Joule Thief

[Farmhand]

Here is a web page that describes a 0.5 volt to 5-6volt booster circuit.

http://www.discovercircuits.com/H-Corner/05-6-con.htm

Quote from page.

It turns out that TI's 74AUC family of parts can work down to about 0.45 volts. I tried one of their single schmitt trigger parts and found I was able to make on oscillator function nicely at 0.5 volts.

I was thinking of trying a CD4049 to see what it could operate at, I have some 74 parts but not many,

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[MarkE]

A 74, 74LS, etc 5V series TTL or 4000 series CMOS will not work. 

The key to Dave Johnson's circuit is the ultra low voltage logic gate:  Digikey P/N   296-13169-1-ND  This is one gate in a package the size of an SOT-23 transistor but with five leads instead of three.

http://www.digikey.com/product-detail/en/SN74AUC1G04DCKR/296-13169-1-ND/484306

http://www.ti.com/lit/ds/symlink/sn74auc1g04.pdf

The device is rated for a power supply voltage down to 0.8V, but will go lower.

[Farmhand]

Yeah that part is the one to get and should be cheap 57 cents each or 40 cents each if you get 10.  With one of those parts we
should be able to make an oscillator similar to the one below but run it from less than 1 volt.

I've made an efficient oscillator circuit from a CD4049 chip and it works ok at 2.5 volts but won't work much lower.

After adjusting it a bit I got about 90% efficiency lighting 2 x 5 mm LED's from the 2.59 volt supply. I knocked off 0.05 volts from
the output so it didn't look so efficient, hahahahaha see the shot says 8 v.

The input was 3.3 mA at 2.59 v = 0.00855 W. Input fairly smooth. Measurements done with an accurate DMM and current sensed
across a 1 Ohm resistor.

The output was 1 mA at 7.95 v =  0.00795 W.  Output was DC in a cap as the shot shows.

0.00795 w / 0.00855 w = 93 % efficient. LED's were bright enough to leave dots on my eyes. 

At other less than ideal adjustments I got consistently 60 to 70 % efficient.

First shot shows the collector waveform in yellow and the capacitor voltage that the LED's are running from in blue,
8v across 2 x 5 mm LED's.. I went for zero volts at the collector switching in the first shot.

Second shot is the oscillator signal at the capacitor Blue trace, (second gate of three) and the Base drive in Yellow.

Third shot show the frequency backed off and the coil ringing.

Fourth is the circuit running, the capacitance is 200 pF and I set up the adjustable circuit from the CMOS Cookbook,
the right pot determines the output low time and the left pot determines the output high time, this can be reversed
by using another inverter gate.

The high time pulse output can go to as narrow as 1 uS to over 90% duty and the frequency from 25 kHz up to 180 kHz as it is.

I used only three gates on the bottom side of the HEX buffer.

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[Farmhand]

Here's the whole show almost. I made a simple JT with a few extra turns on the base trigger winding and used 1 K resistance. It's working about 40 kHz and boosting the 1.2 volts to 5.8 volts for the LED driver which is now driving 3 LED's with 14 volts. 

What a hoot.

First shot is the JT collector wave form and the final LED voltage.

Second one is the CMOS driven transistor collector wave form, (can use mosfet now "logic level").

and the set up. 

Interestingly the LED from ground to base is lighting up, ( it's got the end that usually goes to the positive going to circuit ground and the other end to base,  if I put a diode there it goes up to a higher frequency.

EDIT: It works better without the LED and 2.2 k base resistance, now it's boosting 7.6 volts for the other circuit.

Added circuit so far, I'll try to see how low it drains the battery to.
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P.S. Final circuit could have a three terminal output or transformer output. A three terminal output would have the circuit ground the output diode and the positive rail available to use as outputs. if we want to charge a battery that is a lower voltage than the supply voltage we can connect by the it negative to the positive rail of the circuit and charge from the output diode, if the battery to be charged is more than the supply voltage or we want to dump the cap into a load or just run LED's ect. we can connect the load by the negative to the circuit ground and charge from the diode/output capacitor. Then a divided voltage could control these logic devices to some degree. There is still three more logic gates on the CD4049 HEX buffer. 

The low voltage part that Mark.E linked to might only have one or two gates or "Schmitt" triggers (didn't look yet ) so we might need several. I'll try to get 20.

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[TinselKoala]

Note that in "CMOS osc 3" you have a very clear ringing that has a frequency very near 400 kHz. This is the natural resonant frequency. At present this is a loss, as power  sloshes back and forth dissipating a little on each cycle and the amplitude of the ringing diminishes to zero before the next "push" happens.