Bendable Light: The Emitter, Not the Rays

As analog design engineers, part of what we design is power supply circuitry.

One of the most common power supply circuits we are designing lately is the constant current supply for powering a series string of LEDs. The topology is almost always a switchmode regulator. If the power source is the AC line and galvanic isolation is not required, a buck regulator is used. Here's an example (that has constant current output) from an Intersil data sheet for the ISL1903:

A conventional off-line switcher using a buck topology

A conventional off-line switcher using a buck topology

Or, if you need galvanic isolation, the flyback topology is the likely choice. Again, from the ISL1903 data sheet (and again, with constant current output):

A conventional off-line switcher using a flyback topology

A conventional off-line switcher using a flyback topology

Lighting fixtures or luminaires based on these and similar LED circuits represent an improvement over the compact fluorescent lamp (CFL). They run cooler, don't have even a trace amount of mercury (and mercury in lamps makes some folks mad as hatters), and produce better color rendering compared to the rather “notchy” spectral output from a CFL.

So, have we reached the ultimate device to transform electrical energy into light? Probably not. Especially since scientists at Wake Forest's Center for Nanotechnology and Molecular Materials are working on a different solid state version of the LED.

Properly speaking, this is not an LED as semiconductor diodes are not involved. Instead, a sheet of plastic makes the light. Specifically, the light is based on a field-induced polymer electroluminescent (FIPEL) technology. The director of this research, David Carroll, a physics professor, points out that a FIPEL-based luminaire can produce even better color rendering without the flicker, buzz, or mercury the many people find so annoying with fluorescent lamps (both compact and uncompact). Also, there is no glass envelop so no breakage hazard.

Even compared to LEDs, performance is better. Conventional “white” LEDs tend to be bluish or gray-white. Of course, you can get any color you want with LEDs by using three primary color arrays and adjusting forward current through each. But that uses more LEDs than the gray-white version, takes up more circuit board space, and probably triples the cost of the drive circuitry.

As to how it works, the short version is that the electrical charge is converted to light in the polymer. The device is sort of a light emitting capacitor. The longer answer can be found in an online study published by the Journal Organic Electronics. Organic chemistry is beyond my ken, so I won't attempt an explanation here. Besides, I'm more interested in getting a sample and lighting it up.

It appears to work with a low AC voltage applied (not a constant current device like an LED). The researchers were exciting it at 80 kHz, so drive circuitry should not be exotic by any means. The form factor can be flat panels of various sizes or can be shaped to resemble the conventional Edison-base light bulb. Power efficiency (for now at least) is comparable to a CFL.

Looks like I may have to wait up to a year before I get my sample.

5 comments on “Bendable Light: The Emitter, Not the Rays

  1. David Maciel Silva
    January 29, 2013

    Hello everyone

    Probably not the same model that is discussed in the article, but analyzing the characteristics found nearby.

    A good choice for the power supply is this small integrated circuit LNK306P, although this iten can be directly connected to an AC power source.

  2. Brad Albing
    January 29, 2013

    I was thinking about the power supply requirements. An IC that can be powered straight from the mains like those Power Integrations devices are good for an applications such as this (as low as you don't need galvanic isolation). Once you have the low-voltage DC, then you just need a low power oscillator running at around 80 kHz to drive the panel electrodes. I definitely want to try this on the bench.

  3. David Maciel Silva
    January 29, 2013

    Perhaps ci indicated that might help somehow.

    The only thing I see is the frequency of operation 66khz.

  4. WKetel
    January 31, 2013

    There have been electroluminescent devices around since the mid-1960's, so the concept is not new, although from the limited details provided the particular mechanism may be new here. Of course there is always room in the applications area for new types of light sources, and having a non-diode light source will probably make the power source design a bit easier. Of course the requirement for AC will mean a different set of design requirements, but that should not be a problem either.

    The big challenge, as always, will be in the jump from a laboratory sample to a commercially available product. That will take a bit of effort, no doubt.

  5. Brad Albing
    March 28, 2013

    An addendum – there should be parts available from IR, Supertex, and Power Integrations that would make it easy to do the line voltage-to-lower DC voltage cheap and easy. After that, the power oscillator + drive cktry is easy.

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