The new board.

A project log for VederPSU

A tiny and efficient uC controlled lab power supply

riktwriktw 07/20/2016 at 21:340 Comments

The new board:

A few months ago I stumbled across this app note from Linear tech, describing how to build a lab power supply unit with their new LT3081 IC. This IC is very interesting for this application as it already has a current limiting function build in. It also has a temperature sensor build in and a way to monitor the current. This makes it near perfect for a lab power supply. The downsides are the price, the maximum output current and that a slight negative voltage is needed to really regulate to 0V.

Based on the older version of the VederPSU a new schematic was made, using the same DAC and ADC from the old VederPSU but with a different power stage based on the LT3081 app note. The reason for using the same ADC and DAC (the MAX11613 and MAX5802) is that these are one of the very few ADC's and DACs with an I2C interface and a separate voltage reference input. I want a single voltage reference for the whole system to make calibration easier and to be able to pick a voltage reference of choice.

The DAC has 2 outputs, one for the voltage and one for the current. With the current voltage reference they can go from 0 to 4.096V. The voltage output is multiplied by 10 using an opamp to create a 0-40V signal to control the output voltage with. The 0-4.096V for the current is converted to 0-200uA using an opamp. This combined with a current mirror controls the current limit of the LT3081's.

The ADC has 4 inputs, from which one is used as a voltage reference input. The 3 left are used to measure the output voltage, the output current and the temperature of the LT3081's.

The schematics can be found on the project page for anyone who wants to take a look.