LTC3108IDE datasheet(12/20 Pages) LINER

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LTC3108

3108p

The low voltage capability of the LTC3108 design allows

it to operate from a TEG with temperature differentials

as low as 1°C, making it ideal for harvesting energy in

applications in which a temperature difference exists

between two surfaces or between a surface and the am-

bient temperature. The internal resistance (ESR) of most

cells is in the range of 1Ω to 5Ω, allowing for reasonable

power transfer. The curves in Figure 2 show the open-

circuit output voltage and maximum power transfer for a

typical Peltier cell (with an ESR of 2Ω) over a 20°C range

of temperature differential.

TEG Load Matching

The LTC3108 was designed to present a minimum input

resistance (load) in the range of 2Ω to 10Ω, depending

on input voltage and transformer turns ratio (as shown

in the Typical Performance Characteristics curves). For

a given turns ratio, as the input voltage drops, the input

resistance increases. This feature allows the LTC3108 to

optimize power transfer from sources with a few ohms

of source resistance, such as a typical TEG. Note that a

lower source resistance will always provide more output

current capability by providing a higher input voltage

under load.

Peltier Cell (TEG) Suppliers

Peltier cells are available in a wide range of sizes and power

capabilities, from less than 10mm square to over 50mm

square. They are typically 2mm to 5mm in height. A list

of Peltier cell manufacturers is given in Table 3.

Table 3. Peltier Cell Manufacturers

Fujitaka

www.fujitaka.com/pub/peltier/english/thermoelectric_power.html

FerroTec

www.ferrotec.com/products/thermal/modules

Melcor

www.melcor.com/tec.html

Micropelt

www.micropelt.com

Nextreme

www.nextreme.com

TE Technology

www.tetech.com/Peltier-Thermoelectric-Cooler-Modules.html

Tellurex

www.tellurex.com

Thermopile Generator

Thermopile generators (also called powerpile generators)

are made up of a number of series-connected thermo-

couples enclosed in a metal tube. They are commonly

used in gas burner applications to generate a DC output

of hundreds of millivolts when exposed to the high tem-

perature of a ﬂame. Typical examples are the Honeywell

CQ200 and Q313. These devices have an internal series

resistance of less than 3Ω, and can generate as much as

750mV open-circuit at their highest rated temperature. For

applications in which the temperature rise is too high for

a solid-state thermoelectric device, a thermopile can be

used as an energy source to power the LTC3108. Because

of the higher output voltages possible with a thermopile

generator, a much lower transformer turns ratio can be

used (typically 1:20, depending on the application).

Photovoltaic Cell

The LTC3108 converter can also operate from a single

photovoltaic (solar) cell operating in indoor lighting, where

the available power is orders of magnitude less than in

direct sunlight. This capability allows the LTC3108 to power

circuits at light levels far too low for even very low input

voltage boost converters.

Non-Boost Applications

The LTC3108 can also be used as an energy harvester

and power manager for input sources that do not require

boosting. In these applications the step-up transformer

can be eliminated.

Any source whose peak voltage exceeds 2.5V AC or 5V

DC can be connected to the C1 input through a current-

limiting resistor where it will be rectiﬁed/peak detected. In

these applications the C2 and SW pins are not used and

can be grounded or left open.

Examples of such input sources would be piezoelectric

transducers, vibration energy harvesters, low current

generators, a stack of low current solar cells or a 60Hz

AC input.

A series resistance of at least 100Ω/V should be used

to limit the maximum current into the VAUX shunt

regulator.

APPLICATIONS INFORMATION

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