Joule Thief 101

[tinman]

No in fact the resistance is not that critical in the RLC resonator because it is an active circuit where an external power source keeps the resonator resonating regardless of the inherent resistance in the resonating components.  There is no special balance with regards to the resistance in what is essentially an LC resonator.

Th Joule Thief is not an RLC circuit as I have clearly shown.  It is an active circuit that charges and then discharges a coil.  It's the charging cycle and the discharging cycle that determine the operating frequency, and there is no RLC resonator in sight.  Instead there are two L/R-type time constants that factor in to determine the operating frequency of the Joule Thief in its standard normal operating mode.

You can try to ignore what I am saying, but facts are facts.  Anybody that is interested in electronics would want to study and learn about both pulse circuits and resonating circuits and the associated need to be able to recognize and make a distinction between pulse circuits and resonating circuits.

Note that I am not talking about a hacked Joule Thief circuit here, just an ordinary plain vanilla Joule Thief that is a basic pulse circuit that switches a transistor on and off.  It's a distant cousin of a 555 timer circuit configured as a free running astable multibrator.  Likewise, a 555 running as an astable multivibrator has nothing to do with resonance.  Its operating frequency is determined by RC time constants whereas for the Joule Thief its operating frequency is determined by L/R time constants.

Like I said, you have a "fan club" and anyone interested in Joule Thieves should build a standard Joule Thief first and understand how it operates and probe it with their scope and observe the positive feedback mechanisms in operation.  Then if they want to hack into it and try to make it resonate then more power to them.  The critical point being that if they are claiming resonance then they need to identify the L and C components that are exchanging energy back and forth and show that in action.

MileHigh

Th Joule Thief is not an RLC circuit as I have clearly shown.

How did you ever come up with that MH ?.
The JT is most certainly an RLC circuit.


Brad

[Magluvin]

Thanks for taking the time to do those tests TK.

Mags

[MileHigh]

How did you ever come up with that MH ?.
The JT is most certainly an RLC circuit.

Brad

Really?  Take a look at the attached diagram.  This is an intentionally simplified explanation showing the two principal processes that determine the operating frequency of the Joule Thief that ignores the battery voltage and the positive feedback transistor switching process.

There used to be a good explanation on the operating frequency of a Joule Thief that went into quite a bit of detail on Wikipedia but apparently it was disputed because it has since been removed.  Here is a link that discusses the inductance being a prime factor with some information from the older version of the now-modified Wikipedia page:

http://www.elperfecto.com/2011/01/22/toroidal-inductors-number-of-turns-affects-joule-thief/

Feel free to make your case for a Joule Thief being an RLC circuit.

MileHigh

[Magluvin]

Just made a quick sim of the right and wrong circuits running simultaneously. The circuits do work. The left is what I had labeled as 'wrong' and the circuit on the right is, well, 'right'

The scope shots are source(1.5v batt) pk power traces to the left, top is 'wrong' and bottom is 'right'. And the traces on the right are the leds, top 'wrong' bottom is 'right'.    The power traces are peaks, not average power. So we will leave it up to TK to determine which circuit has the advantage of pulling less from the source. He has shown a higher lux from the leds with the 'wrong' circuit so far. Im not sure if that is a noticeable difference in brightness to the eye.

The 'right' circuit has a higher running freq.   

If you slow down the sim control slider, the 'wrong' circuit it seems the transistor never really turns off and always draining the source, along with the led draining the source when it is on. And the 'right' circuit the transistor does turn off and the led does not drain the source when on.

Here is the code for the sim. For some odd reason the codes dont always provide the scopes as what shows when the code is exported. I retried the code and it did this time.


$ 1 5.0E-6 0.625470095193633 50 5.0 43
t 416 400 496 400 0 1 -1.403784455736806 0.7049612942489206 100.0
w 496 416 496 448 0
w 496 448 336 448 0
169 416 240 496 240 0 1.0E-4 1.0 -0.001746210276144522 1.2763726782599143 1.2763726782599143
w 496 240 496 208 0
w 496 208 416 208 0
s 336 208 416 208 0 0 false
v 336 448 336 208 0 0 40.0 1.5 0.0 0.0 0.5
r 384 304 384 400 0 100.0
w 496 384 496 304 0
w 496 304 560 304 0
w 496 448 560 448 0
162 560 304 560 448 1 2.1024259 1.0 0.0 0.0
w 416 208 384 240 0
w 384 240 416 304 0
w 416 240 384 304 0
w 384 400 416 400 0
w 784 400 816 400 0
w 816 240 784 304 0
w 784 240 816 304 0
w 816 208 784 240 0
w 896 384 896 304 0
r 784 304 784 400 0 100.0
v 736 448 736 208 0 0 40.0 1.5 0.0 0.0 0.5
s 736 208 816 208 0 0 false
w 896 208 816 208 0
w 896 240 896 208 0
169 816 240 896 240 0 1.0E-4 1.0 5.1958437552457326E-14 0.31968522644013664 0.3196852264401375
w 896 448 736 448 0
w 896 416 896 448 0
t 816 400 896 400 0 1 -4.049226601125407 -0.5211382639894485 100.0
w 896 304 944 304 0
w 896 240 944 240 0
162 944 304 944 240 1 2.1024259 1.0 0.0 0.0
o 7 1 1 291 4.676805239458889 9.765625E-55 0 -1
o 23 1 1 291 4.676805239458889 9.765625E-55 0 -1
o 12 1 1 35 5.0 9.765625E-5 1 -1
o 33 1 1 35 5.0 9.765625E-5 1 -1


Mags

[Magluvin]

It seems the code I posted has the resistor at 100ohm.  Change to 500ohm to show what I posted in the pic.. 100ohm here tends to run the circuit in the greater than 1 watt range. Trying to stay some what in bounds.  The transformer is 1:1 100uh.   Didnt play with transistor or led settings.

Mags