PWM dimming circuit for LEDs in a buck converter

[nenya]

Hello all,
I am trying to build a circuit to perform PWM dimming of LEDs in a buck converter. To be honest, I have only been able to find resources such as datasheets for readily available ICs to perform this operation. But I would like to carry out the dimming using a microcontroller and without any off-the-shelf ICs. Any help in terms of reading material or sample circuits or advice will be much appreciated. I'm trying to build the entire circuit from scratch and also learn microcontroller programming. Since I'm a newbie, please let me know how I should approach this design problem (just the dimming circuit). Thanks in advance.

 

[barry]

I'm not sure what the connection between a buck converter and a PWM LED dimmer are. A buck converter is used as a voltage regulator. What do you mean by "LEDs in a buck converter"?
Regardless, it's a pretty simple task to control the brightness of an LED with PWM. You could use the built-in PWM controller found in many microprocessors, or you could make your own in software. Basically, all you have to do is generate a pulse train and vary the on-time of the pulse according to your desired brightness.

 

[nenya]

Hi Barry,
Thank you for your reply. I'm new to this kind of design and control so please bear with my questions, should they sound too simplistic and obvious. Appreciate all the help I'm getting here.
My question is basically related to factors like the necessity of a separate dimming switch with an LED string (I want to have 6 LED's in series in a string and eight such parallel strings), and the kind of control needed for the buck converter. I have looked online for resources but mostly I see 555 timers and ready-to-use off-the-shelf ICs to perform the dimming and control. I understand that in PWM dimming, the peak of the LED current stays constant while the duty varies, thus altering the average value of current flowing through the LED. Does this imply that I can only use a peak current controlled buck converter? Will a converter with an outer voltage and inner current loop present a viable solution or should it just be a current controlled converter?
Appreciate your time.

 

[barry]

You don't need a buck converter, or ANY kind of converter. As I said, you just need a variable pulse width signal which you would use to drive a mosfet. And what do you mean by "dimming and control". Dimming I understand but "control" of what? If this is a stand-alone circuit, i.e., no microprocessor, you can just use a 555 and mosfet.