Joule Thief 101

[Magluvin]

You have a significant amount of inductance in your battery lead wires...

What does the waveform look like if you scope directly across the battery?

PW

The blue trace is across the battery, in proper polarity.  Could it be that the sec winding is causing it through the off transistor? If so it would seem that the coils initial discharge is in the wrong direction to increase the voltage across the batt. Or the trigger winding through the transistor base?  The resistors is very low at the time, not 0ohm as the circuit stops oscillation, in this config anyway.  But we see the wave in the yel trace also. Thats why Im questioning it myself. But if I put disk caps across the batt the oscillating freq drops.

I will shorten the leads and see if there is a change in freq.  The shot of the single wave would show the freq of 15mhz on the blue trace if I lower the v/div 1 step, but i wanted to have the yel trace to be the same and lowering both, yel peaked above the screen and the measurements would be off. But it was a steady 15.14 mhz or so. Seems to change a bit as the battery gets used.

Mags

[MileHigh]

Seems you've constructed some sort of "resonant"
circuit there TK.  Evaluating this performance to
arrive at an explanation should be a most beneficial
exercise.  So far, well done!

Yes, in the real world we would call that a filter.  You have an excitation that passes through some kind of filter which is based on your circuit, and then you get a response in the load.

[tinman]

You are dealing more with turn off time than junction capacitance.    Is you positive going current pulse/spike also wider with all 3 diodes in the circuit as compared to just one?

By reverse current spike across the CVR,i guess i mean the same as what you call the positive going current pulse--the 3% duty cycle part that go's against the diodes,but through the LED?.

I suspect the 4007's are turning off one after another.

How can one turn off after another,as once one has turned off,then no current will be flowing through the others.


Brad

[picowatt]

By reverse current spike across the CVR,i guess i mean the same as what you call the positive going current pulse--the 3% duty cycle part that go's against the diodes,but through the LED?.

How can one turn off after another,as once one has turned off,then no current will be flowing through the others.


Brad

Good point...  possible brain fade...

So does the 4007 reverse current spike (the LED forward current) get wider as you include all three diodes or just increase in amplitude?

PW

[tinman]

Good point...  possible brain fade...

So does the 4007 reverse current spike (the LED forward current) get wider as you include all three diodes or just increase in amplitude?

PW

As far as i can tell,it only increases in amplitude.

Tried some uf4007 diodes,and result's are as TK's-to a point. If i drop the 1k resistor down to a 100 ohm resistor,i get the reverse current spike back across the CVR,but not enough to light the LED.

I tried a few of those little inductors that look like resistor's(what are they called ),and even with the fast diode's in there,by raising the frequency,the LED will light brightly-different inductor of course =different frequency.

So we have learned something here
But i am a little confused about this turn off time,as the 1n4007 data sheet's all show a test frequency of 1MHz,while here i was using only 10KHz. If it is suited to frequencies of 1MHz,then how can it not switch off fast enough for 10KHz ?.


Anyway,i think maybe you missed my post to you some time back PW,in regards to the cool joule.

I have now built the circuit using larger primary coils from transformers. This has now allowed me to place my scope anywhere over the circuit without it shutting down--it has made the circuit a lot more stable. The early CJ circuits used small high turn,high resistance air core coil's,and even toughing the base with your finger would shut it down. But with these larger coil's,i can now scope all over the circuit,and so,would like to see if it is just the miller capacitance effect at work here,or !im suspecting! has more to do with coil capacitance.

Below is the circuit (modified version,that excludes the charge battery),and scope shot from points depicted in circuit diagrams.-->Please note in the second,i have no channel offset,and have switched channels around--i do this often to make sure one channel is not playing funny buggers.

1-So how has L1 and 1.5v battery(collector/emitter junction) got around 4.7 volts across it before the transistor has switched off?.
2- How is there below 0v across L1 and battery(collector/emitter junction) before transistor has switched on?.<--This one could be explained by some sort of overshoot of L1,and where i think coil capacitance may come into it?.


Brad