I'm working on a new switcher design and need to be able to test the total current coming out of a boost converter. Here's what I'm looking at:

• 0-60V rails (out of the boost converter)
• 0-350 mA
• No access to the load that will eventually be connected to the switcher

So what do I need? I need something that can sink current and dissipate any heat that will be generated. If the load is dropping the entire voltage at the top current, that will be:

This is quite a bit of power. I was using the TIP41A that I have on hand, a power NPN transistor in a TO-220 package. With this amount of power, a heatsink is most definitely required. Here's the simple circuit:

In this circuit, the divider from the incoming source (the top rail) sets the current going to the base () and this times the (in this case anywhere from 15-60) equals the current down through the collector (). This is not the optimal way to sink current from your source, but it's a start. The fact that I'm dialing in the current with a potentiometer in a divider that is also connected to the incoming load is not great, but again, this was a quick and dirty way to get up and running. But wait, you think that's a makeshift circuit? Check out my heatsink:

Yup, that's a crowbar.

Close up of the attached BJT

I didn't have any proper heatsinks laying around, so this became my hacked version. During testing, I was looking at 30V across the TIP41A and roughly 300 mA through it. The heat was transferred well from the TO-220 case to the crowbar and the dissipation was decent (heatsinks with fins are better at dissipating the heat). Next I need to step it up and see if this simple circuit can perform under full load. If there was perfect contact between the case and the crowbar, we should see roughly:

I wouldn't be putting my tongue on the crowbar anytime soon, but I think that's reasonable enough to handle this situation.

Now, there are much better ways to do this. I really like my co-host at The Amp Hour, Dave Jones' video about a programmable dummy load. Hell, he even has a legit heatsink! There are advantages to using a MOSFET over a BJT as well, but I went with a BJT for this situation. Mostly I was just giggly about using a crowbar and thought others might enjoy. So...hope you enjoyed! If not, check out Dave's video below:

I'm finally starting to get it.

Apparently in the past the design work I've been doing is too slow. It's too methodical, I have too much time to question my decisions. Well not anymore.

I've been working on a time sensitive project recently (sensitive enough that I feel bad writing this post at 9 pm on a  Saturday) and I've finally started to understand the reason the part vendors come to talk to me about power module this and fast design that. They come in with these nearly-done solutions and try pushing them on me, only to hear me say something like,  "Wow, I'd never use that". I mean, where is the fun in using a power switcher that is damn near complete?

But now that I'm in a situation where I feel the need. I feel the question rising in me..."WHERE IS IT?!"  I expect the answer, the part I've been looking for to be sitting in large quantities, in stock at Digikey. I figure I have a very simple, very common problem that needs to be solved not just by me, but by many other engineers the world over.

Honestly, I was looking for a completely integrated module that converts from a 24V bus voltage down to a 5V bus voltage to then be branched with various linear regulators. But there's nothing out there. No turnkey solution. No simple-as-hell solution. But I want it. I'm willing to pay for it.

And now finally I'm starting to see why they create modules with built in this or that. It's because there are tons of people out there like me, just trying to move on and get the job done. I'm not quite ready to pay the $20+ price tag certain vendors want, but I'm considering it.

So kudos to all those chip makers out there who recognized the need. But until you have exactly what I want, I'll be elbows deep in datasheets if you have a new part to show me.

"Wha?"

That's what you said when you read the title, isn't it? That's probably what I would have said. You said that for one of two reasons:

1. You've never watched Firefly.
2. You've watched Firefly and you just don't get it yet.

The second is more excusable than the first. If you've never watched Firefly, I highly suggest going to do that right now. It's 14 episodes (one season) and a feature length film. It's a great show that was unfortunately cancelled after one season.

"So what the hell Chris? You're sounding like a lame fan boy."

Yes, yes I am. And I loved the show but I love the analogy much more. So let me explain the background on Malcolm Reynolds a bit before I dive into the relevancy to this site and electrical engineering.

