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Piezoelectric Transformers
behoward writes "Tired of those big honking power adapters needed for all your portable toys? Me too! So far the best solution I've seen is the AC adapter for my G4 Powerbook, a sleek combo yoyo/flying saucer; but while it looks good on the desktop, it still makes too big of a bulge in my case when I travel. Now engineers at Penn State are working on a real solution. Hope Apple gets this technology in place in time for the G5 Powerbook."
The current power adaptors don't use transformers. They're switch-mode power supplies, which use a small inductor and a bunch of circuitry to control switching and regulating.
So, yes, the article states that the new piezoelectric transformer will be smaller than regular transformers, but the current laptop power supplies DONT use regular transformers!
So, the real question is, will the piezoelectric transformer be SMALLER than a switch-mode supply, AND, will it be more efficient?
They typically have small flyback transformers. Making them smaller wouldn't allow us to redesign adaptors (or fit them into a pen).
The whole idea of a switching power supply is that it gives a regulated output. A transformer would still give you an AC output, which is useless by itself.
I am doing some graduate studies in this field, so here's a quick breakdown.
Power electronic circuits have traditionally been based on magnetic technology, and until recently, have not been part of the tide of miniaturization and integration advances from which signal-processing integrated circuits have benefited. In an effort to miniaturize power components, acoustic rather than inductive coupling can be used as the basis for a transformer. Note that acoustic coupling can be achieved through piezoelectric *or* magnetostrictive means.
In a piezoelectric transformer, the direct and converse piezoelectric effects are used to acoustically transform power from one voltage and current level to another through a vibrating structure. The converse piezoelectric effect, in which an applied electric field produces a resulting strain in a body, is used to convert an oscillating electric field applied to the left half of a structure, such as a bar, into a vibrational mode of the entire bar. If driven at resonance, standing-wave distributions of large amplitudes of stress and strain result. The resonantly amplified strain in the right half of each bar is converted to a voltage across the output terminals by the direct piezoelectric effect. Depending upon geometry and materials parameters, you can obtain voltage amplifications of various magnitudes, with associated step-downs in current level.
The unique nature of the piezoelectric transformer offers the opportunity for innovative circuit design such as operating above resonance for inductive behavior to achieve soft-switching without compensating inductors.
The YoYo shaped adapters for Apple's PowerBooks have already been replaced by small lightweight adapters. The current ones are tiny and I carry it everywhere without noticing it at all. It looks like the iPod power adapter only slightly larger. Take the current Apple power adapter and compare it to some other laptop manufacturer's power supply and the difference is clear.
Regular switching power supplies also operate in the ultrasonic range.
Well designed supplies are reasonably quiet (as one can verify by making them operate in lower frequencies), so pets tolerate them.
Likewise, badly designed supplies really pollute the airwaves. It's usually impossible to tune an AM radio within 20 meters of a cheap desktop computer PSU.
I have a 12" Powerbook G4(original model), and let me tell you, the AC adapter is just excellent. It is very solidly built, and unlike some of my Apple AC adapters of the past, the wire has not frayed at all. I wrap and unrwap it every day, too, so this is even more impressive.
The small prongs that flip out from the brick are very handy for winding the wire around, and the design is simple, small, and much more durable than other companies' adapters I've used/seen.
But for this fellow to say the yo-yo design was "great" is just silly. The design was good for its time, but I have one, and the wire frayed eventually, and compared to the current white-brick adapter I own, it is a piece of crap.
The dual voltage bit comes from the rectifier being a bridge rectifier when you set the switch to "240" and a voltage doubler when you set the switch to "110", both giving a DC voltage to the switch somewhere around 300V.
That's one way, but most notebook adapters don't have such a switch. Rather, they accept a very wide range of input voltages. They work by simply being able to regulate and handle the full range of voltages; at 90v input the regulator would be passing quite a bit more current through, where at 240v the duty-cycle would be dropped significantly.
The piezo supplies, from what I gathered from the article, are more along the lines of a basic 60-Hz transformer; eg, you get some specific ratio of input/output voltage, without regulation. I'm sure these could be easily regulated, and I'm sure a future version will be.
