Digital Precision Power Supply Project - Open Source DAC-to-ADC PMBus / I2C

[quantumvolt]

I have taken a long time interest in PMBus [http://pmbus.org/about.html]:

"The Power Management Bus (PMBus) is an open-standard digital power management protocol: simple, standard, flexible, extensible, and easy to program for. The PMBus command language enables communication between components of a power system: CPUs, power supplies, power converters, and more."

PMBus (which is based on I2C / SMBus) as a power supply management system enables you to:

  - configure, control, measure-monitor / report-stats and protect (from overload or other fault conditions) your power supplies / converters / regulators / voltage references

by continuously supervising:

  - input voltage, input current, output voltage, output current, die/device’s internal temperature (for compliant chips only), external temperature (and in some cases auxiliary voltage inputs) for multiple POLs (Point of Load - a remotely supervised switched or linear DC/DC converter/regulator or any AC/DC power supply with a Feedback or Trim input)


As it is a big task to explain my thoughts about this project, I have decided to just open a thread and post whenever I feel like it.

Below is two pictures of my "feasibility study" - a "hacked" demo board (DC1962) from Linear Technology. The board and the USB-to-I2C adapter were given free of charge from LTC. Thank you very much.

It is important though to say that PMBus is actively supported by and developed for by many of the big chip houses: LTC, TI, Intersil, ADI, Microchip, Maxim and more. There are parts to be bought and sampled, quite a few demo boards and many free GUI's. And there is the open PMBus spec, loads of good data sheets and app-notes, and a few lines of public C code waiting for those who want to start to use it.

The LTC PMBus controller board (hacked for a linear regulator - one of the 14 switch-mode supplies on the board is removed and replaced by a linear series regulator), and the free LTpowerPlay GUI. The action photographed is setting CH7 - a 1 Volt nominal output - from 0.75 to 0.74 Volt. The reaction of the linear series regulator to the DAC control signal is captured by the output voltage sense ADC and displayed in the monitor window (the low right part of screen).

[quantumvolt]

So - where do I want to go with this project? Well - after having seen some of the different more or less successful 'proprietary' attempts to make a digital bench supply on this and other forums, I decided that I want to go for the industry standard versatility of the PMBus. That leaves me with the option to run a ready-to-play demo board from the very beginning, and add more when I am in the mood and have time.

I have two projects:

- a Programmable Precision DC Source (2-16 Volt, 1 Amp 0.01 %, low noise) controlled by a 16 Bit DAC and with 24 Bit ADC feedback

- a Testbed for Voltage References with controllable/measurable line input voltage change stability, ripple/noise rejection, temperature coefficient, humidity change "reaction" and general logging of long time performance with RS232 (or GPIB, if you use it) interface to external precision instruments

All I need is a PC with a C compilator, an Arduino/PIC/any-uC, a toroid transformer, a battery pack (for noise critical applications - an old MC/car battery is fine), a good voltage reference (5-15 dollars), a 16 Bit DAC / 24 Bit ADC pair (I2C or SPI - less then 30 dollars in total), some scrap op amps/transistors/diodes/resistors/capacitors, a PMBus Controller (10 dollars or so and up) and a lot of time.