A high-power LED torch using a single AA-battery

Step 7 What's next?

I hope you have lots of fun making these lights.

Here are a couple of different combinations: 4-LEDs or 1 120mA LED. The single LED is simple enough that I soldered the components directly onto the leads of the LED. Sealed in 3/4" heat-shrink tubing.

You will find much more about LED circuits at my Website: http://www.quantsuff.com Give me a visit and let me know what you are building this week!

Comments

[Rusdy]

I wonder how efficient this circuit is (i.e. volts and current input and output)

[qs]

With a new alkaline at 1.6v, it's 78% efficient, but drops to about 65% with a 1.2v Nicad - it has to do with the Vce drop across the transistors at 200mA.

[Rusdy]

I was a wee bit pessimistic when I saw the circuit. But after testing it myself in PSPICE, I stand corrected. It is pretty damn efficient for such a simple blocking oscillator circuit (as they're not really efficient). Those components choice, do give efficient conversion. At 1.2 V, PSPICE simulation does give around 40-50% efficient, and it's consistent down to 1V. The transistor does play a big factor here though (as you commented), definitely need high gain in high frequency, your typical hobbyst transistor (such as BC547/557) won't give the same efficiency (and less brightness as well for the LED). I wish I saw your circuit first, before I ventured out to LM2623 from National Semiconductor. It definitely gives 70-80% efficiency down to 0.9V. Unfortunately, it only comes in a surface mount (for a very good reason, with upto 2MHz switching frequency), so it's pretty expensive to work with.

[qs]

I've been experimenting with the flyback circuit since the first Joule Thieves went around the web. You can see my efforts here on my website.

Normally I use low Vce transistors like the 2SD965 which really helps in the efficiency, but, in designing this circuit here, I wanted one that can be duplicated by the average hobbyist without access to the fancier equipment and components.

I'm glad you like it.

[Sagar Gondaliya]

your ideas are amazing. i was just wondering, i dont have a very good monitor so i cant read your schematics on the webite. could you maybe post some computer generated ones so i could read them? thnx very much in advance -a fellow maker

[qs]

Tell me the ones you are having trouble with and I can try and send you better images.

Also, some of the circuits on my website link to larger ones too.

[Sagar Gondaliya]

im mainly having problems with the hack-lite one. thnx

[qs]

Here's a bigger image. Or you can try this link which is accessible from the smaller pic on my website as well.

Let me know if this is helpful.

[Sagar Gondaliya]

yea it is. thnx

[carpeteknus]

Excelent ! lined up for my next weekend project :) Do you know how long will a new alkaline battery last? my rough math says around 20 hours for a 2000mA h(2000mAh/(4x25mA) ), but i'm not sure that's the complete discharge calculation

[sign-up]

Remember that the LEDs are run at 3.3v, while the battery is only 1.5v

Using the power calculation:
Input = 2500mAH * 1.5v = 3,750mWH
Output = 4 * 3.3v * 25ma = 330mW

So, to get operation hours: Input / Output = 11.4 hours. Of course there is also a penalty in the conversion (in-)efficiency we have to factor in, about 75% by my observations, which lowers the operation time to about 8-1/2 hr.