Thank you for some hints
Yep, I use
spice models too but for 3 elements just tried
falstad first and hopefully nothing burned so far and basic version of Joule Thief concept with diode, BC337, 1K resistor, 1.24V battery and random core worked just after soldering everything together and I got bright light from 3mm 3V diode, so not so bad
Still unsure if going above absolute VEB BC337 ratings which is 5V reverse voltage is a good idea and it is difficult avoid this if we add shunt-regulator with 12V Zener diode, but it looks like I found a way to avoid this.
I saw @T3sl4co1l your Joule Thief device and @motocoder efficiency optimisation attempts in this thread
https://www.eevblog.com/forum/projects/joule-thief-optimization-your-ideas-wanted/ , however efficiency is not critical in my case.
When "simulated" more classic basic circuit with transformer 10uH coils and 3V LED and transistor hfe 100-300 theres is NO this strange problem with transistor base reverse voltage at all, and LED current spikes are below its maximum ratings-everything looks fine:
However it looks like when we put higher inductance lets say 100uH, or higher hfe output LED current goes mad and there were above 100mA current spikes, so... added 330R in series with LED and now output curent has around 20mA spikes which I like, but... we get those strange close to -10VBE spikes
Of course we can try choose proper inductor, etc, but... something what noticed also when tried add simple 12V Zener shunt-regulator.
Thanks @bktemp removeing 100R is fine and no strange high current spikes througth 12V 0.5V Zener diode, but 100R and another second diode was there for another reason-it was my attempt to integrate this Joule Thief with 1N4148 diode with already existing simple PC817 based module which is used to triger thyristors using AC mosfets switch in spot welder, but no problem-I can by pass and short this resistor as well as not needed diode while with 100uH 1:1 trafo I've got in this simulation now nice close to 12Vgs
BUT look at this !!! Close to -10VBE
?
If we add BAT85 diode:
in series with transistor base it looks much better now and only (?) about -6VBE, but still above BC337 5VEB datasheet absoulte ratings
Of course time to try the same in spice, while I've changed additional transistor base BAT85 diode to 300mVf which is at ~10mA IF, which I fought might have sense, but I've already this circuit soldered, so adding BAT85 is not a problem and can try it in reality right now, but always theoretical attempts are interesting.
The most interesting part is now....
What do you think what causes this VBE be still below -5VBE assuming we do not change at all output stage which now fits my requirements and even under load I have decent output voltage???
When we make the same trick with LED and 330R for current limiting we get the same quite nice VBE now
In the case of LED probably better idea choose better values for transformer coil inductance to avoid any resistors if we are looking for efficiency, but in the case of shunt-regulator with 12V Zener for the moment I have no better idea, than increase slightly input voltage and add additional two schottky diodes; BAT85 on transistor base and at higher current ratings in circuit input, BUT after any caps and battery itself
For the moment in soldered prototype with 3mm whit ediode will try add BAT85, remove 27R, add series resistance to LED and see what happends with BC337 VBE.
NOTE: Without 100uF inpuit capacitor and 1.24 battery only I've got also those quite big negative VBE without additional diodes in this
falstad sim, so it will be interesting try the same in
spice