Sorry for the long question, it's really opinions I seek which is why I felt I needed to explain the scenario and how much I know/don't know. I would really like some input on my design. I am designing a DC/DC SMPS(switch mode power supply) boost converter.
The general advice about DCM(discontinuous conduction mode) in SMPS boost converters is to try and avoid it. This advice is usually backed up by a barrage of equations. Unfortunately I am not very good at Engineering Maths, but if the DCM is anything like the equations, I get the point, I'll stay away :D ! Aside from adjusting switching frequency, increasing the inductance value looks the biggest way to avoid DCM. In my boost converter the output voltage can be varied(it's microcontroller based) and I expect the load to make the input current vary from 10mA(high inductance needed) to 4A(relatively high saturation current needed). I have had some problems in finding an inductor that would fit my specification, I used Digikeys' Parametric search.
Since inductance value is mostly inversely correlated to saturation current, I understand why it may be hard to find my golden inductor. I have found about 8 out of tens of thousands on Digikeys' site, but they are unshielded(which I don't want for this application), large :( and expensive :( .
I understand how DCM works well enough, that the converter enters DCM when the load current is so low that the discharge cycle of the inductor lets the inductor current slip past zero.
So here is my take, since this application is microcontroller based, couldn't one simply just stop the discharge of the inductor when the current nears zero? I know this means distorting the PWM. What I am suggesting is having two microcontroller pins connected to the base of the MOSFET(or gate driver to MOSFET) that controls the inductor charging. One is switched based on the PWM while another simply goes high when inductor current value drops to the microamperes range. I plan to use another MOSFET (Q2) in the inductor discharge path to measure the inductor current. I'll be using the Vds of the MOSFET (Q2) to calculate the inductor current and decide when step in to charge the inductor. So do I get the IEEE prize for SMPS design :D ? Well I doubt it, as while I was learning how to design a boost converter(which I did off the internet thanks to so many kind people), most of the designs I saw used a SMPS controller so I can understand that there wouldn't have been as much flexibility as with a microcontroller based approach because I never saw anyone discuss this.
So my question is, what are your thoughts? I haven't had the opportunity to test it on a breadboard yet, will do soon, but whether it works or not, I want to know if there is something I am missing, or the opinions of anyone on this idea. I am not an experienced circuit designer so I could do with some input.
Thanks for taking the time to read the question. :)