March 2013

DocID023264 Rev 2

1/17

AN4123

Application note

STEVAL-ISV015V1 up to 2.5 W solar USB charger

By Domenico Ragonese

Introduction

The STEVAL-ISV015V1 is a demonstration board mounting the SPV1040 device (solar

energy harvester) as input stage and the LD39050PUR device (low noise and low quiescent

current voltage regulator) as output stage. It targets any portable application powered by

USB supply and merges the capability of the SPV1040 device to maximize the power

extraction from solar modules with the high precision voltage regulation of the LD39050

device. It is shown in

Figure 1.

Figure 1. STEVAL-ISV015V1 demonstration board

The board has been designed to harvest power from PV panels and to supply loads

requiring up to 2.5 W (5 V, 500 mA) through a mini-USB (B type) connector. Between the

two stages, a 440 mF super capacitor stores the harvested energy even when load is not

connected or, if connected, it needs less power than that available from the source.

The application components at the input stage have been selected to optimize the energy

harvesting from polycrystalline PV panels composed of 2, 3 and 4 PV cells in series and

able to supply up to 900 mA. The trimmer VR3 is connected between the PV panel and the

MPP-SET pin of the SPV1040 device and allows the maximum power extraction from the

selected PV panel to be fine tuned. Setting the VR3 = 1 k

Ω is recommended to cover most

application cases. So, other PV panels can also be used but it may be necessary to replace

some of the application components in order to make the system work in the most efficient

way. The PV panel and main application components can be replaced, but the following

guidelines must be carefully considered:

• The PV panel can be selected as long as V

OC

< 5.5 V and I

SC

< 1.65 A

• The inductor L1 can be replaced by considering that it affects the maximum peak current

and that an input overcurrent limit (1.65 A) does not have to be triggered

• The maximum output current can be limited by inserting the current sensing resistor RS1

(0

Ω by default)

For further details on component selection, please refer to Section 6 “External component

selection” of the AN3319 application note. For details on the SPV1040 device and the

LD39050 device features, please refer to the related datasheets.

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