Hello friends,
I want to build a simple DC-DC converter to drive 15 LEDs from a 3V source.
(I know there exist a similar topic on that here, employing 555, but actually I have trouble calculating the inductor.)
The idea is to use a PWM to drive a low power NPN transistor. The transistor will switch on and off a coil which will ensure the necessary current for the LEDs (see the figure).
Please, help me to calculate the inductor L!!! I am a bit frustrated because I don't know how L depends on the PWM frequency and how L depends on load (15 LEDs x 2,4V drop = 36V!). How to calculate L such that the current is constant - say 10mA.
The only formula I know about L is:
L = μ0 . μfe . (S / lav) . ω^2
where S is the area, lav is the average magnetic line and w is the number of turns. Nothing about I and the frequency...
What will happen if I try to control the PWM duty cycle? I want to be able to dim the LEDs.
Thank you
I want to build a simple DC-DC converter to drive 15 LEDs from a 3V source.
(I know there exist a similar topic on that here, employing 555, but actually I have trouble calculating the inductor.)
The idea is to use a PWM to drive a low power NPN transistor. The transistor will switch on and off a coil which will ensure the necessary current for the LEDs (see the figure).
Please, help me to calculate the inductor L!!! I am a bit frustrated because I don't know how L depends on the PWM frequency and how L depends on load (15 LEDs x 2,4V drop = 36V!). How to calculate L such that the current is constant - say 10mA.
The only formula I know about L is:
L = μ0 . μfe . (S / lav) . ω^2
where S is the area, lav is the average magnetic line and w is the number of turns. Nothing about I and the frequency...
What will happen if I try to control the PWM duty cycle? I want to be able to dim the LEDs.
Thank you