Help With Power Supply Design

[BitShard]

Hi all,

This is my first electronics design project in a few years, and first design of something on this scale. Basically, this is a power supply which I'm trying to design based off of Dave's uSupply, minus a few features, and add a few features, to tailor it more towards my requirements.

What I think I'll do differently: Doesn't need to be so small, doesn't need to be battery powered, dual rail, doesn't need ultra low current sense

So far I've only completed preliminary requirements, bill of materials, and system diagram. Would you be able to point out any flaws, incompatibilities, or improvements?

Thanks! 

Requirements:
Functional:
-Soft latching power button
-Lock output switch (prevents output voltage/current limit from changing)
-Rotary Encoders for voltage/current adjust
-Output enabled/stable LED per rail
-Load switches
Non-Functional:
-Dual Rail
-0-20v output per rail
-0-1A output per rail
-Current Limit
-Low Noise
-Reasonable efficiency (using tracking pre-regulator)
-Single supply input
-Software controlled (Micro)
-Voltage sensing

Bill of Materials:
-Regulator: LT3080
-Op Amps: LM358
-Constant Current: LM334
-DAC: MCP4716
-Voltage Reference: ISL21070
-High Side Current Sense: INA219
DC-DC: MIC2253
EPOT: MCP4017T
Display: EA DOGM204W-A (subject to change, 7seg or smaller etc)
ADC: ADC101C021CIMK

System Diagram attached

[Strada916]

LT3080 has a bug where it stops working in some circumstances. Search LT3080 in this forum.

[blackdog]

Hi BitShard,

Do not make biginners mistake's en put al your energy in designing the digital part! ;-)

1e
Design the analog part, make sure its works OK, test it dynamic, you need a scoop, pulsgenerator enz.

2e
DC-DC converters are difficult and they push high frequenties in your analog circuits, it is difficult to screen them.

3e
A low noise PSU with DC-DC converters(high power), is extreemly difficult.

4e
NO, CPU in the voltage or controle loop!

5e
Use "real" opamps, not lm324
Take a look at ADA4077 series.

6e
Make shure that you know what "Phase Margin" is, extreemly important to keep your design stable.
If you insert an current sense IC, you make the phase margin worse, thats normal, but keep in mind when designing of the analog part.
If you ignore it, the circuit will certainly generate when the current limit kicks in.

Just 2 cent...

Kind regarts,
Blackdog

[BitShard]

Thanks for your replies, I'll go check out the LT3080 bug.

I'm fairly proficient with digital design (in terms of software and software/hardware interface) so I don't think that should be too much of a problem. The analog part is pretty much straight from Dave's uSupply, so it should work fairly well, though I would breadboard and test it, except I am currently lacking any lab equipment at all, so I'm trying to design it before I set up my lab

DC - DC converters would also help to avoid setting the thing on fire when it's dissipating 20W through the LT3080

It shouldn't be too bad if I include a RC filter and possibly RF bead. It doesn't need to be ultra low noise, but it would be preferable to keep it as low noise as possible.

The voltage control loop is governed by the voltage applied through the DAC into the set pin of the LT 3080

Swapping the Op Amps shouldn't be that hard, I just chose those ones because Dave did.
I'll go check those other out.

I have no idea what that is. I'll ask my electronics professor to explain it to me on monday.

Thanks for the feedback