Can SPV1040 Be Used with a Single Solar Cell?

[JOlso.12]

The data sheet and application note for SPV1040 appear to be written on the assumption that the driving solar array has an MPTP output voltage of 2.0V or greater. However, I notice that great pains have been taken during the design of the SPV1040 to make it work at even lower voltages.

**Is it possible to make it run (or at least boot with zero output load) on a single silicon PV cell?**

The answer to this question is probably embedded in the ambiguous meaning of the term "soft start" used in the application note.

Assume that there is a high quality external Schottky diode from input to output to assist the onboard body diode of the PMOS transistor. Assuming a forward voltage of 200mV across the Schottky, this would mean that the output with a single solar cell would never be lower than 600mV-200mV=400mV.

But an output voltage of 400mV is lower than the data sheet specification of 800mV for starting voltage. Does this mean that (even with a huge and intensely illuminated single solar cell) the output voltage could never climb above 800mV because the MOS charge pump won't operate?

Thanks in advance for your input(s) on this.

Jim Olson

Indianapolis, IN US

[paolus]

Hello Jim,

Did you succeed in resolving your issue? I am trying to make this module work with a solar cell but it does not work. The datasheet states that the converter can work with an input voltage as low as 0.3 V. The solar cell I am using is able to provide 0.6 V (Voc) and 100 mA (Isc), but the voltage output is never stepped up using this low input voltage. I have tried even connecting directly a power supply as if it was the solar panel, and the output voltage only steps up with input voltages greater than 0.85 V. Any help coming from your experience would be highly appreciated!

Kind regards.

[JOlso.12]

Paolus,

Absent any feedback from STM tech support I did not pursue this issue further. Thus I have made no further progress on the matter.

It is very difficult to get sophisticated circuits to function at voltages below 0.6VDC. The more I thought about it, the more I tended toward the conclusion that this IC (when used with a single PV cell) would need "bootstrap assistance" from something like a 2016- or 2032-sized button battery, thereafter running on its own without battery support except for possibly the rechargeable battery that supports load current.

STM folks are very smart and keenly attuned to market needs. I'm sure that if it were possible to get this part to run without bootstrap assistance on a single 0.6VDC silicon PV cell they would have done so and documented their success in the IC's application note.

You and I are not the only engineers that would appreciate a single PV cell inverter solution.

[paolus]

Dear Jim,

Thank you very much for answering me. I have been struggling with the SPV1040 to achieve stepped-up voltage from low input voltage but with no success. I think that datasheet specification isn't right. I have also changed some resistors to accommodate my input according to the eDesignSuite...

However, I found in my lab a STEVAL-ISV019V1 evaluation board for the SPV1050 ULP energy harvester and battery charger. It claims to work from 0.5 V. I have tried with 0.6 V and it is working, so for now I will use it.

Thanks again for taking the time to answer me!

[APock.1]

Dear Paolus,

The STEVAL-ISV019V1 appears to be the most promising evaluation board i have come across for operation with a single PV cell. The datasheet says it is able to 'harvest energy from PV panels supplying 0.5 V ≤ VMP ≤ 2.5 V', although it also says this range can be extended from 150 mV to 5V. I understand that resistors need to be changed to adjust the Vmp/Voc ratio, but i can not see any mention of how to extend the input range down to 150 mV. Are you aware of any physical changes that have to be made, or have you tried using it below 0.5 V (i.e. at lower light intensities)?

Many thanks for any help you can give.

Regards,

Adam

[paolus]

Dear Adam,

I am sorry but I have not tried with an input below 0.5 V with this module. I will let you know if I make it, and please let me know if you achieve it!

Regards,

Pablo