Low Input Voltage and Maximum Power Point Control Simplifies Energy Harvesting

Summary

In this presentation, Fran Hofford, an application engineer at Linear Technology, discusses the LTC 3105, a DC-to-DC converter designed for efficient energy harvesting, particularly from solar energy. The LTC 3105 uses Maximum PowerPoint Control (MPPC) to extract optimal power from solar cells, adapting to changing sunlight conditions. It powers lithium-ion batteries, preventing overcharging and deep discharge through its integrated LTC 470 charger. The technology ensures reliable energy harvesting and battery protection, making it ideal for low-power solar applications. This solution maximizes energy efficiency, even under varying light intensities, while maintaining battery health and longevity.

Takeaways

• 😀 Energy harvesting extracts energy from ambient sources and converts it into usable power.
• 😀 Solar energy is an abundant, unlimited power source, generating approximately 1000 watts per square meter in full sunlight.
• 😀 Solar cells produce direct voltage from sunlight but require additional circuitry to maximize power output and manage energy storage.
• 😀 Solar panels are made of individual cells connected in series or parallel to increase power output.
• 😀 The output power of solar cells is maximized at a specific voltage and current range, typically between 700 and 800 mV.
• 😀 The LTC 3105 is a DC-DC step-up converter designed for energy harvesting, using Maximum PowerPoint Control to optimize power extraction from solar cells.
• 😀 The LTC 3105 supports low voltage solar applications, including charging lithium-ion batteries with a 250 mV startup voltage.
• 😀 The converter's MPPC prevents solar panel voltage from dropping too low when sunlight intensity fluctuates, maintaining stable output power.
• 😀 The LTC 470 shunt battery charger ensures the lithium-ion battery is not overcharged by limiting the float voltage.
• 😀 Battery temperature sensing in the LTC 470 charger helps adjust the float voltage to protect the battery from overheating.
• 😀 The LTC 3105 and LTC 470 combined offer an efficient solution for low-power solar applications, maximizing energy output and battery longevity.

Q & A

What is the primary function of the LTC 3105?

The LTC 3105 is a step-up DC to DC converter designed for harvesting electrical energy from ambient sources, like low-voltage solar cells and thermoelectric generators. It maximizes power extraction through Maximum Power Point Control (MPPC).

Why is energy harvesting important and how is it typically implemented?

Energy harvesting extracts energy from ambient sources like solar power, converting it into usable electrical energy. Since these energy sources are not available 100% of the time, energy storage, usually in rechargeable batteries, is required.

What are some of the key features of the LTC 3105?

The LTC 3105 features synchronous 400mA switches, low 250mV startup voltage, a 6mA low dropout regulator, burst mode operation, and the ability to operate with input and output voltages that can differ. It also includes a 10-pin DFN or 12-pin MSOP package.

How does the LTC 3105 manage power extraction from a solar panel?

The LTC 3105 uses Maximum Power Point Control (MPPC) to adjust the output current in response to changes in sunlight intensity, ensuring that the solar panel operates at its optimal voltage for maximum power extraction.

What is the role of the solar panel in the circuit described?

The solar panel powers the LTC 3105, which in turn boosts the voltage to charge a lithium-ion battery. The solar panel's output depends on sunlight intensity, and the LTC 3105 adjusts the power drawn to maintain the maximum power point.

What happens to the solar panel's output voltage when sunlight intensity decreases?

As sunlight intensity drops, the output voltage and current of the solar panel decrease. However, the LTC 3105's MPPC feature prevents the panel's voltage from dropping too much, maintaining power delivery to the circuit.

Why is it important to maintain the solar panel's output voltage in a specific range?

Maintaining the solar panel's output voltage between 700 and 800mV ensures that maximum power is extracted. If the voltage drops outside this range, the efficiency of the power extraction decreases.

What happens if the Maximum Power Point Control (MPPC) is disabled?

When MPPC is disabled, the solar panel's output voltage can drop significantly, potentially below the converter's minimum input voltage, causing a reduction in output current and less efficient power conversion.

How does the LTC 470 shunt battery charger function in the circuit?

The LTC 470 controls the lithium-ion battery's float voltage and indicates when it is fully charged. It ensures the battery is not overcharged and helps regulate the battery's charging process to avoid damage.

What additional features does the LTC 470 provide for battery management?

The LTC 470 includes battery temperature sensing using an NTC thermistor to adjust the float voltage at higher temperatures, an active output to signal when the battery is nearly charged, and a low battery output to prevent overdischarging.