Malcolm Reynolds, played by Nathan Fillion

Mal was the captain and owner of the Firefly (a spaceship). Prior to that, he participated in a war between the Alliance and the Browncoats, on the losing side. After the war (and where the show picks up), he is working with a small crew, floating through space and picking up jobs wherever they can. They aren't always glamorous jobs but they often require ingenuity. Often times, they are avoiding the Alliance, which is a federation of the populated planets. They control just about everything in the galaxy and have very advanced technology. They seek to bring everything under their control.

Starting to see my point? I believe that engineers of the future (and already starting today), have only a couple options:

1. Be part of the ever growing "Alliance" -- In this case, the corporations (companies >200 people) that have an increasing share of the technological population.
2. Be part of a smaller company (20-200 people). However, I believe that over time these smaller companies will continue to disappear (in the electronics world) because of the difficulty of competing on cost. They will either go out of business, see costs increase to the point of employees leaving (healthcare premiums, anyone?) or will get swallowed up by bigger companies.
3. Work alone or in very small teams. Work on jobs for smaller companies in a contract situation. This would be where the future engineer is very similar to Malcolm Reynolds.

The corporations mentioned in the first point are large for many reasons, not all bad. One of the most striking is economies of scale; places like a semiconductor fabrication facility simply cannot operate with small budgets. They need capital equipment which is produced at great cost and the company is necessarily big in order to recoup the initial costs. Another is working with very advanced technologies. If you happen to be an engineer that is working with circuits that operate at 10's to 100's of GHz, you likely require very advanced equipment in order to monitor and modify your circuits. Only the largest companies will be able to afford the bleeding edge technology required to develop future technologies (i.e. If you're working on 20 GHz signals, you need a scope that can detect 40 GHz or more in order to see higher order effects). While in Firefly the Alliance wasn't necessarily big because of these reasons, they were very advanced technologically and were the only places that offered opportunities to work on the bleeding edge.

Now before I take this analogy too far, let me speak to the "stealing" side of Firefly. I think that's really where it begins to fall apart. Hopefully none of the engineers of the future are taking from the large corporations that represent the Alliance (except maybe the contracts they win). Stealing isn't right and in the show is usually because of necessity; I would never encourage any engineer to be anything but outstandingly ethical. However, there are situations in the show where the crew of the Firefly work indirectly for the Alliance in hard times, which I think is reasonable. In engineering terms, I imagine a small design firm of the future working on fixtures for a large factory that needs to outsource some work. Or working in conjunction on a project because the small team is a preferred vendor for a particular part of a product (the embedded system in a robot, for example) and the large corporation provides "the rest" (the remainder of the robot and the expensive moving parts, to continue the robot example). These are all plausible situations in the future and even happening today.

To compare engineers and engineering firms of the future to the Firefly crew paints kind of a bleak future (if the analogy is to be believed). It will be hard to find work because much of it will be dominated by larger companies. And why wouldn't it? The corporations offer more manpower, lower costs and the potential to create larger things. However, all is not lost. Smaller engineering groups can offer many things which also have parallels in the Firefly universe. These are lessons which can be used today and are a reason I liked the analogy so much. Let's go over how and why a smaller engineering crew might succeed.

