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."

Comments

Current products DONT use transformers

[Chmarr]

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?

Re:Current products DONT use transformers

[FreeMars]

That's going to be a big surprise to the folks who manufacture transformers for switching mode power supplies.

Yes, they are smaller than the transformers needed for non-switching power supplies, but they are there.

Re:Current products DONT use transformers

[Animats]

Some wall transformers use switching power supplies, with a small high-frequency transformer after the chopper, and some are linear, with a front-end transformer running at 50/60Hz.

Worth mentioning is the forged UL safety label problem. If a power supply doesn't have a UL or CSA label, don't buy it. It will probably catch fire if shorted or even heavily loaded. A UL label must have the UL logo and a certification number. UL certifications can be looked up here. This is worth doing for desktop computer power supplies, for which forged certifications are a big problem. The ones that catch fire are almost invariably uncertified. UL requires that no single component failure can cause a fire.

Re:Current products DONT use transformers

[albeit unknown]

Totally wrong.

Most electronic products, especially those using switch-mode DC power supplies, do use transformers. The reason is that the transformer provides galvanic isolation from the AC mains. This helps prevent transients like lightning strikes from propagating through the device. Also, it prevents the wrong parts from becoming "hot" because the cord is plugged in backwards.

Products that do not have transformers have much more stringent requirements for creepage and clearance distances, and are usually simple devices. A drill, for example. Hard to do with an electronic device with lots of buttons and slots.

The high-frequency operation of a switch-mode power supply does allow the magnetics (transformers and inductors) to be much smaller than their 60 Hz linear counterparts, but they are still there.

Please refrain from commenting about something you know nothing about, as someone may read your post and build something lacking the necessary safety features and hurt themselves.

Piezoelectric Transformers

[Gary Whittles]

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.

Re:DC Power Distribution.

[TeknoHog]

Regulators are very much not the equivalent of transformers. They can only give a voltage drop, but the current is kept constant, which is why some energy is wasted.

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.