I would like to design 1W LED array having least 9 LEDs which uses 12v 5amp bike battery so i can rely on during power failures. i have tried a circuit which include four stages each including three LED and a 50Ω resistor in series.
but unable to lumin to required extent. please help me.. thank you

 

Use a 10W LED.

 

10w LED not available here in my place. thats why I clearly specified availability in my thread.

 

Hello,

I've look for several Datas of 1W - Leds. I found that the Vf = 3,5V and If = 350mA.

If you put 3 LEDs in series you have Vf = 10,5V and If = 350mA. To use this LEDs at 12V you need a resistor of 4,2 Ohms. 50 Ohms is too much.

Regards

Rainer


PS: Sorry, if my English is not so good.

 

but practically resistance below 50 ohms causing heating up of LEDs. also the LED on cathode side of the battery suffers with max voltage drop rather than dividing equally!

 

Not sure if driving 350mA LEDs at 30mA is really the solution here.

I've never worked with high power LEDs before but imagine you'd need to have some sort of constant current device rather than rely on a resistor in series with a number of LEDs.

 

Hello,

high - power LEDs need heatsinks.

Please look for this Datasheet an application-notes.

http://www.avagotech.com/docs/AV02-1640EN

http://www.avagotech.com/docs/AV02-1958EN


Regards

Rainer

 

hi all, my first post.

theres constant current/constant voltage driver bits on ebay ranging from 1.99 upwards.. 3 350mah 3.2-3.5v diode type led's work quite well at 8-9 volts @50mah.(serries).

no where near 'on full' but light a room well enough with no lenses or heat sinks, i could touch them after 5 minutes without burns, although reading would have to be fairly close up to the light sourse.

a better solusion is the car reversing LEDs, small black round case with lens, waterproof units, 2 for £3.00 dilivered, put two to a jack plug, you can read off of those no problems, reflect them off of the ceiling or theyre blairingly bright.(i havent played with them, pulsed or series etc as yet.(9 amp li-ion batteries for 4 hours with two lights they still lit very well).

 

I found LM317 also a best choice but it can drive a current maximum of 1.5A.
And i would like to design my own rather than buying it, so i can improve my knowledge too...,

 

Hello,

Have a look at this post made by Bill_Marsden on current limiting for the leds:
http://forum.allaboutcircuits.com/showpost.php?p=117638&postcount=3

The 1 Watt leds need to me cooled with a heatsink.
If they get to hot the lifetime will be very short.

Bertus

 

thank you bertus.

as your suggestion i had gone through bill marsden's article but in every case the current through LED is not more than 50mA but here i'm trying with 350mA LED so it can produce greater lumen.
I expect each LED should at least be operated with 200mA which is not possible by any series combination i felt....,

 

Hello,

I was revering to left and middle schematics of fig. 2.4 on that page.

Now the current limiting resistors (R2 and R3) are 30 Ohms, leading to a current of about 0.7 / 30 = 23 mA.
Lowing those resistors to 3.3 Ohms and using more powerfull transistors, the current will be about 0.7 / 3.3 = 212 mA.

All leds and transistors need to be cooled.

Bertus

 

ok. and which pnp transistor you suggest here?

 

Hello,

You could use one of the following:

Type               Pol             Pkg              Vceo           Ic            Hfe             fT(Hz)         Pwr(W)  
2N4388             PNP             TO66             60             2             25-100           25M             20 
2N5597             PNP             TO66             60             2             70-200           60M             20  
2N5600             PNP             TO66             80             2             30-90            50M             20 
2N5601             PNP             TO66             80             2             70-200           50M             20  
2N5603             PNP             TO66             100            2             30-90            50M             20

Bertus

 

Any equivalent for 1N4454?

 

Hello,

Almost any diode can be used there, like the 1N4000 series or 1N5400 series.

Bertus

 

Use LM2576. Its Switching regulator , no heating and efficiency is more.It can drive upto 3A. Connect all LED's in parallel and the buck circuit will convert 12V to fixed 3.3V.Also other voltage levels if you plan to connect in series.

OR if you use LM317 then go with 4A switching regulator circuit given in datasheet of LM317(national semiconductors) page 19. Also LM138 and LM150 have upto 5A.

 

Use LM2576. Its Switching regulator , no heating and efficiency is more.It can drive upto 3A. Connect all LED's in parallel and the buck circuit will convert 12V to fixed 3.3V.Also other voltage levels if you plan to connect in series.

OR if you use LM317 then go with 4A switching regulator circuit given in datasheet of LM317(national semiconductors) page 19. Also LM138 and LM150 have upto 5A.

I would use the adjustable version, and maybe use a little less than 3.3V

But not good to use as dimmer, easy to go higher than 3V...