Howland Current Source Applied to Magnetic Field Generation in a Tri-Axial Helmholtz Coil

This work describes the design and testing of a power Voltage-Controlled Current Source (VCCS) based on the Howland Current Source (HCS) topology. This source is part of a system that contains a three-axial Helmholtz coil and is used to generate a controlled magnetic field environment for aerospace applications. Initially, the paper presents the HCS theory and practical limitations on the premise that the system must be built using low-cost off-the-shelf components. The paper also carefully address on how to design and plan the VCCS matching physical and electrical parameters/limitations of a specific Helmholtz coil. All project details as well as the built VCCS electronics and its results are shown. These include linearity and a first order calibration test, stability and low-frequency error measurement, step response and a frequency limitation analysis. The built source is capable of sourcing up to ±1.5 A at ±25 V, maintaining its linearity and achieving an error smaller than 0.5% with a first order calibration. The final HCS prototype together with the Helmholtz coil allows an excellent capability regarding magnetic field generation for both open and closed-loop applications.