Hualde Otamendi, MikelCruz Blas, Carlos Aristóteles de laCastellano Aldave, Jesús CarlosCarlosena García, Alfonso2025-06-262025-06-262025-05-29Hualde-Otamendi, M., De La Cruz-Blas, C. A., Castellano-Aldave, J. C., Carlosena, A. (2025). Power converter for ultra low-frequency and low-voltage energy harvesters. Micro and Nano Systems Letters, 13, 1-11. https://doi.org/10.1186/s40486-025-00229-1.2213-962110.1186/s40486-025-00229-1https://academica-e.unavarra.es/handle/2454/54330Energy conversion mechanisms present in some harvesters are only able to provide very low voltage (mV) and fre‑ quency (few Hz) electrical signals, which may also have a bipolar nature (AC). These characteristics make unusable most conventional power converters to extract from them a DC voltage. This letter describes an autonomous selfstarting ultra-low voltage and frequency AC-DC converter that can start the operation for AC signals around 25 mV, and below 10 Hz. The converter has been designed with ultra-low vibration harvesters in mind, but is also of appli‑ cation to, for instance, thermoelectric generators (TEG). The circuit is basically an oscillator driven by the harvester output, which therefore converts a low-frequency and low-voltage signal into large signal oscillation amenable for further DC conversion. The proposed circuit is based on the classical Hartley oscillator, which is modifed in a non‑ trivial confguration, and optimized to be able to operate with bipolar, low frequency and voltage driving signals. This is achieved with a minimum number of passive components and a single JFET transistor. A practical prototype has been fabricated, and measurement results are obtained, demonstrating the feasibility of the approach. Moreover, a vibration harvester with the power converter proposed has been tested in real conditions in a wind turbine.application/pdfeng© The Author(s) 2025. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made.Micro energy harvestingUltra-low input voltageUltra-low frequency operationAC-DC converterinfo:eu-repo/semantics/article2025-06-26info:eu-repo/semantics/openAccess