Joule Thief 101

[tinman]

Im getting high enough freq levels at very low battery levels that you cannot see the blinking with the eye. No way. I havnt taken a battery ALL the way down yet to see if I can get it to blink. Will run one down hard to see, soon.
But as far as I can see so far, I dont think it is circuit operation that is giving visible blink, unless the windings were more than we have been playing with here, meaning way more inductance, low freq. Other than that, Id bet on battery weakness at the time of slow visible blink.

Mags

Hmm. This is the second time Ive heard of the led going into blink mode. Smoky said it once earlier.  Is that when the battery is super low? Because it seems to me that would indicate the battery is at a level that it needs some refresh time before being able to fire the transistor again.

That is correct Mag's--the battery needs time to recover to a voltage where it can start to switch on the transistor again. If the battery voltage has not recovered enough by the time the next cycle is ready to start,then the transistor will not start to conduct,and you skip a cycle or two until there is enough voltage recovery on the battery. This you can test using a cap that is fedd by a battery or PSU with a resistor between the two.

You can also decrease the required supply voltage,and still have the JT running,by decreasing the base resistance. This i will cover in my next video.

Brad

[tinman]

Here is the next video on bench testing the JT circuit.

This comment posted on my video from a viewer.

the joule thief schematics you are using is more like a boost converter, the classic Joule Thief has the LED connected  in parallel to the coil in reverse to use just the inductive spikes, of course the voltage of that battery is not enough for the LED voltage conductivity, but it has a different approach to the circuit.

Just go's to show that there is not just one common JT circuit.

Anyway,we look at the base current in this video,and we can see the effects it has on the operation of the circuit.

https://www.youtube.com/watch?v=72BqF8bkk-k

Brad

[Magluvin]

Here is the next video on bench testing the JT circuit.

This comment posted on my video from a viewer.


Just go's to show that there is not just one common JT circuit.

Anyway,we look at the base current in this video,and we can see the effects it has on the operation of the circuit.

https://www.youtube.com/watch?v=72BqF8bkk-k

Brad

lol. Like I said way earlier before I had built my first Jt, the led across the winding seems a better choice as to not include the battery current in the led drive loop, as that would deplete the battery at all times while the circuit is running, vs having a real off time while the coil dumps to the led.

Mags

[tinman]

     

   

MileHigh

I am going to have to take my statement back and qualify it.  On closer inspection of your scope shot I can see that indeed the base waveform is showing that the transistor is ON and you are correct that the level is 800 mllivolts.

Well this is good

What are the root causes of the misunderstanding?

Oh here we go

The first is that I wasn't observant enough to see the fact that in your close up shot that the trace is just hugging a point above the zero volt line.  I thought it was zero volts, not hugging just above zero volts.

I thought

A not too distant second factor is that your presentation skills are generally very poor and it's easy to get thrown off because of that.

Ah-there we are,the big old switcharoony--now it's my fault because of your lack of observing skills.
Point 1--in the video,i went through all the scope setting value's.
Point 2-the screen shot you posted yourself has all these values clearly presented on that screen shot. The VPD on CH1 clearly show's a value of 5volt's,meaning that 800mV would be just above the zero volt line. The Vmax on CH1(800mV) is also clearly visible in the calculated value's on the right hand side of the scope shot.
Point 3- i told you all this in a previous post--but still you were lost.

A third factor is in your original clip it looks like a zero-volt baseline with a big positive spike - sloppy presentation and poor communication skills come back to haunt you.

It is your lack of being able to interpret and observe what the scope is showing you,and what the scope settings are,that is being the cause of all your drama's.
No one else here had trouble understanding what was going on in the video.

The circuit will run just fine on low voltages when the base resistance is set to the !correct! value--another reason that a fixed base resistance is no good.

In Magluvin's capture it takes about 30 microseconds for the LED to discharge and it runs at 4.2 kHz with a total period of about 238 microseconds.

Is my setup exactly like Mag's ?

There is no reason that your setup shouldn't have comparable timing.  You are supposed to get a nice clean "crisp" set of waveforms like in Magluvin's capture.

Are you serious
Do you think that two different LED's will work in the very same way?
Do you think that two different core's will operate in the same way.
What about different transistor's?
What about different numbers of turns for each coil,or the wire size used?.

How you can say that the two different circuit's will/should operate very close to the same is beyond me.
Like i said MH,you really are not well versed in JT circuit's.
The fact that you do not know why the transistor stays on longer,and the frequency lower's when the base resistance is decreased,truly shows you have so much left to learn.

Facts are facts MH,and your fairy tails have been proven to be just that--fairy tails.


Brad

[tinman]

lol. Like I said way earlier before I had built my first Jt, the led across the winding seems a better choice as to not include the battery current in the led drive loop, as that would deplete the battery at all times while the circuit is running, vs having a real off time while the coil dumps to the led.

Mags

Exactly
And i too found having the LED across the L1 coil to be much more efficient.
But having the LED across the base/emitter put's energy back into the battery

Brad