Joule Thief

[MarkE]

Quote from MarkE,

"To me increased efficiency is as free as things get.  So if you get x number of lumen hours from a AA battery with one circuit, and x plus y hours with another, then the "free" y lumen hours are what count.  My colleague has developed some insanely high efficiency LED circuits that work with a single AA Alkaline cell but they are commercial developments so I cannot share them.  But he has shown me ~500 lumen hours from an LED driver circuit using one AA alkaline cell".

The relationship of pulse frequency to LED brightness is the same as voltage. Increasing DC pulse frequency can increase LED brightness the same as increasing voltage. This frequency to luminosity proportion is outside Ohm's law P=V.A. The problem is that increasing LED brightness with higher pulse frequency shortens bulb life. The 500 lumens MarkE is bragging about from his "Secret Source" is probably just burning the bulb out. MarkE posted over 4000 comments in the space of one calender year. He's burning a hole through the forum the same way!

No, LED brightness is a nearly linear function of LED current multiplied by duty cycle.  LED brightness has a very non-linear relationship to LED drive voltage.  He is getting  ~500 lumen hours from a single alkaline AA cell.  I did not state the brightness.  I did not say he was getting 500 lumens from one LED, although that is feasible for a single modern 3W LED that would require a heat sink and it is not what he is doing.  He is running his LED well within its safe limits.

[MarkE]

I doubt that you are correct.  I have many high voltage/high frequency JT's here running in my home now for over 5 years and....guess what?  No led burnout.

I am even using some commercial bulbs in my lights, like the Lights of America 24 chip led bulbs and ...they are just fine with 400 volts at high freq.  My bedside table uses 2 of those bulbs and...I have been using it every night for many years and...the bulbs still work. (still using the original D cell battery also)

Do you have any real evidence to support what you have claimed?

If so, please post it.

Thanks,

Bill

No he does not.

[synchro1]

Output (lumen) per Watt is even worse than lumen per mA. As mA increase Vf also increases so the Vf x I product increases at a faster rate per lumen than just I does. So, again, maximum lumen/Watt is achieved at low mA compared to rated mA and lumen/Watt efficiency improves with decreasing current.

[synchro1]

There's two ways to cause problems increasing lumens in LEDS, both involve running too much current through them: Firstly; By raising the voltage which raises current draw, and Secondly; Raising the frequency with the same result. Running too much current through the LED wastes power and shortens the bulb's lifespan. Most of the apparent savings from increasing frequency and cutting duty cycle come from miscalculations. There's no way to beat the peak efficiency watts per Lumen ratio that the bulbs are rated for. The bottom line is, you're better off increasing luminosity by adding extra bulbs to the array and lowering the current input. I demonstrated that in my multiple LED video:

https://www.youtube.com/watch?v=IP39OoaSQb0

[Pirate88179]

There's two ways to cause problems increasing lumens in LEDS, both involve running too much current through them: Firstly; By raising the voltage which raises current draw, and Secondly; Raising the frequency with the same result. Running too much current through the LED wastes power and shortens the bulb's lifespan. Most of the apparent savings from increasing frequency and cutting duty cycle come from miscalculations. There's no way to beat the peak efficiency watts per Lumen ratio that the bulbs are rated for. The bottom line is, you're better off increasing luminosity by adding extra bulbs to the array and lowering the current input. I demonstrated that in my multiple LED video:

https://www.youtube.com/watch?v=IP39OoaSQb0

But, I use very little current.  Only high voltage at a high freq.  This is why my lights last so many hours on "dead" AA batteries.

Now, I know this is a little bit of a parlor trick in that the leds are flashing on/off at about 30,000 times/sec.  So, if the duty cycle is close to 50%, then they are off as much as they are on.  But, our lights in our homes flash on/off at 60 times/sec and no one notices this so, I do not think of this as a real trick.

As far as calculations go...I suck at math and I only observe what my lights can do.....I do very little predicting.  If/when any of my leds actually burn out, I will let you know.  I did fry my share of leds back in my early days, the smell was terrible.  But, that was long before I discovered (not invented by me) these high voltage/high freq. circuits.

Bill