1. The ability to take jobs that larger companies cannot or will not.
   • Large companies may not want to take on jobs that are small and do not provide a likely return on investment (ROI). However, a smaller company may be willing to gamble on these sorts of things. Historically, the smaller ideas have larger risks but much larger rewards, which could be beneficial for a smaller company willing to take on some risk. An example might be a new product idea brought to a smaller engineering company that is radically different or not fully funded. By going into a joint venture and partially funding the project (assuming they believe in it), they could see large payoff. The lesson here is to investigate opportunities, but be willing to take risks that larger companies will not.
   • In the show, this often meant working with unsavory or misunderstood people in society.
2. Agility in all aspects. Smaller companies are more likely to be able to adapt to situations.
   • This could mean picking up a new piece of software quicker, responding to a customer's changing needs quicker, not being bogged down with corporate bureaucracy, being able to fly under the radar of larger competitors, really anything that means you have the advantage as the little guy.  The lesson here is to maintain that agility (even if you begin to grow as an organization) in order to succeed.
   • In the show, they had lots of tricks up their sleeves to maneuver around the Alliance, often outrunning them or tricking them when in a tough spot.
3. Your jobs will be almost entirely referrals.
   • Almost all work is found through connections, either by word of mouth recommendations or prior experience with a customer. It's important to remember that your reputation as an engineer can lead to future success, so to maintain that like you would any other skill. New work will also be an active social task, either asking current connections who needs help or asking for recommendations. And yes, social media can count as a social activity to find new work, though I would not count on it as the only method of finding work today.
   • In the show, the reputation of the crew got them jobs and respect while continually mobile and moving from planet to planet. They also had to take a few not-so-fun jobs.
4. Trust the people on your team. And make sure you like them.
   • If you're working in a small team, the likelihood that you spend more time with them than your family is pretty high. It's a reality that smaller businesses don't have structured hours. That's because much like the Firefly crew, finding work and getting the job done is all you can do to survive. It's not until you are successful that you can be choosy about which jobs to take and which you don't. And in the mean time, the job at hand will be very time consuming; so choose your team wisely.
   • In the show the crew was basically like a family and their isolation from others while in space was pretty drastic.
5. The focus is on completing the job, not necessarily perfection on all fronts.
   • This is exemplified by the scrappy nature of Malcolm Reynolds and his crew and is a necessity for small engineering businesses. When resources and money are tight, the main design constraint is getting the job done. This often means going with proven solutions--so you might start with a reference design or development board instead of trying to start from scratch. This means favoring simplicity and elegance in design solutions over complexity, regardless of how "cool" the complex solution might be. The emphasis on completion can help you plot the fastest course to get to the end of the design, and then focus your energy on removing the obstacles that are guaranteed to pop up (boards are late, can't get parts, etc).
   • In the show they did what they had to and often improvised in order to get the job done. Also since it was a show luck seemed to favor them a few times...

So there you have it: how I view the future of engineering, especially for those not choosing to work for corporations. Both have their benefits and drawbacks, but I believe the choice between the two will continue to be much more polarized. Those choosing the later and striking out on their own may have hardships along the way, but will be rewarded with the freedom to do what they choose and when they want to do it (with the ultimate restriction being putting food on the table).

I'm sure I could compare engineering to a lot of things, but this one seemed to fit. Did I miss any aspects of being a small engineering business? What do you think?

Over on The Amp Hour, I've been known to call ham radio operators, "The Rock Stars of Analog". This is meant for the ones that are out there making their circuits using the dead bug method or otherwise. Jason Milldrum from NT7s.com has confirmed this belief with a picture in his latest posting about his RF kit making business:

I mean would you LOOK at that thing??? It's awesome! Plus it transmits radio signals, so it's just that much more magical. I know the theory behind RF, but I still geek out whenever I think about radio stuff. Anyway, thanks to Jason for posting the picture on his site and on Flickr. Check out his blog for more info as it comes available!

Boy is it hot in here or is it just me? Why's that gizmo over there giving off so much heat?

Power budgets are a necessity these days. Due to increasing regulation, we're seeing devices that must comply with efficiency limits in their power conversion (using a switching power supply or otherwise).

So what is a power budget? Much like a budget you might have for your personal finances, a power budget shows where all the possible power will be used by a device to by breaking it down into components and categories. In some situations, you might be told up front that you will have 3W available to run your design. However, sometimes as designers we start by calculating the total power a system needs and then taking actions such as replacing parts or redesigning circuits to cut back power to an acceptable level. So why might someone want to do a power budget from day one?

