toroid joule thief circuit and LT spice

[large_ghostman]

Hi
How do you sim a standard joule thief circuit based around a toroid in LT spice? Just looking for a simple sim of say 0.4V input and to play with the number of windings to get different voltages out.
I am totally unsure how to do it in LT.

 

[alec_t]

Read the LT help FAQ regarding transformer sims. Remember that inductance varies as the square of the number of turns of a winding.

 

[large_ghostman]

what do I do about different wire thickness for secondary and primary? Or could I sim it as 2 inductors? I can measure the inductance of each of the windings?
Maybe I am over thinking all this, HMMMMM Do I actually need to sim it? might be as quick to just build and measure each one rather than sim it then build. Isnt as if its a major build. Does toroid size make much difference? Its mostly that kind of thing I am after, sorry its vague but the direction for this is also a bit vague.

 

[alec_t]

If you have data for a toroid (do you have the datasheet?) you should be able to calculate how many turns of wire are required for a particular inductance. Wire thickness and toroid size would depend on how much current you need in the windings and on the core saturation properties.
The sim would involve two inductors plus a directive such as k1 L1 L2 = 1

 

[large_ghostman]

No datasheet it was a salvaged toroid, I think its easier to just build and experiment.But I will have a go with LT and do some sims via some datasheets.

 

[alec_t]

I think its easier to just build and experiment.

It's more fun, anyway. If you have access to an inductance meter (I bet your Dad's got one!) you can wind a known number of turns onto a toroid and measure the inductance to give you a 'how-many-turns-per-uH' indication. Perhaps you could also rig up a jig to determine core saturation properties.

 

[tvtech]

Hi

Looking at LG and alec's discussion here......both you guys are exceptionally bright..not clever...just bright which oozes intelligence.

Cleverness is trying to outsmart people...Brightness is natural intelligence. A huge difference. Just cause I like you Guys and I am bored a rep for both of you .

Keep it up
tvtech

 

[large_ghostman]

Dad dosnt have a LCR meter, but I let him borrow MINE when he ask's nicely lol. I got a decent one for Christmas year before last. Can you explain the core saturation part? How do you know if its saturated? What am I looking for?
Yes I could google, but this isnt a google question. I am more interested in what I can measure and look for, my meter is a good one, it has Q and all kinds of functions. So it would be a good chance to learn a few techniques and gain some good knowledge from experimenting. I am going to desolder some different size toroids from some old ATX psu's I have. My power source will be 'Dead' batteries to start with, then around 3.3V input.
Thanks for the help, I am pretty sure I am about to learn some important stuff. Transformers are one of those thing you just use without too much thought, Knowing how they work etc will be a good basic block to learn.

 

[4pyros]

Its a fun project, with lots of good info on the web. Many people have put a lot of work into optimizing Joule Thief's to suck every bit of power out of old batteries.

 

[cowboybob]

It's also a good opportunity to discover why coupled inductors are often "polarized" (the dots displayed in the schematic symbols), an important concept when constructing the circuit(s) you are considering (others as well, of course).

 

[alec_t]

Check this out re saturation measurement:
https://www.google.co.uk/url?sa=t&r...EZWPF7YYZFQ1YN1gABcarmw&bvm=bv.63808443,d.ZG4

 

[dr pepper]

I'm not an expert on LT, however if your running a transistor on the edge of its bias you might be better building the circuit, it will probably even vary quite a bit between transistors.

As for inductors I built a inductor test jig, its invaluable for bashing your own inductors, I built ronald dekkers version but did a couple of minor changes, you can use this circuit to measure saturation current, and see how the inductor saturates, you can also measure inductance at any current.
Towards the bottom of the page:

https://www.dos4ever.com/flyback/flyback.html

 

[large_ghostman]

thanks for that

 

[large_ghostman]

Thats a really neat site!

 

[dr pepper]

Kinda usefull innit.

I put the current sense reisistor in the ground leg of the switching fet, so my 'scope ground is circuit ground rather than+.
Mine has been very usefull, esp for a couple of quid.