Home brew SMPS

[Thunderchild]

Well the saga continues..... (formerly known as inductorless SMPS)

I've brought my design up to scratch a bit and have managed to factor in a real world MOSFET. the only thing I can't understand is why increasing the capacitor size increases the tendency to oscillate a bit.

If I understood correctly the operating frequency should be higher than the LC resonant frequency, how do I acheive this ? I'm begining to think that its the LC resonant frequenct that to some extent is controlling the frequency that the circuit works at.

Reducing the load resistance actually descreases frequency although i assumed the oposite as surely the circuit has to work faster to supply more current.

again this is a theoretical model so feal free to bash it with real life expectations

 

[picbits]

Just pop round mine and I'll sort you out a LT1074CT7 and 100uH 7A inductor for a fiver

Much easier than trying to design your own and get the switching frequencies right

 

[Sceadwian]

If this is an inductorless supply, then why are there three inductors in that circuit? What kind of monitor are you using anyways, that screen capture was extremely wide!

 

[Thunderchild]

If this is an inductorless supply, then why are there three inductors in that circuit? What kind of monitor are you using anyways, that screen capture was extremely wide!

No this is not inductorless its supposed to be a proper SMPS (well as close as a bumbling amateur like me can get) my previous idea was without an inductor but I got over that after some very intelligent and informative discussion in my previous thread.

my screen ? ah yes nice isn't it ? lets me see modern films in true wide-screen. I had it custom built from a couple of smaller screens, had the 2 smaller panels mounted in a a single frame and a special controller made.... Just kidding, I have 2 monitors 1440 X 900 and 1024 X 768, when you do a screen capture it captures both, I find using 2 handy as you can see I can have the circuit on one and the oscilloscope on the other, also very handy for photo editing.

 

[Sceadwian]

Thunderchild, have you taken a look at Wikipedia's entry on buck/boost and sepic converter topologies?