Quote from: gyulasun on September 22, 2013, 06:50:13 AM
Hi xee2,

Well, I understand what you said but I need some pondering on how a blocking oscillator's operating frequency can be set when you build it. I did build such circuits (joule thiefs etc) in the past but have never done tests how to make them oscillate above the coil's self resonant frequency.
I think basically the frequency is defined mainly by: at which frequency the coil has the highest Q (quality factor) that gives the highest active load hence highest gain for the active device, and from this gain the feedback to the base should remain a positive feedback to maintain the in-phase relationship for the continuous oscillation. 
Normally the Q of a coil increases in the function of frequency till nearing its self resonant frequency (beyond which it falls) so normally the operating frequency is lower than that.  Stray and active device inter-capacitances do reduce the operating frequency.  All what I mean is that operation frequency is "inherently" set below the coil's self resonant frequency. You or others here may see this differently of cource, I would gladly read opinions.
Of course a capacitive phase-shift can also give a positive feedback (as one requirement for continuous oscillation)  but how can you achieve it i.e. force the coil to operate beyond its self resonant frequency? Perhaps using extra capacitors at the coupling coil in the base of the transistor to help shift the phase so that oscillation may be forced higher in frequency. It needs testing of course. MAybe you have found out this already, I wonder.

Greetings, Gyula

I was only trying to point out that some of these small inductors have rather low self resonant frequencies. The ones in the link seem to be high enough (500 KHz) for most Joule thiefs, but not all small inductors may work.


The blocking oscillator works by inductive coupling between the collector and base coils. This coupling needs to have the proper phase for oscillation to occur. I would suspect that above the self resonant frequency the phase of the coupling may not be correct for oscillation. However, I have not investigated this. But, I suspect that the frequency of the Joule thief will be below the self resonant frequency of the inductor. 

Quote from: xee2 on September 22, 2013, 10:56:05 AM

But, I suspect that the frequency of the Joule thief will be below the self resonant frequency of the inductor.

Xee2:

Would we gain anything if we designed a JT to resonate at the coils self-resonant frequency?  Would this increase the output or the efficiency any do you think?  How would one test to find the coils resonant frequency?

Thanks for the tip on the small wire clipped to my test leads for probing those little pins on the inverter transformers.  I have still not got it figured out yet but, this method is better than anything I was able to come up with.

Bill

Quote from: Pirate88179 on September 22, 2013, 11:18:15 AM
Would we gain anything if we designed a JT to resonate at the coils self-resonant frequency?  Would this increase the output or the efficiency any do you think?  How would one test to find the coils resonant frequency?[/size]

I do not think you would have a Joule thief anymore if you did that. There are many oscillators that use resonators to set the frequency, but the Joule thief is not one of them (in my opinion). I do not know of any design equations for calculating the frequency of a Joule thief. The frequency depends on a lot of things - coil inductance and coupling, transistor gain, transistor bias point, added capacitances, operating voltage, and probably some more.


You can usually find self resonant frequency by sweeping input frequency and looking at voltage across coil on scope. Voltage will usually peak at self resonant frequency.


This gives some more information about self resonance >> http://www.cliftonlaboratories.com/self-resonant_frequency_of_inductors.htm[/font]

Quote from: xee2 on September 22, 2013, 10:56:05 AM

I was only trying to point out that some of these small inductors have rather low self resonant frequencies. The ones in the link seem to be high enough (500 KHz) for most Joule thiefs, but not all small inductors may work.


The blocking oscillator works by inductive coupling between the collector and base coils. This coupling needs to have the proper phase for oscillation to occur. I would suspect that above the self resonant frequency the phase of the coupling may not be correct for oscillation. However, I have not investigated this. But, I suspect that the frequency of the Joule thief will be below the self resonant frequency of the inductor.

Okay, and that is what I also meant, thanks.

Gyula

Hi folks, so does anyone have any input in regard to what i brought up earlier, that is trying to figure out why the secondary coil with capacitor and led bulb diodes are lighting in both directions.
My best guess so far, is because the secondary coil is ringing either within itself or interacting with primary coil to cause led diodes to conduct on field collapse.
Not sure if intermittently charged capacitor is adding anything, though one thing is for sure, the capacitor is benefitting this circuit greatly.
peace love light