Raven Luni
- Oct 15, 2011
- 798
- Joined
- Oct 15, 2011
- Messages
- 798
Greetings,
I bet alot of people are sick of hearing about this, I've had a read over the previous topics here and the wikipedia stuff etc. but I'd actually like to get an in depth conversation going about the properties of this circuit, how it can be varied for more efficiency etc.
I was looking at my facebook crap the other week and one of my friends who is a scooby diver posted a pic of her new torch. The ensuing conversation with her fellow divers showed that some of these people are paying up to £500 (possibly more) for a simple light. Most of them are LED based and the more expensive ones have things like microprocessor control for temperature monitoring. What they have in common is a burn time measured in hours Of course I thought "I can build a decent light that would run for days with the change in my pocket".
And you can see where I'm going with this: Joule Thief.
I picked out some decent looking power LEDs to test with - 3 Watt cool white - tiny surface mount things packing the punch of a camera flash - currently using 3 in series and they work great my Joule Thief driver at 3V.
What I'd like to know is what properties can be changed for greater efficiency. I'm using a TIP41A with a 33 ohm resistor and a hand wound toroid (12 turns bifilar). I've found that the resistor value sets the lower dropout limit. The higher the resistor, the higher the dropout voltage, the hotter the LEDs and the cooler the transistor and vice versa. 33 ohms is a good tradeoff allowing for a small heat sink and not cooking the LEDs too much.
What effect would changing the transformer ratio have if any? I've seen examples of large secondaries used to power CFLs and such. What effect would adding a shunt regulator have? Would this result in more constant current being available and a possible need to change to a parallel configuration? I've got more questions but these will do for now. I've yet to measure the current being drawn in my circuit - I'll get round to that tonight.
I bet alot of people are sick of hearing about this, I've had a read over the previous topics here and the wikipedia stuff etc. but I'd actually like to get an in depth conversation going about the properties of this circuit, how it can be varied for more efficiency etc.
I was looking at my facebook crap the other week and one of my friends who is a scooby diver posted a pic of her new torch. The ensuing conversation with her fellow divers showed that some of these people are paying up to £500 (possibly more) for a simple light. Most of them are LED based and the more expensive ones have things like microprocessor control for temperature monitoring. What they have in common is a burn time measured in hours Of course I thought "I can build a decent light that would run for days with the change in my pocket".
And you can see where I'm going with this: Joule Thief.
I picked out some decent looking power LEDs to test with - 3 Watt cool white - tiny surface mount things packing the punch of a camera flash - currently using 3 in series and they work great my Joule Thief driver at 3V.
What I'd like to know is what properties can be changed for greater efficiency. I'm using a TIP41A with a 33 ohm resistor and a hand wound toroid (12 turns bifilar). I've found that the resistor value sets the lower dropout limit. The higher the resistor, the higher the dropout voltage, the hotter the LEDs and the cooler the transistor and vice versa. 33 ohms is a good tradeoff allowing for a small heat sink and not cooking the LEDs too much.
What effect would changing the transformer ratio have if any? I've seen examples of large secondaries used to power CFLs and such. What effect would adding a shunt regulator have? Would this result in more constant current being available and a possible need to change to a parallel configuration? I've got more questions but these will do for now. I've yet to measure the current being drawn in my circuit - I'll get round to that tonight.