Joule theif not working at 0.5 v ?

[omdano]

Use a lower voltage transistor.  JFETs are ideal, Ge transistors will at least get you closer to zero.  If you use junction transistors, heating the transistor up will lower the starting voltage.  You could use that to invent the "match lite Joule Thief".

So... any JFET ? would you recommend any types or any specific ones ? (Except 2sk170 / LSK170 )

[conradelektro]

So... any JFET ? would you recommend any types or any specific ones ? (Except 2sk170 / LSK170 )

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

[omdano]

Guys , i am not talking about 50mV i am talking about 0.5 volts as in 500mV

[conradelektro]

Guys , i am not talking about 50mV i am talking about 0.5 volts as in 500mV

Then use the ALD110900 or ALD110800 it works down to 0.2 Volt (200 mV).

http://at.mouser.com/Search/Refine.aspx?Keyword=ALD110900

http://at.mouser.com/Search/Refine.aspx?Keyword=ALD110800

Still, I would go for the 2SK170 because it leaves room to go far below 0.5 Volt. If you are at this low Voltages, how long will it take before you go down from 0.5 Volt?

There is no easy way, you would not be here to ask if there was. We do not do miracles.

Greetings, Conrad

[omdano]

I am not using a battery for this one , i am going to use a constant 0.5 v power supply of my own