value (and size and price) inductor, the switching frequency needs to increase. As explained before, voltage is created across an inductor by forcing pulses of current through the inductor. The higher frequency means that there are smaller current pulses, but there are more of them. This allows for smaller and smaller inductors in designs (some are starting to be pulled into the chip packaging!) but brings with it the noise, now at a higher frequency.  If you have a 5V power supply line with 100 mV of noise of top of it (with the noise at around 100 kHz), then it might not be a problem on your circuit board. But when your boss tells you to start using smaller parts so you can fit the design in a handheld form factor and the switching frequency goes up to 1 and 2 MHz, you will start having problems. That innocent 100 mV from before now might couple into other board traces and introduce noise into the rest of your design. If you have any analog signals that are critical to your design, 100 mV of noise can wreak havoc on the output.

Less noise, more answers

Switching noise is something that will be apparent in any design involving a switching regulator. Knowing your system constraints will allow you to best decide which option is best for your specific needs. If you are crunched for space, you will need to be able to handle high frequency switching noise. If you are sensitive to noise, you better buck up for some big, expensive inductors and carefully route your board (in fact, if you’re that sensitive, maybe reconsider switching regulators entirely). If you have access to the resource, the best people to ask are the vendors selling the parts; they know the funny behavior of a part and which “flavor” of regulator to use to best suit your needs. And in the meantime you can play around with the tools they make available online and in software.

Please leave any questions or comments you might have and good luck with your new designs!

Hi everyone,

I know there aren’t too many concerned blog citizens out there, but I just wanted to post to say I am taking the rest of the month off from writing to take care of personal stuff (mostly my house). I would highly suggest you leave any blog post ideas you would like to see when I get back on the “skribit” widget on the right side of the page. Alternately, you can vote on suggestions that are already there. I get weekly updates on which post ideas are popular and will use those to build up my post repertoire in order of popularity (most of the time). Thanks for reading, as always, and I look forward to continuing the conversation about analog electronics and renewable energy when I get back.

~Chris Gammell

I like the communication between myself and my readers and my readers (either random or regular) on the comments section. As such, I’ve decided to try some posts titled “What the world needs” (similar to the “My Hobby” posts over at xkcd). These will supplement, not supplant, my regular posts. So here we go:

What the world needs, part 1…

What the world needs is more energy storage solutions. What we have right now just isn’t going to work. Batteries aren’t reliable enough over the long term, ultracapacitors aren’t developed enough and large scale solutions just aren’t efficient enough. All we keep hearing about at the Detroit auto show are the hybrid and plug-in vehicles (Nov 2010 for the Volt? It’s going to take that long??). While they have the conversion from braking energy back into stored energy, I feel like all of the stored energy solutions right now (within the cars, just are not sufficient). Furthermore, when all those plug-in vehicles are in the driveways of the suburbs and sucking down grid power, there will be a higher need to draw upon reserves of energy, either by cranking on more power plant capacity or tapping stored energy. If we want renewable energy to fill that gap in available power we will need even more storage capability, as renewable sources are not “always on”.

My favorite idea out there is the storage of energy by pumping water up a hill (known as Pumped Storage Hydroelectricity); it’s so simple and beautiful, basically you pump water up a hill and then release it later to be converted through turbines into electricity. The initial concept was developed to help deal with load variations on power lines but also to help sell lower cost electricity produced at night during the high cost hours of the day (a concept the plug-in vehicles also hope to capitalize on). Today we see these hydroelectric storage facilities being targeted as ways to store energy from sources such as solar cells or wind turbines.When the sun isn’t shining and the wind isn’t blowing, renewable sources cannot output power; people do not typically stop consuming energy during those times though, quite the opposite. When the sun is highest A/C units are cranked and when the wind is blowing outside people are cuddled under blankets watching TV or reading by lamp.

Like any engineering problem there are limitations. Evaporation reduces the efficiency in arid climates where large photo voltaic installations are likely. Wind occurs more naturally and is more likely to be harvested in areas with out large inclines to pump the water up and down. The turbines are not 100% efficient so there are losses during any pumping of the water. So the question remains, how else can we store and then harvest energy to take advantage of renewable energy infrastructure?

1. As the verbiage above suggests, we can actually store energy and harvest it through biofuels; it’s really just a different way of thinking about an existing solution. Corn is a favorite right now, with switchgrass being a potential in the future. Mother nature helps us take sunshine, nutrients from the soil and water to produce plants that can be converted into energy through distillation.
2. Gravity (in non water forms) could help us store more energy. I think of having lifts that could raise large weights into the air to be released at later times. I know there’s a lamp that uses gravity to temporarily light up LEDs, but I wonder how scalable this idea is.
3. Spring energy has always fascinated me, ever since I got one of those wind up planes as a kid (you turn the propeller to twist a rubber band which then releases to unwind the propeller as the plane flies). I imagine a huge spring being pushed by some weight and then slowly released later to power a generator, but I doubt the materials would allow this indefinitely (springs eventually lose their “springiness”).
4. Heat is another storage mechanism but has some serious limitations. You could try and heat up a medium (salt? water? saltwater? I think I saw that somewhere), but then maintaining the heat and retrieving it later provide some serious issues.
5. Hydrogen is touted as a great storage mechanism; while I like the fact that water is readily available, I don’t think the storage capabilities are reasonable. One of the things I like most about the pumped storage facilities is its simplicity.
6. Pumping air into a bladder or bag underwater could be a possibility someday. You would pump air into the bag and once the pumping had stopped and you wanted to retrieve the energy, the pressure surrounding the bag would force the air back upwards; when you need it, you direct the air through a turbine to retrieve the energy. Temperature changes as you go down in depth would be a concern (air compresses as it gets colder).
7. Batteries are still an option…basically taking electrons and squirreling them away into electrolytic solutions (or however you want to do it). These become severely limited in large scale operations though; imagine how many “AA” rechargeable batteries you would need to store the output of a 500 MW wind farm…

As a final note, I should point out I found this other Wikipedia article on grid energy storage at the end of writing this post. I still wanted to publish my ideas but only some of them matched.

I get a little frustrated when I try and think of new ways to store energy; however, it’s reassuring that there are many options out there that can still be improved upon. Can you think of any other natural or otherwise methods of storing energy? Let me know in the comments!

Photo by obenson

I glanced at my natural gas bill today while cleaning up the house and was a little shocked at myself. I pride myself on being better than most on conservation (at least cognizant of it) and my usage was quite high. That was last month and I can only imagine this month will get worse. And yes, I do live in a rental house right now (with an energy efficient house in my near future), but that’s the case for a lot of people, especially lower income. So I got to thinking, what will stop people from using so much energy in their frosty, great northern homes?

The answer is, of course, money. It always has been. But now we’re in a climate where the costs are beginning to rise so fast that people who sat dormant before will begin to take action. In fact, this will also likely move people in all economic groups to take action; the most important of these being the middle- to lower-income groups. Why? Because costs like heating are a larger percentage so there will be a more voluminous cry from the masses for cheaper energy (not that we don’t love our green friends, pushing the renewable energy agenda and buying recycled elephant dung paper as Christmas gifts for family). Hopefully more people clamoring for energy efficient devices and alternative fuels will push us towards a tipping point (which I incorrectly identified as a singularity), where renewables become the norm and cost of energy will drop due to the abundance of natural energy, waiting to be converted. So as prices continue to increase–and the temporary drop in gas prices is undoubtedly temporary–the push from most people will be towards a more sustainable future.

How about you? Have you felt the need to push for more conservation lately solely on energy costs? Let me know in the comments.

Photo by nothern green pixie