LR low pass filter!!!

Thread Starter

Thao Vu

Joined Apr 27, 2017
10
Hi everybody!!
I am having confusing regarding of the LR low pass filter.
Base on my simulation on the LTspice, i am seeing that the output voltage starts attenuating at about 2MHz. (attachment 1)
However, on my actual experience, i am seeing Vout starts increasing when Frequency is at about 391KHz (scope 2), you can see Channel 2 voltage is slightly greater than channel 1 voltage, and Vout keeps increasing (max voltage = 24V) until frequency is about 1MHz, then Vout start decreasing.
It seems to me it can behave like a band pass filter, but some how the Vout is able to climp up linearly proportional with frequency.
I am curious the reason causing the voltage increase. How reality does the inductor behave in this circuit?

Channel1: input from Signal generator (5Vac)
Channel2: Output at resistor

Please advice to help me understand!!
Thank you
 

Attachments

ericgibbs

Joined Jan 29, 2010
14,130
hi Thao,
Please post your LTSpice asc file, we can then compare the response.
E

What is the resistance of the inductor.?
 

Thread Starter

Thao Vu

Joined Apr 27, 2017
10
Hi Ericgibbs
Attachment is my asc file.
Hope it works here.

The inductor is: 1mH
15ohms by using DMM.

Thanks for response.
 

Attachments

crutschow

Joined Mar 14, 2008
28,161
So for an accurate simulation here, you need an accurate simulation model of components, not just their ideal values.
Inductors in particular, have parasitic resistance and capacitance that can significantly affect their operation.
 
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