Joule Thief 101

[tinman]

   



 

The clip is a complete disaster and proves nothing.

MileHigh

The fact that you dont understand what is going on in my video,and what the scope is showing you ,is scary. Are you truly telling everyone here,that you cant work out if CH1 is inverted or not-->really  . Do you really not understand as to why there is a voltage spike across L1 when the transistor become's open? 

Yeah, sure it was inverted.... or was it inverted?  If it wasn't inverted, how do you get somewhere between a 10-volt and and 16-volt spike across a transistor base-emitter junction?

You dont.

If it is inverted like you claim then how do you maintain somewhere between 10 volts and 16 volts across a transistor base-emitter junction?

What do you mean maintained . It is only there when the transistor becomes open. When the transistor is switched on,we have only the base voltage of 800mV

Look at the crappy zoomed-out waveform capture from your clip that isn't even capable of showing the waveforms properly because they are grotesquely undersampled and compare that to the nice clean scope capture that Magluvin did of a Joule Thief operating in normal switching mode with a nice zoom-in on the actual switching cycle so we can see what is going on.  We are back in "communication-skills-issue-elephant-in-the-room" mode for you.

Perhaps you should take this up with Poynt,who taught me to fit as many samples as possible in the screen,so as to gain accurate measurement readings from the scope.
You are a big peanut--that's for sure.

You comment on the high-voltage spike in your clip and just walk past that totally wonky measurement like a zombie.

It is not a wonky measurement. It only looks wonky to you,because you cant work out what is going on,or why it is there

I can't be 100% certain from your foggy clip, but all of the indicators are pointing to the conclusion that your Joule Thief setup is running in wonky spastic high-frequency mode

For a start,the frequency is quite low for a JT circuit. Mag's has had his running up in the 100s of KHz range.

and the base-emitter scope channel is not inverted and there really is a super-high voltage spike across the base-emitter junction of the transistor.

Oh dear
Look at the spike from L1 that is driving the LED--dose that tell you when the transistor is off?
Look at the spike on the yellow trace--is that in line with the spike on the blue trace?
Dose this now tell you that the spike on the yellow trace is during the off time of the transistor?
Are you getting the idea now that the yellow trace is indeed inverted?,and why there is such a large spike on the yellow trace.
Are you learning now?.

 

Why would you even put your probe across the base-emitter junction when there is so much more information to be learned if you put your probe on the output of the feedback coil?

Why would we not include the VR,when it is the effect of the VR we are looking at?
Why do you jump in so quick,when you know there is more video's to come--hence the title has PT 1 in it.

You have a pretty big toroid so why is your setup running somewhere between 20 kHz and 30 kHz when Magluvin's ran at 4.2 kHz?

Well thats a stupid question if ever i have heard one.
Why dose my large car go faster than my neighbours small car?

That's what you get when your Joule Thief is running in some unknown spastic high-frequency mode.

Looks to be running quite fine to me. But i guess it may look strange to you,because everything is suppose to be just as you picture it in your head--hey MH
An odd comment from some one that dose not even have a JT,or has no idead as to how different transistors may make things operate differently.

In other words, your "demonstration" is a total fail and a miserable embarrassment considering the fact that you have been doing this stuff for six years.

I know you must be peeved MH,finding out you were wrong once again.
But i would think that the embarrassment you are feeling,is actually your own. I mean-not being able to tell if a channel is inverted or not,when you have a second channel showing you the off period of the transistor,must be a big blow for some one that prides them self in knowledge of the standard JT. Also not understanding as to why there is such a large spike at the base/emitter junction when the transistor becomes open,must also take a big hit on that pride of yours.

Then there is the fact that i have posted many video's-even on this thread,showing the LED being lit from the emitter/base during the off time of the transistor--but still you dont get it.

Face it MH,you have had another flop-->in many areas this time.


Brad

[tinman]

Yes, one can "assume" that is what is happening and use what is observed as a proxy for base current.  My point was that nowhere is base current itself being directly measured or observed in the video.



The base current, however, must be measured in the base leg circuit and does not require a separate CSR (although you could indeed use a separate 10R in series with the base as you suggest).



PW

As well, it is incorrect to state that you are varying the base voltage when adjusting the VR.

That is in relation to the switch on time between partially on and fully on. This is only during the lower supply voltage ranges,and is where the !transistor switching on harder! part of it was to come into play. As we know,the 2n3055 needs around 700mV to switch on fully,and if the battery voltage is down to around 400mV,then the transistor will be only partially on for a very brief moment until L1 starts to induce a higher current flow through L2. This i will show in the next video.

