Electronics > Projects, Designs, and Technical Stuff
How to test a low-impedance filter circuit?
T3sl4co1l:
Yes, quite. The 50/50 ohm test is the general case, unless we know something more specific, which we do in this case. An AC current source at the load side would be a more correct model here.
Again, the input isn't doing much (2u rolls off with 50 ohms at >>10kHz), but if you don't mind the use of more inductors, that Q doesn't sound bad, yeah.
Inductors are usually the more annoying part of a design, so one tends to prefer a CLC(LC..) format, with RC damping.
Also, have you considered simply making a longer filter? You'll get better attenuation with those 330uF's spread out amid, say, three 0.47uH's. Probably don't even need to be 330, unless there's a hold-up spec you're supporting (in which case, don't forget the diode on the front end, to prevent other loads from discharging it faster!).
Tim
jmw:
You're right, below 4 MHz that 2 uH isn't doing much when in series with 50 ohm. Now I understand what you meant by the transfer function isn't everything: the textbook of course doesn't mention the measurement is taken at the LISN port with its 50 ohm impedance at frequency!
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