I'm working on a small project which involves an ATtiny controlling 4 LEDs. Luckily, 3/4 are colors that can run with Vf <2.5V but the blue one is being a problem.

I'm considering the following options but I'm not sure which is the best to take:

1.) 3.3V to 5V boost regulator. At my quantities I should be able to get one for ~0.50. This solves the problem but I'm going to have to recklessly burn away the excess with more current limiting than I would running the outputs @ 3V for the other LEDs

2.) Charge Pump. The 555 Timer used for driving a blue LED in this manner in the workbook is excessively costly. I could build a discrete one but I'm worried that with only 2k of program memory left on my micro that I should save the resources. Also, ordering the parts almost makes the boost regulator worth it.

Any input?

Thanks.

 

Cheap solar garden lights use a transistor or two oscillator/rectifier to boost the 1.2V from a Ni-Cad cell to 3.5V to operate a white or blue LED all night.

 

Look at "Joule Theif" circuits. some are more efficient than others, but do boost from 0.6v to whatever is needed (blocking oscillator). They are NOT extremely efficient, but are very simple to build.

They are built with 1-3 transistors, you'd want a protection diode on the line powering the circuit, and it can't easily be dimmed with PWM (very low frequency PWM might work).

If you are running off a coin cell, it may not be the best route due to efficiency issues.

 

You can use the AVR pin as a booster output. All you need is a driving signal of some 10 kHz.