Simple led circuits

[Trent]

Does anyone know where I can find schmatics on simple LED circuits online. For instance, Im wanting to try to run two or three 9200 mcd leds off one AAA at full brightness. Can't seem to find much info on how it do this.
Any help would be great. /ubbthreads/images/graemlins/confused.gif
Thanks Trent

 

[IlluminatingBikr]

The AAA will only give you around 1.5 volts, and the LEDs need about 3.6 or so. This gives you two options...
1.) Buy a voltage step-up converter
2.) Use two or three cells, rather than just one

I would recommend you try option number two, unless you need the circuit to be small, in which case a voltage step-up converter would be necessary.

Because you do not have a lot of voltage, you should wire the LEDs in parallel. This way they use more current (amperage), rather than voltage.

When using two cells you can direct drive the LEDs, or use some resistorance. When using three cells I would definitely recommend you add some resistance to the circuit. For more information about resistance, and how much you need, take a look here.

So basically your circuit is going to look something like this.

Image from here.

 

[Doug Owen]

You might want to start with this thread:

SatCure circuit

A couple of links there to just what you're looking for.

Be advised that efficiency of such schemes is generally low.

Doug Owen

 

[Doug Owen]

[ QUOTE ]
IlluminatingBikr said:
So basically your circuit is going to look something like this.

Image from here.

[/ QUOTE ]

Cool. Real (Conventional) current flow postive to negative (not that 'negative to positive electron flow' BS). How refreshing to see!

Doug Owen

 

[IlluminatingBikr]

Doug,

Interesting you say that. I have actually heard that the flow of electricy goes from negative to positive. It even says this in my basic electricity book.

I guess for our purposes though, with simple circuits (battery, LED/incandescent, and resistor) it doesn't really matter which way the electricty flows.

 

[UK Owl]

For all circuits think of the current as flowing from the + to the negative.

What actually happens (some of the early electricity pioneers got this wrong, hence the confusion and assumption of flow from + to -)is the electrons 'flow' from the - to the +.

You will only ever need to consider this when you are looking into the theory of semiconductors (transistors / diodes etc...) when doing a degree (or similar) in electronics.

As for powering three LED's from a single battery...

This can be done usng a variety of different dc-dc convertor chips.

for example you could use a MAX756 or MAX757 dc-dc convertor chip, both of these operate from only 0.7 volts (your battery will have approx 1.5 when new and this will lower with use), but either will only give a maximum of 5 volts output, thus you will need to use the LED's in parallel. Other DC-DC IC's are available, but many require at least 2 volts to operate.

Running a dc-dc convertor from a single cell will be VERY inefficient, so additional cells are desirable.

Note : If you use LED's in parallel you must bear in mind that they may each have a slightly different Vf, this may cause one LED to fail earlier than the others, and next thing you know you could end up with three destroyed LED's.

You need to use a separate resistor for each LED, and not parallel the LED's and use a single resistor as in the circuit provided by IlluminatingBikr.

 

[IlluminatingBikr]

[ QUOTE ]
UK Owl said:
You need to use a separate resistor for each LED, and not parallel the LED's and use a single resistor as in the circuit provided by IlluminatingBikr.

[/ QUOTE ]

UK Owl,

I have run 2 LEDs with one resistor for both of them, and it works fine. I have had that light for some time, and use it quite often.

I am aware of the fact that it is much better for each LED to have its own resistor, and I recommend that Trent does so. I could not find a picture of this configuration, and I thought the picture that I posted would at least give a general idea of the circuit.

So, Trent, I do recommend that you use a resistor for each LED. I'm sorry for the confusion.

 

[lumitoid]

Thanks for all the info. I think I can get somewhere now.
Thanks again.
Let me go back and study this info,im sure I have another question..Trent

 

[LED_ASAP]

Resisting each LED separately is only crucial if you run the LED's close to or above their rated power. If it's well below their rated value, it's safe to run them in parallel with one resistor on the bus. If one LED has a lower Vf, it will work harder, but as long as it doesn't fall into negative resistance region from a thermo-runaway, it will be OK.

 

[jeff1500]

Here are some that I've collected from CPF.

 

[Trent]

Has anyone dissected a arc aaa or a ultra to see what type of circuit they use /ubbthreads/images/graemlins/naughty.gif /ubbthreads/images/graemlins/naughty.gif

 

[Trent]

Has anyone dissected an arc aaa or Infinity ultra and figured out what kind of circuit they have.

 

[php_44]

The infinity Ultra has a circuit based on the LED drivers from Zetex ZXSC300/310/400 Single/Multi-cell LED Driver . Recently someone took one apart - search to find the link. It's encapsulated in epoxy so the teardown was not easy for the poster.

The non-ultra (40 hour) infinity light has a simple transistor and inductor based circuit, as does the ARC AAA. There are many such circuits in some recent links.

 

[NightStorm]

php_44,

The forum member's handle is nukiez and the links to his Luxi creation are here and here .

Dan

Oh, by the way.....I've disassembled a standard Infinity and it seems to have the same circuit. Production change or a factory goof? /ubbthreads/images/graemlins/confused.gif

 

[koala]

Thank you Dan for linking the Luxi post.
I find Jeff1500 website very informative for any one who want's to start building a LED circuit.

About the Infinity, I believe the earlier ones were equiped with a single transistor boost circuit then the later ones were upgraded to the ones used in Ultra.

Vince.

 

[Steelwolf]

[ QUOTE ]
nukiez said:

About the Infinity, I believe the earlier ones were equiped with a single transistor boost circuit then the later ones were upgraded to the ones used in Ultra.

Vince.

[/ QUOTE ]

So really, in a standard Infinity is an Ultra just waiting to bust out? (And in an Ultra is a Zetex circuit yearning for a LS LED?)

 

[koala]

I've only taken apart Ultras, so I am not in the position to answer this question. The assumption of an Infinity having the same circuit as an Ultra is taken from Dan's observation of his previous post above.

However it makes sense to have one type of circuit rather than two circuits that differs alot to cut down production cost.

Vince.

[ QUOTE ]
Steelwolf said:
So really, in a standard Infinity is an Ultra just waiting to bust out? (And in an Ultra is a Zetex circuit yearning for a LS LED?)

[/ QUOTE ]

 

[NightStorm]

Ok,

I just did a quick test and this circuit behaves identically to the description that nukiez gave in the second Luxi thread (260ma with a 3v lithium battery). Looks like the standard Infinity is an Ultra in sheeps clothing. /ubbthreads/images/graemlins/cool.gif

nukiez,

Do you have any specifications on the wire you used to replace to the sense resistor? The link that you provided in your Luxi thread has been dead for a while now. Thanks.

Dan

 

[INRETECH]

When designing your circuits, remember that LEDs are current devices, and will change their "resistance" with voltage

Using Ohms law will get you "close", but its always a very good idea to actually MEASURE the current of the LED (or circuit and divide) to make sure you are running the LEDs at the correct current

Although overdriving LEDs seems to be a favorite passion with a lot of companies, it does exceed the reccomendations by the company and will shorten the life of the LED

If you need more Light out of your circuit, add more LEDs - or change to a different type of LED

Blade Runner:

"The light that burns twice as bright - burns half as long"
"I make friends easily"

 

[koala]

Dan,
The first two pics appear to be dead but the rest area ok. I removed them from the misc dir. The wire strand was sourced from my junk yard so no spec on it. You can use anything, seriously. Start long, trim it slowly. I should stop here, anymore I will be hijacking. You can PM me.

Vince.