Step-Up Voltage Circuits Please

(1) I want to convert my old 3 Volt bicycle lights to work with white LEDs.

(2) I want to convert old 1.5 Volt single cell torches to work with white LEDs

Obvious problem: batteries give 1.5 or 3 Volts, but white LEDs require about 3.3 Volts to achieve useful light output.


(3) I want to convert a 6 Volt hand lamp to operate with 12 Volt LED bulb assemblies.

Please can anyone give me moderately simple circuits to step up these battery voltages with good efficiency ? Or a link to some ?

Or is there (as I suspect there should be by now) a nice cheap little IC that will do these jobs for me ?

Thanks for any help you can give.

Hi!
Whatch this video from Dave of the EEVBlog: http://www.youtube.com/watch?v=qGp82xhybs4
I find this a very good tutorial on designing DC-DC converters like you need. It will tell you exactly what to do and what not to do and it works with an IC!
Regards,
Boi

What you need is a switching constant current source (It's better to drive LEDs with a current source rather than a voltage source).

For cases where the source voltage is 1.6V to 18V, there is the Linear LT1618 in constant current mode. The app notes on the Datasheet (http://cds.linear.com/docs/Datasheet/1618fas.pdf) show how to drive the LEDs.

For a 1.5V input, I don't know, but I'm sure it's possible. Try Googleing things like:

* "switching led driver IC with internal fet"
* "battery powered switching LED driver IC"
* "battery powered constant current boost IC"

I just discovered the LT1932 which might work for the 1.5V case, and even for the 3V case.

Also, for the 6V to 12V array case, the LT1618 can be used in the constant voltage mode, as long as the current requirements of the 12V array don't exceed it's capability.