A High-Current Low-Pass Filter for Magnet Power Supplies

The majority of high-current dc power supplies for beam bending magnets have well known LCR low-pass ripple filters. To avoid prohibitive heat losses, the filter damping resistor is in series with the capacitor and not in the dc path. Such filters, when critically damped, attenuate high frequencies by 6 dB/octave. This paper analyzes an improved underdamped LCR filter which attenuates high frequencies by 12 dB/octave. Depending on the application, the improved filter can be designed to have an oscillatory or a non-oscillatory response to a step change of the input voltage. Design curves are given which show the frequency response and the time response to a unit step of a normalized improved filter for various degrees of damping.