Feedback on PSU design

[Mephitus]

I created this build using the LT3081 as the foundation. The LT3082LT3092 providing a small current source to offset the set pin, allowing use of a 10K pot that I already have in my bin. Much of the design takes points from the DC2132 demo board and from datasheet examples. Been working on it for over a month now. So I hope that my efforts are not completely incompetent as this is my very first wack at building anything more than a educational/example circuit.

My goal was a 24V 3A supply with as small a footprint as possible. The SMD component footprints are all generic 0805, I can resize/nudge things around to accoomodate bigger/smaller sizes.
The spice model seems to test out just fine and it is attached below. I just modified the one provided for the DC2132. If there are any gross errors or major problems with my design or layout, please let me know.

[dom0]

24V 3A

LT3081 datasheet figure "3081 G12".

[Mephitus]

LT3081 datasheet figure "3081 G12".

The datasheet for the DC2132 shows an output of 3amps at 24v load. Did I missread the diagram, or are they using the LT8612 as a current source?
The spice model linear supplied shows the full range too, is the model incorrect? Oh well, I can accept 18V 2.4A with as tiny as this thing is.

[prasimix]

How are you going to cool these tiny thing? Even with fan some additional cooper could help a lot. Also with two layers lots of vias to the other side can help to make connection with external heatsink (of course with silicone rubber or some other way of isolation if required.)
Also what's about pre-regulation if output voltage will be adjustable?

[T3sl4co1l]

What's with your layout?  It looks like balls...at least, Altium(?) seems to think so with the DRCs...?!?!  I don't see the pinouts and routing matching up either...

Tim

[Mephitus]

How are you going to cool these tiny thing? Even with fan some additional cooper could help a lot. Also with two layers lots of vias to the other side can help to make connection with external heatsink (of course with silicone rubber or some other way of isolation if required.)
Also what's about pre-regulation if output voltage will be adjustable?

I was hoping to have it either on top of an old CPU cooler with a sil pad or an aluminum heatsink over the top of the 2 regulators. Hense why I put them parallel to each other. (maybe both) This is just my first pass at this layout and the very first one I have ever tried outside of a protoboard.

I did not really think of pre-regulation. Is there a good circuit guide you might recommend towards this? Or point me in the right direction for where I should be studying?

[Mephitus]

What's with your layout?  It looks like balls...at least, Altium(?) seems to think so with the DRCs...?!?!  I don't see the pinouts and routing matching up either...

Tim

I was using Altium 10. It's my very first attempt at a PCB layout and I was trying to keep it single sided routing with the 2nd layer entirely dedicated to ground. Mostly to see if I could do it at all.  I could take another swing at it allowing traces on a 2nd layer to clean things up a ton. Eventually I hoped to place an order from someone like dirtypcb's or such.

Sorry, I know its messy as hell and some of the parts/pins are swapped a bit. Think of this more as a first time trial to see how much I understand of the basic concepts and where I need to put more effort of study. I can post up a link for my source files if someone is willing to give me some more pointers?

[prasimix]

Sorry, I know its messy as hell and some of the parts/pins are swapped a bit. Think of this more as a first time trial to see how much I understand of the basic concepts and where I need to put more effort of study. I can post up a link for my source files if someone is willing to give me some more pointers?

For compact design you need switching pre-regulator. The DC2132 has one. I'm currently waiting for PCB to arrive of one that is presented here based on LTC3864. I found Interesting the following SMPS controllers: TPS54560, LM5576 and LT3724. All of them should deliver 3 A and accept pretty high input voltage.

[Mephitus]

For compact design you need switching pre-regulator. The DC2132 has one. I'm currently waiting for PCB to arrive of one that is presented here based on LTC3864. I found Interesting the following SMPS controllers: TPS54560, LM5576 and LT3724. All of them should deliver 3 A and accept pretty high input voltage.

Thanks for the link. I will take a careful look at that, at a glance it looks pretty awesome. Seems I should spend some more study time on the books I have to better understand a lot of these concepts.