Hello.
This has been standing still for some time and now I have done as previously advices, which is to re-design the power supply and base it on a SMPS(Switch-Mode Power Supply) with post-regulation by linear regulator.
I did not want to go that way when I first got that view but I knew that it was the way to go since a linear power supply wastes a lot of power and efficiency, from the start I did not want to even think about SMPS at all with the understanding that a SMPS would bring lots and lots of more noise at the final output. But since then I have read that if designed properly there should be no noticeable difference between a linear/switch-mode power supply?
I know in principle how the work but I have just begun learning about buck-converters and I have a couple of thoughts that I need some guidance with.
I started looking through Linear Technology's(linear.com) switch mode regulators and I found that there are quite a few that can output as much as 60V, but many more that can go to 36V which will suffice. But some have a max output current of ex, 20mA or 100mA and others a max output current of tens of Amps. What kind of applications does these very different power levels tend to?
In my last design I had a linear regulator who's output was driving a NPN darlington transistor in part to increase the output current but that also gave the opportunity to without any great pain apply quite aggressive filtering at the regulator input since so very little current are going through there. I have never built the complete circuit and I have no measurements to share or discuss about that but I'm not totally wrong it seemed lie a good idea.
But now its a new story where that will not be suitable, I think not at least.
As I see it now this is what I need to find out about:
How to treat the noise from a SMPS, where to apply what kind of filter/filters.
How to tie together the DAC controlled Feedback resistor divider with the switch-mode step-down converter and to have it also controlling the post-regulation regulator...
I need to find a suitable SMPS regulator, I see there are some with very complex external support circuits while some has next to no external circuits. I need a simple one and I need to check what kind of technique is used to adjust the output voltage, I hope I can still use the excellent low voltage DAC circuit that Klaus provided
If anyone have something to add to this please do, in any case I will post again when I have made any progress.
About the previous post, I have been going for two reference IC's before not because any real board constraints as such but the layout proved to make it a problem with only one. The DAC and the ADC is used in very different places in the circuit and it was very difficult and it mead a mess when trying to do it as you suggests. Difficult to to level that I was happy to pay for one more reference circuit.
Thanks for all responses, really appreciate it.
Regards