A linear MOSFET regulator for improving performance of the booster ramping power supplies at the APS

The APS booster ring uses ramping power supplies to power the sextupole, quadrupole, and dipole magnets as the beam energy ramps up linearly to 7 GeV. Due to the circuit topology used, those supplies are unable to follow the linear ramp to the desired accuracy. The best regulation achieved is 0.25% while 0.1% is desired. In addition to the unsatisfying regulation, those supplies are sensitive to AC line perturbation and are not able to reject AC line noises of more than a few tens of hertz. To improve the performance, a linear MOSFET regulation system using paralleled MOSFET devices in series with the power supply is proposed. The system uses a realtime current feedback loop to force the MOSFETs to work in the linear operation mode. By using this linear MOSFET regulator, the voltage drop on MOSFETs, and hence the voltage imposed on magnets, can be regulated very quickly. As a result, the regulation of the magnet current can be improved significantly. So far the simulation results show that with the linear regulator, the current regulation can be improved to better than 0.1%. Because of the high bandwidth of the linear regulator, it can reduce the harmonic content in the output current as well as reject the AC line disturbance. This paper discusses the circuit topology, the regulation method, and the simulation results.