A 10-A High-Precision DC Current Source With Stability Better Than 0.1 ppm/h

The principle, design, and measurement of a 10-A highly stable dc current source is described. Based on a modified low-frequency equivalent model of the MOSFET, we obtain the strict current equation of the MOSFET-based voltage-controlled current source. Factors determining the current stability are investigated and reasonable selection criteria for the key components are discussed. Reasons for oscillation due to the high parasitic capacitance of the paralleled MOSFETs with low set of drain-source voltage are explained and a combined noise gain and lead compensation method is proposed. The best measurement results show that the relative standard deviation and relative drift of the current in 1 h are, respectively, 7.5×10^-8 and 2.2×10^-8. The current source has been used in our high current meter stability evaluation experiments and can be used for other cases with appropriate improvement, such as the Joule Balance Project to redefine the kilogram at National Institute of Metrology.