To pulse or not to pulse?...and others...

[papasan]

so, like alot of people that find there way here, i'm fairly new at electronics in general and LEDs in particular. and so, what i'm trying to do is make the ultimate cicuit (aren't we all?) and a little help may make it alot easier. i'm interested mostly in the white nichia type leds (3.6@20ma). i'm extremely interested in effieciency (half the reason to use LEDs) which the few helpful books i've read parts of talk nothing about. it seems that one nichia will run just fine off of a 3D power supply (fresh ones, ~4.5v) with no resistors, so i plan to use that so i won't have to use any power sucking voltage limiting resistors.

to pulse or not to pulse (maybe oscillate is a better term)? is this more effiecient in the end? don't you have to pulse way above what you would feed a constant circuit, plus you have to feed the circuit. so does it work out better (less power used) in the end to get the same light?

and a question about diming. just a potentiameter or rheostat in-line is a big power drain (if not fully open), yeah? what about a pot with a transistor control, does this limit the drainage somehow? i feel for efficiency's sake you need to have a dimmer circuit in there (why put out 8 candelas when 4 will do?) but i want to waste as little power doing it as i am able.

so if i put both of these together into Oddone's 555-based curcuit i would assume that this would be more efficient than these two functions seperated out.

after i get this part going i want to get into the step-up circuit that's going on in a different thread.

imagine a 1AA flashlight with one of the new 18 candela LEDs that's dim-able and lasts for hours (days?). heaven.

 

[Chris M.]

imagine a 1AA flashlight with one of the new 18 candela LEDs that's dim-able and lasts for hours (days?)

Sorry to spoil your dreams but that isn`t possible. The new leds require a regulated supply of about 3.6 volts at up to or over 350ma so even with the most efficient inverter or pwm dimmer circuit you won`t get too much runtime from 1AA battery. Probably under an hour if you were stepping up the voltage. They would lend themselves nicely to higher capacity lights like 3C and up, and probably those nifty little 123 lithiums that SureFire (and others) lights use too.

I`m not really familiar with the circuits you mention so can`t help much further. However I reckon a transistorised dimmer would waste just as much power as a large pot would, the only advantage is the fact that the power is handled by the transistor not the delicate carbon track of the little pot. What you need is a variable pulse-width-modulation circuit but I`ve not looked into their operation too much yet, sorry. Maybe that is what oddone`s circuit is like (my internet`s misbehaving and it won`t load properly- I`ll try again later)

 

[Go Go Gadget Flashlight]

Chris, you nailed it!

Oddone's LED driver circuit is PWM, based on a 555 timer IC and a Mosfet transistor.
Very cool, but much too bulky for a small flashlight application.

Papasan, I too think that resistors are a waste. If you need voltage regulation, PWM is the way to go.

Obviously, the easiest way is to match the battery voltage to the LED rating. When that's not feasible, PWM is the most efficient way to regulate power to the LEDs (that I know of...).

Oddone's circuit looks like just the ticket as long as your source voltage is a bit higher than the LED(s) demands.

Remember though, for higher voltage battery projects, you can always wire the LEDs in series. Two 6v lithiums should power 3 Nichias in series quite well.

 

[papasan]

thanks for the replies. still dunno why pulsing is the way to go over conventional dimming, but i'll do some more reading and try to figure it out. Oddone's circuit is fairly bulky, especially for a single cell flashlight. Perhaps there's other opinions or other ways which i haven't learned of yet.

Chris: i wasn't thinking hours on full blast, but dimmed down quite a bunch. according to the other thread discussion these new LEDs are ~3 times more efficient than the nichia LEDs, so even at comparable light output they should last longer, yeah? of course this is all conjecture until a few people actually get there hands on some.

 

[phyhsuts]

Perhaps I can help. The reason a PWM circuit is more efficient than a normal (linear) regulator (which the resistor is in an uncontrolled sort of way) is that they control the voltage or current not by changing its value as such but rather depend on the principle of averaging. To reduce the AVERAGE voltage at its output it just leaves the electronic switch on for a larger proportion of the time. For example, if the battery voltage is 12V and you want 6V, then you let the switch be on for half the time. The average voltage is then 6V. The "time" we have been refering to is the "period" of operation of the PWM circuit. This typically goes from 50,000 Hz to 500,000 Hz for low power commercial ICs. For interested individuals, I can supply circuits that uses these ICs for LEDs. Just email me at [email protected]. Let me know what you want. I cannot promise a solution, but we can often get close.

 

[Badbeams3]

I believe the Photon III will be using a pulse type curcuit. I read somewhere that if you spin it on a string you will see it flickering (on low and medium power) but otherwise it will not be noticable.

 

[vcal]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by KenB:
I believe the Photon III will be using a pulse type curcuit. I read somewhere that if you spin it on a string you will see it flickering (on low and medium power) but otherwise it will not be noticable.<HR></BLOCKQUOTE>

yet anothercrude way to tell is to (on low power): shine
the light at a running fan inthe dark-u can "see" the blades look like they're going backwards.
-Or, with the light turned on, hold it next to an AM radio that is off station-you'll hear th RF noise..
The Eternalight products r that
way...:O

 

[**DONOTDELETE**]

the eternalights pulsing is quite noticeable to me in many of the dim modes, but i love it just the same

 

[papasan]

just in case anyone cares =) found this chip that looks like it will do everything but take the trash out...

http://dbserv.maxim-ic.com/quick_view2.cfm?pdf_num=1830

and this one, which i would put money on what is controlling the lightwave pocket-bright and the photon III...supposed to be really small (translate: pain-in-the-a$$ to solder)...

http://dbserv.maxim-ic.com/quick_view2.cfm?pdf_num=2166

anyone play around with these at all?...