It's (AFAIK) brand-new tech, so more features will come I'm sure, if the technology takes off.
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For an electrical engineer you don't know a lot do you ? A decent transformer of 48VA (2A, 24V) will run barely warm if its designed right. Increasingly transformer designers are using cheaper and cheaper techniques which has reduced the regulation of small transformers to as much as 75%. A 48VA TOROIDAL transformer runs basically cold, and is smaller than a clenched fist.
A an on-line (90-280 V AC In) SMPSU DOES NOT work in the way you describe. The input stage rectifies the incoming AC to high voltage DC (110 x root(2) )The High direct voltage (500 volts) is then chopped at very high frequency and transformed and isolated by a very small high frequency core.
The piezo electric method is interesting, but TANSTAAFL, and the catch is that piezo materials suffer from hysteresis loss, which results in, you guessed it, heat generation.
Electromagnetic transformers are close to perfect machines, particularly as the size increases.
Steve
Most laptops use about 12 watts?????? If these guys are working towards making their pizo suppkies reach a target of 12 watts of power, then it's going to be a long time before we'll ever be able to use them with real laptops, which can draw 75 watts or more. The article seems high on hype and low on anything meaningful.
I'm an American. I love this country and the freedoms that we used to have.
European standard is 230V, _not_ 220V.
For example, converting from 6 V to 5 V at a current of 1 A means a voltage drop of 1 V. Input power is 6V * 1A = 6 W, whereas output power is 5V * 1A = 5 W. The difference is wasted heat, and you can always calculate this as voltage drop times current. You need to choose a suitable heatsink to accommodate the heat. For many electronic gadgets the current is small enough that the waste is not a concern, but with computers you need several amps, so a regulator would be out of the question.
However, a transformer from 6 V to 5 V would have ideally equal input and output power. Keeping the input at 6 V, 1 A, the output would be 5 V at 1.2 A, i.e. the same power, no waste. However, "DC transformers" are always a little complicated (basically inverter+transformer+rectifier) and there are other losses.
Escher was the first MC and Giger invented the HR department.
From my experience, most switch-mode power supplies use an optocoupler to isolate the feedback loop from the output.
It's simply full of inaccuracies. The piezo transformer is not a new idea. You take a piece of piezo-electric material, excite it in AC (thus making it vibrate) and, with electrodes placed properly on the same piece of material, you get back electric signal from the vibration.
This stuff is already used in low-to-high voltage converters (e.g. the inverter in the laptop panel - its job is to produce high AC voltage for driving the backplane CCFL). However there are tremendous shortcomings when comparing to the mature magnetic energy conversion:
1) LOWER efficiency - if you can get 84% you've got a lucky day. Magnetic-based conversion can easily achieve 90-95%.
2) to work properly, these things must be driven at resonance, i.e. the AC input signal must match the resonating frequency of the piezo-transformer. This is much more difficult (think dynamic frequency tuning) than driving the wide bandwidth magnetic transformer.
3) derived from 2), the driving signal must be sinus (the energy confined in a narrow spectrum). This is very difficult. A magnetic transformer is usually driven in switching-mode - certainly all AC-adaptors (off-line AC/DC converters) for laptops are.
4) the input/output voltage ratio is fixed by the piezotransformer geometry. A ratio higher than 1:10 was very unusual back in 2001 when I designed back-light inverters with them. In contrast, the magnetic transformer is very versatile and, when controlling the insulation between the primary and secondary(ies), you can easily achieve factors of 100s.
5) present piezo materials have much lower power density ratings than the better magnetic cores. This means that for the same 80W AC-adaptor you'll need a much bulkier piezo-transformer than a magnetic transformer to transfer that power.
Did you see any of these major setbacks mentioned in the article? What a piece of crap!
B.t.w. it makes no sense to integrate the AC adaptor in the laptop as it limits its portability. When you're on batteries and you can't use the AC outlet, you don't want to carry with you the extra weight of an useless AC adaptor, do you?
Serban
This is why utilities put limits on power factor, and why some consumer electronics (PC Power supplies) are starting to include power factor correction. Big industrial loads have been doing it for a long time.
We can correct for it, but sometimes the effort is not worth it.