“Power Conversion” is a conversion from one form of energy to another. It doesn't preclude the conversion of input energy into light, instead of more conventional load profiles that power supply engineers are generally accustomed to. In fact, I found out the hard way how difficult this area of power conversion can really be. Far more difficult than your average DC-DC converter!
My first exposure to electronic ballasts was, it now seems, light years ago (no pun intended), while I was working in the swank and well-equipped central R&D labs in Bombay of one of India's largest electrical manufacturers. That company is to India, probably what Siemens is to Germany – with a huge and diversified market share in almost everything 'electrical'.
India, of all the hot, confusing, bustling places on earth, may actually form the best place to see what the brouhaha about ballasts is all about. It is the perfect testing ground (and potential graveyard) for all electronic ballasts, big and smallthe ultimate leveler if ever there was one.
We are aware that electronic ballasts are universally known to provide more stress-free working environments, attributed to their steady flicker-free light, besides other nice features like instant-start, the more recent auto-dimming capability, and power-factor correction. Though electronic ballasts have been available for a dozen years, it is very surprising that sales have barely started to exceed copper-wound (or 'magnetic') ballasts, which are known to be physically bulkier, heavier, and much less energy efficient. (Touch one and you will surely scream 'yeeeooowwaaaaaasste').
True, electronic ballasts cost more, but you are supposed to get paid back handsomely in a few years in reduced energy costs. Some governments also continue to contemplate subsidies to help consumers afford such ballasts. But I don't think it has happened yet.
In a typical office environment, the light bills can amount to 40% of the total energy costs. There is great need to conserve energy in lighting, much as we are doing with standby power requirements of appliances. Community-conscious and inherently progressive organizations, like my employer for example, have installed PIR (passive infra-red, i.e. body-heat) sensors almost everywhere to turn the lights on and off as needed. I suspect they also use electronic ballasts. Remember, PIR sensors do help at night, but clearly can't save energy on their own during the day. For that electronic ballasts must be used in conjunction.
(As an aside, we may not conserve THAT much energy if engineers like me continue to leave their computers and monitors on the whole day, night, through weekends and on long breaks, spicing up their screensavers with graphic-intensive witticisms like “go away”, “scat”, or simply “attending a meeting” refreshing over and over again. I had heard of endless meetings, but a 10-day blinking message can takes really take the cake.)
California, with its high energy costs is certainly waking up to the potential savings from electronic ballasts this year. See a very useful discussion of ballast sales and impending regulations starting 2005 with the papers at www.aboutlightingcontrols.org.
Another very nice piece on the myths associated with ballasts and tubes can be found at www.energyusernews.com.
Note that the fluorescent tube also responds rather positively, in terms of its own life and performance, when driven at over 20 kHz (as in an electronic ballast), rather than with 60Hz (as in magnetic ballasts). Tube-replacement costs are thus significantly reduced with electronic ballasts. But, wait! What about the life of the ballast itself? That is another story altogether!
Electronic ballasts unfortunately have been plagued by failures. (See lightingdesignlab.com.)
So how do we as traditional power supply engineers provoke incipient failures in power supplies? We increase the stress levels, especially during design phases. Simple burn-ins are actually too kind to the system! To demonstrate an exaggerated burn-in situation, let's take an 'Amazing Race' detour, and parachute down directly into a remote residential area somewhere in the heartland of India.
Oh I know you feel suddenly out-of place! Here time stands still. Well, almost! After a moments rest, you can probably observe that the AC utility lines and the frayed household wiring haven't been replaced for several decades now. But worse! Here we happen to be ensconced by several industrial units using heavy electrical machinery, even during the night.
The mains input in India is officially supposed to be 230VAC or is it 220V or 240V? Even I will never know. In fact, that may be a rather redundant question, especially here, because the voltage is known to drop down to a steady level of almost 120VAC (no typo here: one hundred and twenty!). More so in the summer months (9 of them in India) when all the fans and air-circulators try to come on at the same time. The standard household incandescent bulb is now seen glowing faintly in the distance, too dim to even see where the TV and Fridge lie gasping for breath.
So it may confer minor bragging rights with inquisitive neighbors, to possess fluorescent tubes in every room of the house! The sage had mentioned these tubes provide more acceptable illumination level even at such low input voltages. Provided they work!! To get them to work, magnetic ballasts are literally powerless. An electronic ballast can work in principle, since it is basically the flyback (buck-boost) topology principle. Aha! Out with the sage!… I now see a power conversion engineer firmly entrenched here too! And this poor guy has to ensure his circuit design can get the tube to fire, and continue to run – at such a low input voltage.
However, we can't be in the business of designing and selling one ballast design for one area and another circuit design for another area or locality. So now let's take the same ballast and move inside an industrial facility (with better local wiring). We are not surprised to find this is where the maximum usage of fluorescent lighting occurs. Rows upon rows of multi-tube ceiling fixtures, as in all countries. Sounds familiar and encouraging. I too feel almost at home now.
But now we sadly note that the utilities often raise the voltage at the substation end, just to compensate for some arbitrary calculated ohmic drops across miles and miles of lines. But suppose we happen to be the unlucky business unit sitting 'up close and personal' to the actual distributing substation. The intervening ohmic drops are thus virtually negligible. What we get coming into our facility 24/7/365 is a steady overvoltage of over 270VAC!
But now if we dare to use heavy industrial machinery on our premises, we also know that that can unleash huge inductive spikes back into the mains coinciding with the solenoids and motors turning off. As any typical ballast manufacturer in much of the third-world (and Eastern European, especially the former Soviet bloc), we are faced with the daunting design task of ensuring rock-solid reliability under steady voltage variations of about 100-300VAC, overlaid with huge spikes.
In fact the relevant qualifying test is usually based on keeping the ballast in operation, and simultaneously applying at the input, the well-known 8/20 μs lightning surge test . No short-term or long-term damage should ever occur. Note that these line surges are of frequent occurrence in these areas (rather than a rare 'one in a blue-moon' type of thing), so we just cannot rely on MOV's (Metal Oxide Varistors) which have inherent lifetime/wearout issues.
Nor can we rely on TVS's (silicon Transient Voltage Suppressors) because the latter often can't even handle the type of energy a single 8/20 μs spike throws at them, least of all a succession of spikes at a certain constant rate per minute.
But that's not all! Any ballast in the world must be able to survive the 'deactivated tube' test. That is where the gas has leaked out, but the heating filaments are still present, and so the circuit keeps trying to start the tube endlessly (at the elevated voltage and frequency needed to cause it to strike). In fact, this particular test killed every ballast we ever tested in Bombay with no exception (except the one I finally designed! You knew I would say that, but it's true!). We burned out every known name-brand ballast we actually imported at that time from USA, Europe, Singapore, Korea, Japan (you-name-it) into India. We personally performed the last rites. And it was a virtual crematorium.
So India is possibly a great place to hone the design skills for any mains input ('off-line') power conversion device. Remember that when you set up a design center in Bangalore! This should help take the Sting out of it.
Next month will get into the nitty-gritty technicalities, and tell you exactly how the simple electronic ballast actually works, and how we ended up enhancing the reliability besides reducing the manufacturing cost by a factor of almost 2 in the course of what was probably the most successful R&D technology transfer project in that company. Not that they remember me anymore!
Don't forget to write me at firstname.lastname@example.org or email@example.com and do copy Steve at firstname.lastname@example.org, if you don't want your energy to be wasted! And all power to you!
Switching Power Supply Design & Optimization is published by McGraw-Hill. User reviews at Amazon.com identify it as the new “bible” on switching power supply design.”