There’s a simple equation helping define how much power you get from an electrical system, and it has been invented since ages: U=R*I (the Ohm law). It’s the first thing kids learn in their physics class about electricity. Still, there are situations in green energy production when this equation doesn’t help us much, because the U (voltage) is so low it can’t open up any other electronic energy harvesting device (cheap one, not lab conditions), so we decide not to use that energy source at all, or increase its voltage output by serializing a sum of them. Examples of such energy sources are small photovoltaic cells, thermocouples, electromagnetic sources, etc.
A company called Advanced Linead Devices, from Sunnyvale, CA, has designed a MOSFET (a power transistor, you may have one your stereo at home – it basically looks like the picture above) that can open itself to very tiny, small, voltages, and it’s called “zero-threshold MOSFET”. Well, the transistor by itself doesn’t do much, but aided by a circuit they built around it, it can use those small voltages we were talking about earlier.
Bob Chao, CEO of ALD, describes it: “This analog circuit can take advantage of ultra-low power supply voltages in the neighborhood of 100 millivolts [0.1 volts] and boosts it to 4 volts so that it can charge energy-harvesting modules.”
They drive the voltage from the circuit onto a capacitor, and then, when the capacitor is loaded, it is then switched to drive intermittent duty-cycle devices such as remote sensors.
Now, a little explanation for electronic geeks: classic transistors need at least 0.7 volts to kick in, but the ALD engineers biased the MOSFET input with buried, floating gates with a charge of 0.7 volts, and this made the transistors to trace small voltages, because the bias voltage on the floating gate adds to trace inputs, making them appear to be above 0.7 volts.
“The challenge was how to make a circuit work with energy sources that only supply 100 millivolts output” Chao said, and then ” boosting them by 40 times to 4 volts. Now we can harness the trace outputs from sources that were not useful before.”
ALD says that their voltage booster circuit will enable a new generation of power sources. They will be used in medical implants, remote and photo sensor arrays, wireless transmitters, RFID tags, and other embedded apps. Their circuit is now a prototype, but they promise it will be available to customers by the third quarter of 2009.
It’s interesting how analog circuitry can still make a difference in today’s all-digital world. But let’s not forget… digital is analog at its core. We still have to keep our eyes wide open and still evolve in the rusty, old, classic, good times pure analog circuits science once in a while.