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I tried to improve the Q factor for a tank in a LRC parallel circuit by a factor of 30. To do that I used an inductance that is 30 times smaller. To keep the same resonant frequency, I replaced the capacitor with another one that is 30 times greater. According to the math, this should work.

When I implemented the circuit, I found out that the Q factor is only 16 times greater. Not what I expected. The resonant frequency remains unchanged in the new circuit. The output voltage is also lower than what I expected.

I don't know what is happening exactly. Any help would be appreciated. Thanks.

EDIT: I checked that the SRF of the components is much higher than the resonant frequency of the filter. So that I assume that the problem isn't related with this.

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  • \$\begingroup\$ There are real limits to Q due to non-ideal parameters you dot mention. What values & part numbers for RLC were used? \$\endgroup\$ – Sunnyskyguy EE75 Mar 3 '17 at 5:11
  • \$\begingroup\$ Show the circuit, and values, and operating frequency and test method. \$\endgroup\$ – Andy aka Mar 3 '17 at 10:15
  • \$\begingroup\$ Just because the inductance is 30 times smaller it doesn't follow that its resistance changes sufficiently. Its the resistance that limits Q. \$\endgroup\$ – JIm Dearden Mar 3 '17 at 11:35
  • \$\begingroup\$ In our circuit, the resistance can't be changed. We have to achieve that Q only by manipulating the tank. \$\endgroup\$ – Ivo Lodovico Molina Mar 7 '17 at 23:33
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I'm not sure how you have implemented that RLC parallel circuit (simulation or physical board), but the quality factor you've got is probably due to non-ideal behavior of some components.


For example, do you know the parasitic resistance of your inductor ? Maybe it's not approximately zero, which means you'd need to consider one more resistor in your circuit diagram. In this case, new equations would have to be deduced.

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  • \$\begingroup\$ I checked that the SRF of the components is much higher than the resonant frequency of the filter. So that I assume that the problem isn't related with this. \$\endgroup\$ – Ivo Lodovico Molina Mar 3 '17 at 11:53

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