Hello All,

I am planing to make a emergency lamp with 10 -12 white LEDs (Vf=3.2, I= 20mA) using 4 NiMH batteries (2100mAH) connected in series. Using a 555 chip in the boost mode I was able to drive the LEDs. However, since the circuit does not control the current the brightness goes down as the battery voltage drops.

Does someone know some commercial chips which can drive 10 -12 LEDs at constant current in the voltage range from 1.2 V to 4.8 V?

Thanks a lot in advance.

Gopal.

 

NiMH is problem I think.

Since u will be charging the battery during none emergency periods, I suggest to go for a Maintenance free Lead Acid Battery.

It will last longer and can handle more light time.
Further more u should PWM the Led's. it will increase efficiency.

By the way, how is the creative amp?

 

Thanks Riffa. I already tried to make a fast charger based on Maxim chip like the one I sent you last time. Lead acid would be bulkier and I would have to design a new circuit. Even with the lead acid battery I would still need a chip to drive the LED at constant current right?

The amplifier is working great. Thanks a lot for your efforts.

 

Hey, I was wondering abt those chips.
care to post the schema of the fast charger.
I got to make one for li-on's

Making constant current Led driver is quite easy.
I bet u can make one using LM317.

Check them pages. Some more info

 

This pdf has all the info you need for the chips I sent

http://pdfserv.maximintegrated.com/en/ds/1666.pdf

Have fun !!!

 

PWM does not make LEDs more efficient. PWM dims the LEDs so they do not use as much power as when they are brighter.

 

You might want to try something like this:

http://dx.com/p/mr16-4w-4-led-6500k...0208?rt=1&p=1&m=1&r=3&k=1&t=1&s=30825&u=30208

There are all kinds of configurations. They have their own current regulation.

I have not tried them myself but I have some on order.

 

Here's an idea to use with the NIMH batteries.
Does need only a small serial MCU.
The 6969 supports 16 LED's
http://www.maximintegrated.com/data...imintegrated.com/en/results.mvp?fam=disp_driv

 

Thanks spinnaker and tubeguy.

I am actually trying to charge 4 NiMH batteries using max712 which I would use to power the LEDs. I would like to have some chip that would be capable of driving 10-12 LEDs at constant current (between 1.2 to 4.8V).

Microcontroller is not a option for me since they would need additional power source.

 

Crap ! I missed your point.

To make a 32V Led river from 4 Nimh. you will need a boost converter.
I donno any thing that is readily available.

But lessee what I can dig up!

 

Check it out !

 

Thanks a lot Rifaa.

 

Hello Riffa,

I decided to use 555 to drive 20 white LEDS series. I live in place where there are no good electronic spare shops and it would take 2 - 3 weeks if I try to order some LED driver chips through internet.

some comments regarding the attached circuit

J1 is for power supply (12 V , 2A)
JP1- to be connected if 4 NiCd/NiMH are charged. leave it open if 2 cells are used
J2 is to connect batteries in series
JP2 - is to connect external switch to drive the 555 chip
J3- for connecting LEDs in series

I will try to solder components on the board tomorrow if I manage to find some time.

 

Hello Riffa,

I decided to use 555 to drive 20 white LEDS series. I live in place where there are no good electronic spare shops and it would take 2 - 3 weeks if I try to order some LED driver chips through internet.

some comments regarding the attached circuit

J1 is for power supply (12 V , 2A)
JP1- to be connected if 4 NiCd/NiMH are charged. leave it open if 2 cells are used
J2 is to connect batteries in series
JP2 - is to connect external switch to drive the 555 chip
J3- for connecting LEDs in series

I will try to solder components on the board tomorrow if I manage to find some time.

Lesse if the boost works.