Joule theif not working at 0.5 v ?

[TinselKoala]

Sorry, many people tried to find a replacement for the 2SK170, all transistors found were worse. In practice there are hardly any applications for a circuit below 0.5 Volt. To do anything useful below 0.5 Volt the current has to be very high. In general it is better to have a higher Voltage (at least 1 V or 3 V) and less current because the components do not heat up so much.

I did some tests with the transistor ALD110900, but it is much worse than the 2SK170 and more expensive (see the attached circuit).

So, if you want a transistor that switches down to 50 mV, I am afraid you have to get the 2SK170. I know, it has become difficult to get, try eBay.

http://www.ebay.com/itm/2SK170-TOSHIBA-FET-Transistor-N-Channel-QUAD-MATCH-4PCS-/270914931710?pt=LH_DefaultDomain_0&hash=item3f13c9cbfe
http://www.ebay.com/itm/2SK170-GR-Toshiba-JFET-Transistors-/300881599819?pt=LH_DefaultDomain_0&var=&hash=item460df0dd4b

Greetings, Conrad

I don't know why people think that the 2sk170 is "difficult to get". There are lots of advertisers with lots of stock, genuine Toshiba stock too. Prices I've seen vary from very low like 20 cents each to very high, like several dollars for a matched pair. You can get lots of 10,000 in original Toshiba packaging from EBay. Or you can get individual ones without Toshiba branding for 20 cents each.

http://www.futurlec.com/Transistors/2SK170pr.shtml


I've got one JT here, the DALM circuit with four blue LEDs _in series_, that oscillates (without lighting the LEDs) down to around 360 mV, but needs about 610 mV to actually light the LEDs. It uses a BC337-25 or a MPSA18 silicon BJT and has a 1:1 toroid winding ratio. (20+20 turns).

[TinselKoala]

I have a handful of 2n5163 FET transistors that I pulled from some surplus MRI scanner boards. I haven't tried one in a JT yet but according to the data sheets they might work nearly as well as 2sk170.

Has anyone tried the 2n5163 yet?

[omdano]

What about the all forgotten germanium transistors ?
don't they work as low as 0.2v ?

[conradelektro]

What about the all forgotten germanium transistors ?
don't they work as low as 0.2v ?

Look at that search http://at.mouser.com/Search/Refine.aspx?Keyword=germanium+transistor and you will see that the modern germanium transistors are optimised for high frequency (GHz) not super low Voltage.

0.5 V seems to be a little bit too low for making a LED light up with a Joule Thiefe type circuit, unless you find something like the 2SK170, and the only one coming close some one found is the ALD110900.

There are older Japanese transistors, but they are realy hard to get.

I would say you put your "constant 0.5 V power supply of your own to 0.7 V" and you are out of trouble, almost any transistor will work.

There is a post by magpwr which describes the found transistors, but they are not available any more:

http://www.overunity.com/13175/25mv-joule-thief-powered-by-peltier-merely-using-our-body-heat-free-energy-247/msg350815/#msg350815

You can go through that thread (only 11 pages) to see yourselfe what has been done then.

Greetings, Conrad

[Vladokv]

The germanium transistors work at 0,2V flat. At that voltage led is not very bright. I will tomorow post pictures. One strange thing also ocurs - joule tief with germanium transistor don't work at 1,4 - 1,5v, don't know why. Work with more and less but not with 1,5v exactly