High Dynamic Range Precision Current Supply

To evaluate the performance of this device, I started with connecting it up to a MetaShunt V2, without prior calibration of anything except the highest 2 current shunts of MetaShunt V2.

The table below compares the expected current (from the design), compared to measurements from MetaShunt V2. The images below also show these results. Overall, the expected and measured current matches very well, all within 1% or better. Future testing will show the reliability of the current supply as a reference truth.

This project is fairly straightforward. The constant current supply circuit is based off of the Analog Devices AN-1530 application note for a low cost, precision constant current supply. The AD8276 Difference Amplifier and the AD8603 Op Amp are used in the current supply circuit. However, to achieve a high dynamic range, 8 different MOSFET controlled shunt resistors are used for setting the current, and the reference voltage is provided either by a fixed high 0.2% accuracy precision voltage reference or by a precision DAC (TI DAC80501). With this design then, there are two operational modes:

1. High precision, constant reference voltage mode
2. Precision, adjustable reference voltage mode

The MOSFETs and DAC are controlled by an onboard STM32L4 microcontroller, with USB and power isolated so that this device can get power from and communicate with a computer over a USB-C cable, while remaining electrically isolated.