You originally used a rather large 10R in the emitter leg as a CSR for measuring emitter current.  However, resistance inserted into the emitter leg will produce "degeneration" or "negative feedback" which effectively reduces the transistor's gain.  If your goal is to stabilize the LED current as Vbatt varies, you might consider experimenting with increased degeneration (i.e., a larger emitter resistor).  If maximum efficiency or minimum Vbatt operation is the goal, this would be less desirable.  To measure emitter current, use of a smaller value emitter resistor is advised to reduce the effects of degeneration.

Yes,i understand this,but at these low power level's,a lower value resistor shows a very noisy trace on the scope. It was my intention to use a larger value in order to get a good clean trace on the scope for accurate measurements.

All you need to know is what the Vdrop across the VR is and the resistance value the VR is set to.  The use of the separate 10R as a CSR as you suggest would, however, allow you to measure the base current real time without needing to know the VR's set value.

This is the plan for the next video.

Thanks for your input PW



Brad

[tinman]

 author=MileHigh link=topic=8341.msg478111#msg478111 date=1458695560]


Look at the crappy zoomed-out waveform capture from your clip that isn't even capable of showing the waveforms properly because they are grotesquely undersampled and compare that to the nice clean scope capture that Magluvin did of a Joule Thief operating in normal switching mode with a nice zoom-in on the actual switching cycle so we can see what is going on. 


MileHigh

Whine ,whine,whine.

Below is the expanded view--of the same circuit running on a 600mV supply voltage.
Dose it look that much different from Mag's ?.
I have CH1 now around the correct way--just for you MH.
Dose it make sense now?--Is this good enough for you?
Is my circuit running in some sort of spastic mode-as you put it?.
Can you understand the high reversed voltage spike between the emitter/base junction now?

Is there anything else i can help you with?.

[MileHigh]

author=MileHigh link=topic=8341.msg478111#msg478111 date=1458695560]


Look at the crappy zoomed-out waveform capture from your clip that isn't even capable of showing the waveforms properly because they are grotesquely undersampled and compare that to the nice clean scope capture that Magluvin did of a Joule Thief operating in normal switching mode with a nice zoom-in on the actual switching cycle so we can see what is going on. 


MileHigh

Whine ,whine,whine.

Below is the expanded view--of the same circuit running on a 600mV supply voltage.
Dose it look that much different from Mag's ?.
I have CH1 now around the correct way--just for you MH.
Dose it make sense now?--Is this good enough for you?
Is my circuit running in some sort of spastic mode-as you put it?.
Can you understand the high reversed voltage spike between the emitter/base junction now?

Is there anything else i can help you with?.

Yes, that pretty much confirms that your Joule Thief circuit is running in some wonky spastic oscillator mode.  The observed pulse is a mere five microseconds which is way too short.  The transistor is supposed to be ON both before and after the LED ON pulse, and we can clearly see that the transistor is OFF before and after the LED ON pulse.  So you are absolutely running in some wonky spastic oscillator mode.  You failed to get the circuit to run properly, and your own expanded scope trace is clearly showing you that the circuit is failing to operate like it is supposed to and yet you gloat.  The problem is right in front of your face and you don't even see it.

It's just one never-ending "Keystone Cops" misadventure with you.

What is really happening in your clip?  I can tell you on a top-level without digging into the nuts and bolts of the circuit operation.  The potentiometer is acting like a frequency adjustment for your wonky oscillator.  As the frequency lowers, you can see the duty cycle for the LED ON vs. OFF does not change.  So with a lower frequency, presumably there is more time for current to build up in the main L1 coil, and therefore you get a higher peak current through the LED and therefore a brighter LED, although the duty cycle does not change.

So it's the potentiometer acting like a frequency control, giving the main coil a longer time period to energize and build up current, that results in the LED getting brighter.  That has nothing to do with the normal switching operation of a Joule Thief.

The clip is a farce.

MileHigh

[MileHigh]

Brad:

The fact that you dont understand what is going on in my video,and what the scope is showing you ,is scary.

More like after six years of bench experimentation and talking electronics, and trying to sound authoritative about the Joule Thief circuit, it's scary that you couldn't even build one and get it to operate properly.  It's double scary that you didn't even notice or try to check to see if it was running properly.  It's tripe scary that you gloat and insist that you got it right when it is painfully obvious that you got it dead wrong.

Perhaps you should take this up with Poynt,who taught me to fit as many samples as possible in the screen,so as to gain accurate measurement readings from the scope.
You are a big peanut--that's for sure.

Put your brain in gear and make the proper decisions to present your data properly and make a conscious informed intelligent decision for when to look at multiple cycles for better averaging, and for when to look at a close up of a waveform.

What you should do is back up and get your Joule Thief to work properly before you do anything else.  The long lengths of wire coming off of the toroid are probably not helping.

MileHigh