  Magnetic Feshbach resonances are a key tool in the field of ultracold quantum
gases, but their full exploitation requires the generation of large, stable
magnetic fields up to 1000 G with fractional stabilities of better than
$10^{-4}$. Design considerations for electromagnets producing these fields,
such as optical access and fast dynamical response, mean that electric currents
in excess of 100 A are often needed to obtain the requisite field strengths. We
describe a simple digital proportional-integral-derivative current controller
constructed using a field-programmable gate array and off-the-shelf evaluation
boards which allows for gain scheduling, enabling optimal control of current
sources with non-linear actuators. Our controller can stabilize an electric
current of 337.5 A to the level of $7.5\times 10^{-7}$ in an averaging time of
10 minutes and with a control bandwidth of 2 kHz.
