Design Article
Low power solar energy harvesting in a compact footprint
Jeff Gruetter, Linear Technology Corp.
5/10/2011 4:50 AM EDT
LTC3105
The LTC3105 incorporates a feature that maximizes efficiency at light load while providing increased power capability at heavy load, adjusting the peak and valley of the inductor current as a function of load. Lowering the peak inductor current to 100mA at light load optimizes efficiency by reducing conduction losses. As the load increases, the peak inductor current is automatically increased to a maximum of 400mA. At intermediate loads, the peak inductor current can vary between 100mA to 400mA. This function is overridden by the MPPC function and will only be observed when the power source can deliver more power than the load requires.
Input undervoltage lockout
In applications such as photovoltaic conversion, the input power source may be absent for long periods of time. To prevent discharge of the outputs in such cases, the LTC3105 incorporates an undervoltage lockout (UVLO) that forces the converter into shutdown mode if the input voltage falls below 90mV (typical). In shutdown, the switch connecting AUX and VOUT is enabled and the LDO is placed into reverse-blocking mode and the current into VOUT is reduced to 4uA typical. Reverse current through the LDO is limited to 1uA in shutdown to minimize discharging of the output.
Conclusion
The LTC3105 energy harvesting DC/DC converter is specifically designed to dramatically simplify the task of harvesting and managing energy from low voltage, high impedance alternative power sources such as photovoltaic cells, TEGs (thermoelectric generators) and fuel cells. Its unique design enables it to start up from input voltages as low as 0.25V, and provides very high efficiency over a wide range of input voltages and current levels. Onboard maximum power point control optimizes the energy extracted from a wide range of sources under a wide range of conditions. Its very simple and compact solution footprint makes it a straight forward power solution for a growing number of energy harvesting applications.
About the author:
Jeff Gruetter is Sr. Product Marketing Engineer, Power Products, at Linear Technology Corp. (Milpitas, Calif.)
The LTC3105 incorporates a feature that maximizes efficiency at light load while providing increased power capability at heavy load, adjusting the peak and valley of the inductor current as a function of load. Lowering the peak inductor current to 100mA at light load optimizes efficiency by reducing conduction losses. As the load increases, the peak inductor current is automatically increased to a maximum of 400mA. At intermediate loads, the peak inductor current can vary between 100mA to 400mA. This function is overridden by the MPPC function and will only be observed when the power source can deliver more power than the load requires.
Input undervoltage lockout
In applications such as photovoltaic conversion, the input power source may be absent for long periods of time. To prevent discharge of the outputs in such cases, the LTC3105 incorporates an undervoltage lockout (UVLO) that forces the converter into shutdown mode if the input voltage falls below 90mV (typical). In shutdown, the switch connecting AUX and VOUT is enabled and the LDO is placed into reverse-blocking mode and the current into VOUT is reduced to 4uA typical. Reverse current through the LDO is limited to 1uA in shutdown to minimize discharging of the output.
Conclusion
The LTC3105 energy harvesting DC/DC converter is specifically designed to dramatically simplify the task of harvesting and managing energy from low voltage, high impedance alternative power sources such as photovoltaic cells, TEGs (thermoelectric generators) and fuel cells. Its unique design enables it to start up from input voltages as low as 0.25V, and provides very high efficiency over a wide range of input voltages and current levels. Onboard maximum power point control optimizes the energy extracted from a wide range of sources under a wide range of conditions. Its very simple and compact solution footprint makes it a straight forward power solution for a growing number of energy harvesting applications.
About the author:
Jeff Gruetter is Sr. Product Marketing Engineer, Power Products, at Linear Technology Corp. (Milpitas, Calif.)
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Frozen_One
5/25/2011 2:43 PM EDT
Please consider offering larger images to click on for better clarity.
Thanks for a great article!
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