Frequency dependent impedance with steep roll-off

Thread Starter


Joined Apr 15, 2019
I have a DC motor, which is used as an electromagnetic brake. However I want to leave certain frequencies uninhibited, so I thought this should be possible by adding a highpass filter on the DC motor mains. The Idea is that if I high-pass the current through the shunt, that for a sinusoidal velocity input below 3 Hz no current flows through the motor coils resulting in no back-emf torque.

The circuit below consists of a sinusoidal voltage source as a result of the emf of the DC motor, the armature inductance (L1) and resistance(R1). C1 is just there to signify the shunt type behavior I want to achieve.

What I would like to achieve is a frequency response somewhat like the picture below. The important part is the relatively close proximity of pass (3Hz< fpass <10Hz) and stopband (<1Hz) frequencies.

I would like to know if it is possible to obtain such a filter on the total current and whether this could be done without any need for active control (aside from opamps)