Capacitors and Resistors ?

[MarkE]

The 100uF capacitor I recommend that you put use a 6.3V or higher voltage electrolytic.  You want this connected in a very short loop from the top of the 4 turn winding to the source of the JFET.

The 2.2K resistor can be 1/10W such as an SMT 0603 size, or greater Wattage.  You will probably be using parts with leads, so 1/8W or greater is fine.

The circuit will perform best if you keep the loop of the 100 turn winding to the LED to the 1n5711 to the capacitor very short.  I would add a 0.1uF capacitor across all that again keeping the leads short.  Wiring inductance in the two loops makes the circuit noisier and less efficient. 

[Pirate88179]

Wow, this question depends on a lot of things.  All of my Joule Thief circuits run from a single AA battery and output over 400 volts.  Some in the 900 volt range.  The resistors I use are only to establish a good resonance for the circuit.  A lot of times, I use some sort of VR or trimpot so I can continue to tune the circuit and keep it in resonance as the input voltage drops.

I don't know if this helps or not but I suggest looking at the main Joule Thief topic and see what others have done with this circuit.

The only thing I use a cap for in the circuit is in place of the battery.  In that case, I use supercaps.

Bill

***EDIT***

Mark knows his stuff and can best advise you on the circuit that you posted.  (I am not sure that is an actual JT circuit)  The ones I am making can easily light hundreds of leds for a long time on a "dead" battery.  Here is an example of the Lidmotor/Jeanna JT circuit.

[MarkE]

Pirate, the circuit shown is limited to low voltages by the LED in series with the Schottky diode.  Construction quality will determine the extent of voltage spikes.  6.3V is safe for the input capacitor over a good range of construction practice.  The JFET input current is miniscule allowing the resistor Wattage rating to be similarly small.

[Pirate88179]

I am sure you are correct on all counts.  What I do not understand is why someone would want to build that circuit?  You can run hundreds of leds from other JT circuits with very low mA draw.  What would make that circuit worth building?

PS  I edited my previous post while you responded.

Bill

[MarkE]

Pirate, because a JFET is a depletion mode device circuits using JFETs can be made to start down to very low voltages.  With care down to a mV or less is theoretically possible.  A lot of people don't know this, but  there are some depletion mode MOSFETs out there with decent voltage ratings.  Those allow for harvesting circuits that can produce much higher voltages than JFETs without the losses and low gain of a BJT like the venerable 2N3055.  When you get into high turns ratios it is also a good idea to add a snubber and/or clamp to protect the switching transistor against spikes caused by the transformer leakage inductance.

I think that low voltage circuits like the JT are fun because they afford experimentation where a lot of people don't expect that a circuit can work.  With some creativity and effort people have been able to show impressive results.  If you want to try something a little different you could devise up a two stage device:  A first low power stage that provides 3V of bias to a second stage that uses a power MOSFET that switches very cleanly.