Si JFET and low input voltage DC-DC converters

Cited papers
Salah-Eddine Adami, Vlad Marian, Nicolas Degrenne, Christian Vollaire, Bruno Allard, et al.. Self powered ultra-low power DC-DC converter for RF energy harvesting. FTFC, Jun 2012, Paris, France. pp.CD, 10.1109/FTFC.2012.6231746. hal-00719861
S. Ben-Yaakov and I. Fridman, "SPICE compatible model of self-oscillating converter," 2004 23rd IEEE Convention of Electrical and Electronics Engineers in Israel, Tel-Aviv, Israel, 2004, pp. 342-345, doi: 10.1109/EEEI.2004.1361161.

[@blahblahblahblah2933]

Cool application. I was messing around with the analogous circuit with a BJT, but using an old germanium transistor to take advantage of the lower base voltage. I didn't even consider using jfets.

[@sambenyaakov]

Yes, JFET seem to be a forgotten art.

[@klave8511]

@@sambenyaakov: Not always forgotten, the variation in parameters makes it very difficult to use in manufacturing quantities. The -1v to -4v Vgs is vast. Other parameters also vary far more than a bipolar transistor. Add in an operation temperature of -40 to +80C and you very quickly choose the easier design and reliability of a bipolar. The other use for jfets is as low leakage protection diodes for very high input impedance amplifiers. I really like the solid analysis in your videos, thank you for your work!

[@sambenyaakov]

@@klave8511 Thanks

[@nwekuy]

really interesting circuit, still studying aspects of the commutator coil, there also seems to be soft switching, approaching ZVS ZCS of the FET drain. nice! also, amazing that the IC, has MPPT! in there. one final remark for curiosity, maybe or probably you know: tunnel diodes have been used as well in the very early days of solar cells, to convert single cell voltage (cells parallel). tunnel current up to 220A (Ampere!) or so, available.

[@sambenyaakov]

Thanks for inut

[@L2.Lagrange]

Very interesting. I have never used any self oscillating DC-DC converter topologies. Maybe I'll have to put something like this together.

[@sambenyaakov]

👍🙏

[@mikebrown1970]

I saw some similar circuits on Linear Tech analog series book several years ago. They suggest BF862 is the best JFET to do the job.

[@sambenyaakov]

Thanks for input.

[@vitaliyl7030]

Great video. Would there be a problem with start up if input viltage slowly builds up to higher value? Do we need min dv/dt on the primary to get this going?

[@sambenyaakov]

Thanks for the important and insightful question. Thanks to the normally ON and sufficient gain at zero Vgs at low Vds, there are no startup problems - if designed correctly🙂

[@Cydget]

for enhancement mode n channel mosfets, I know they typically fail closed after being abused ( over I^2t /over voltage). Does a jfet typically fail open under the same situation?

[@sambenyaakov]

I would think that, in general, overheat causes a short and overvoltage an open circuit. JFET should behave the same.

[@tamaseduard5145]

👍🙏❤️

[@sambenyaakov]

👍🙏😊

[@JorgeSilva-em8pf]

Dear prof. Did you consider the Depletion mode MOSFET? And, concerning energy harvesting, do you know about those "sea ​​buoy", that one which flash at night at seashore? Those buoy have one battery cell inside of just 2V and there is one electromechanical oscillator/commutator which flash on a lamp for several days. Regards.

[@sambenyaakov]

I realty don't know about D type mosfets. The crucial point is if it has a respectable gm at low Vds. About sea harvesting, yes this has been demonstrated but very complex. Thanks for conversation.

[@RaananL]

Hi prof. I think there is a missing output rectification diode in the circuits shown at 8:54 and 7:25.

[@sambenyaakov]

Nothing is missing😊This is NOT a flyback. Have you watched the video to the end?

[@BienestarMutuo]

No.