The energy harvesting arena has become more interesting with the advent of an energy management chip designed to work with a harvesting device alone, without the use of a companion battery.
The ALD EH4200 Series from Advanced Linear Devices are designed to step-up or boost the output voltage of widely used energy generators such as thermoelectric generators, electromagnetic coils, single photovoltaic cells, and infrared emitters. The output voltages of such devices are generally in the tens-of-millivolts range. Power outputs range from micro to milliwatts.
The lower threshold for the ALD chip extends down to less than 0.1V and 100 uA. The interesting aspect of their technology is that when there is no energy present to be harvested, the ALD circuitry consumes no power and does not need a wake up time. As soon as power is available to be harvested, it can be captured and transformed into useful electrical energy.
Key to the operation of the new energy managers are micropower floating-gate MOSFETs and a special self-starting transformer-oscillator stage. When operating directly from one of the aforementioned energy generators, the modules create a voltage gain ranging from 75 to 150.
There are two micropower step-up booster models available, the ALD EH4205/4295, each with different source input impedance matching qualities. The ALD EH4205 features a nominal input impedance of 50 Ω while the ALD EH4295 features an input impedance of 950 Ω. The company says future models will be added with source input impedances designed for other energy generators.
The EH4205/4295 output can directly connect to the input terminals of an energy harvesting module using a standard two-wire cable. ALD booster modules can also be used, independently for trickle-charging batteries or super-caps, including situations where the energy generating input source is intermittent and not well controlled or regulated.
Both EH4205 and EH4295 are available for immediate delivery and can be ordered from DigiKey or Mouser Electronics. Small quantities are priced from $41.00 each. Evaluation kits and cable assemblies are also available to simplify bread boarding and test.
More info: Advanced Linear Devices, http://www.aldinc.com/pdf/EH4205.pdf