1. Power availability -- While you might have more power today, it doesn't mean you'll have it tomorrow. Designing a system for 3 W power consumption may be acceptable now, but designing a lower power system may meet future regulations. And the trends in the industry point in that direction.
2. Battery Life -- If your device is running off a battery, you likely do not have a choice whether you are doing a power budget. You want to maximize the life of your device on a single charge (assuming it is using rechargeable batteries) and your customers want the same. Just a few weeks ago I was complaining publicly on The Amp Hour about my new device with poor battery performance. Doing a power budget will point to the components consuming the most power so you can later optimize for longer battery life (hopefully this was a design constraint from the beginning).
3. Heat generation -- Heat is an unfortunate side effect of working with electronics. However,  it also has a 3 direct effects on your product and how it is used.
   1. User discomfort -- No one likes having a hot laptop sitting in their lap. Nor a cell phone that is uncomfortable to hold.
   2. Circuit robustness -- An often quoted specification of an op amp is the voltage offset drift. This sensitivity to temperature can have dire effects in systems that rely on analog accuracy. However temperature changes can create conditions that are unfavorable and could even cause device failure (such as thermal runaway). The heat of the whole system can end up affecting individual components as the nominal temperature inside your device rises.
   3. Product lifetime -- The lifetime of a product can be drastically reduced by higher than normal temperatures inside the device. Extreme temperatures can begin to dry out capacitors and cause others to fail catastrophically. While it is possible for systems to fail in a drastic manner, the more likely outcome is a product that does not last for its specified lifetime. An example might be a TV that has a less vibrant LCD after 5 years due to excessive heat and component drift and fatigue. If the product was designed to have lower heat, the product would have lasted longer. For more on how to design and prevent early failures, check out Dave's video blog about heatsink design.
4. Cost (sizing) -- More power means you need larger components. Other than the obvious requirement of needing more space (duh), it often correlates to higher cost components. Not only will you need larger packages for your components such as op amps and comparators in order to better dissipate heat. You'll also need a larger power supply with more reliability. If a 5W and 20W power supply with 12V output are compared, the 5W supply has smaller magnetics and less wiring because there is less total current that needs to pass through.

So let's look at an example power budget (click for a larger version):

As you can see, not much more is required than your datasheets and a spreadsheet type program. Even simpler is a piece of paper but I prefer the built in math functions of the spreadsheet program. The first two columns (A&B) are simply identifiers to allow you to recognize which components correspond to which set of data. The next two columns (C&D) determine the multiplicative factor. If you have 5 components that contain 4 op amps per, then that will consume 20x the power of a device that has the same supply current needs but only one op amp per and there is only one on the board.  The next two columns (E&F) show how much current each individual component contributes and then the sum of all the components of that type contribute. Note that this parameter on a data sheet would be listed as "supply current" or "active current". The "quiescient" number is when the device is in a resting state and will likely be much less than the active number (and not relevant for this example). Finally, the supply voltage is listed (in column G) to calculate power (using the formula P=I*V) which is listed in column I per device. All of these contributors are summed, an efficiency is estimated (I assumed a poor efficiency linear type supply) and the total power required input to the device is given. Further calculations could result from much of this initial data.

I would be remiss without mentioning something about power budgets: you're still going to guess about certain things. In fact it will be many different things. You might not have perfect data about your components. You might not completely trust the "typical spec" of one of your components. This is the point where you design in a margin of error. However, just like many other aspects of engineering, this is where tradeoffs come into play. You might want to design in 4 times more power capability than you calculate (to feel safe), but there are cost and spec requirements to consider. You will have to determine how confident you are in your design and how many resources you have available to your design. In the above example where the 5V parts require 408mA from the supply (~2W), I might over spec the part by designing in a part that is capable of supplying 600mA. The (50%) margin of error allows for future expansion (might need to solder in an extra part or two) and also gives a cushion if anything was miscalculated. In some situations this 50% might be too much (think a very low-cost, high volume design) or might be too little (think a military, high reliability design). It all depends on the situation and requirements.

Power budgets can be very powerful depending on the amount of time and effort you put into them. Otherwise they are educated guesses which may or may not be helpful to your project; how helpful they are might also depend on where you are in the design cycle. As stated before, these budgets are more and more of a necessity in a world more power conscious and with devices that continue to shrink. Your customers will expect longer battery life and your products to have yet more features. Teach yourself how to do power budgets now and it will pay dividends for you in the future.