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Using varistor instead of pot. to autom. adjust res. in joule-thief for bat.life

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Distelzombie:
I'll happily await your response, JS :D

mmagin: I don't want to fully replace the circuit. As far as I understand my circuits performance in comparison to others, it's quite great, isn't it?  ??? I don't understand the circuit very much. I would need to have a scope to finally understand it.  |O
But... I think I get one of these in order to have something to compare mine to. LTspice says my efficiency isn't particularly great, (~63%) but it isn't very accurately simulated and it also does not have indicator for light-output. (And Light over Time is really good, I think)
I also found a thread on stack exchange where someone used a 2N3819 JFET. So now at least I know that many would work fine.
Is that ZXSC300 you recommended a good one? Are there better ones? Do you know which on is "the best"?  ;D

JS:
63% ain't that bad, you have a serial diode with the LED generating losses right at the load, an oversized shottky would improve there. Then there is the transistor saturation voltage, if you could use a mosfet with low rds you improve there. The coupled inductor might have some considerable losses, etc. Adding up to 60+% is completly reasonable.

JS

Distelzombie:
I tried using shottkys. The Light output was considerably lower and it had a higher current at the LED. I'm currently using normal N4007 diodes. I think 1N4007. They worked best for some reason.

A MOSFET? Hm, are they fast enough?
If I can I buy from digikey. (They also have that IC mmagin was talking about) I just hope I can buy there without a credit-card and that they send to germany. If you say "low rds" do you mean the "Rds On (Max) @ Id, Vgs" section/column in digikey or the "Drive Voltage (Max Rds On, Min Rds On)" column?
Right now the page doesn't work anymore, unfortunately.

mmagin:

--- Quote from: Distelzombie on July 08, 2018, 09:20:34 pm ---Is that ZXSC300 you recommended a good one? Are there better ones? Do you know which on is "the best"?  ;D

--- End quote ---

I've generally been happy with my limited experience with the formerly-Zetex led regulator parts that are now sold by Diodes Inc, though I suspect there are many others, since it's the standard kind of thing for single-cell flashlights these days.  I'm sure there are even cheap ones made by Chinese manufacturers I've never heard of.

I certainly get that it is more fun to design something from scratch using discrete parts :)

Distelzombie:
What is low Rds? Is 4 Ohm considered low?

EDIT: OK there are very expensive ones with less than a milli Ohm.
This is the lowest priced MOSFET with Rds under 0.8mOhm that is also available right now. Still costs 2.25€! xD
http://www.ti.com/lit/ds/symlink/csd16570q5b.pdf
Would it work? I need to know if I'd kill it when I connect it to the JT. (Huge Voltage spikes, I assume) It's only rated for 25V max and on my breadboard the JT charged capacitors up to more than 30V. Unfortunately this is another case where I need a Scope to see what is happening.
Next one with 40V costs 3.1€ already.
http://www.onsemi.com/pub/Collateral/NVMFS5C404NL-D.PDF

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