Joule Thief

[resonanceman]

I had  an idea
I wonder if anyone else  wants to play around with it.
I am thinking  that  a resonant circuit in a JT could  be helpful
It may help  the JT run on much lower input voltages.

I have tried adding a cap in parallel  with the coil going to the base.
Although it can be done by connecting the cap to either end.....so far it looks to me like it works  better  if  I untwist  the ends of the JT primarys  and connect the cap there.

In theory...... once it is running (the secondary powering LEDs )  the LEDs should  be brighter with the cap than without it.

In my  first tests the only cap that did this  was a 1uF tantalium ......a 1uF polypropylene cap was no better  than any other cap I tried.
With the tantalium cap it was slightly brigher with the cap than without ......but only slightly

It is usually necessary to short  across the cap to get the JT started.

My first tests were done on a candy cane  coil.........4 turns through the  center for  primarys.........20 turns on each of  6 toroids.
I am not sure if candy cane coils  are ideal for this.....but it was what I had  handy.


I am thinking  more turns on a primary might  be helpful for  this particular circuit.

gary

After testing a little more..........my 1uF tantalium is still the only cap that makes the LEDs  a little brighter  connected  than unconnected........but  the brightness fades in a minute or so...... and  even though it is  brighter....the starting voltage is about 10 V less than without the cap...... I am measuring the voltage across my LED array.
The voltage then drains away another 10 V or so  before it levels off.
As it does this  the LEDs grow dimmer in step  with the falling voltage.

I can't  check the input  power........I fried my meters that can read that.

gary

[crowclaw]

@FreePow,

As Mr. Mag suggested go for a good used one with a decent spec and bandwidth. I am fortunate to own various pieces of good test gear including a PC scope. you can save waveforms as a file and refer to them from a folder or forward on, mine built in the UK (which is my home land) also features both a digital meter and frequency spectrum analyzer. A spectrum analyzer on it's own may not necessary be that useful due to the harmonic content of the JT's output waveform. Scopes generally are looked after so you should be able to get a decent instrument with a good spec cheaper.

[MrMag]

@FreePow,

As Mr. Mag suggested go for a good used one with a decent spec and bandwidth. I am fortunate to own various pieces of good test gear including a PC scope. you can save waveforms as a file and refer to them from a folder or forward on, mine built in the UK (which is my home land) also features both a digital meter and frequency spectrum analyzer. A spectrum analyzer on it's own may not necessary be that useful due to the harmonic content of the JT's output waveform. Scopes generally are looked after so you should be able to get a decent instrument with a good spec cheaper.

How do you like the PC scope? I've always been interested in them. The nice thing about them is that once you have the scope interface the rest is software. Opens a lot of possibilities. Not to mention the snapshots and file saves. Does it perform as well as a CRT based unit?

[crowclaw]

How do you like the PC scope? I've always been interested in them. The nice thing about them is that once you have the scope interface the rest is software. Opens a lot of possibilities. Not to mention the snapshots and file saves. Does it perform as well as a CRT based unit?

Yes it's a fantastic tool... you can closely sample intricate waveforms and freeze frame and save the data for future analysis. Mine is a few years old and performs impeccably. Pico technology is the company over here that market a range of  PC scopes and various add ad dons. Several other companies also market similar. I have posted several screen shots here, taken with this tool. Not sure of current prices for these. Where you score with this type of instrument is comparing waveforms while carrying out  experimental work especially on JT's however!!!! remember to safely attenuate the input signals first. One trick I recommend is to clip the probe lead onto the insulation of the JT/s high voltage pulse output wire rather than making a direct electrical connection, you will have to increase the scopes input sensitivity. A scope is really essential for any serious electronics hobbyist and an absolute must for these oscillator / pulse circuits... the wider the bandwidth the better. Glad to help

[Pirate88179]

I agree totally. I followed MrMag's recommendations a while back and found and obtained a Tektronix model 2213 60 mhz dual channel scope with manuals and got 2 new probes on Ebay for $150.00 total.  Best purchase I ever made.  This is a very good quality instrument and works very well.

Of course, I am still learning how to use it properly but, I am getting there.

Bill