I am looking at the Q factor of certain inductors from the datasheet –
inductor datasheet
Now, I am trying to analyse the Q-factor for the 2.2uH inductor. The chart shays that the Q factor is 48 measured at a frequency of 7.9MHz. But, if I look at the graph it says a different picture. At 7.9MHz its is almost 70.
How is this possible ?
Also, my need is for the frequency range 300MHz and 2.4GHz (different inductors ofcourse).
So based on the graph the Q factor is not available for those frequencies. Do Q factors decay away to very low values after the peak or will it rise again at other frequencies ?
Best Answer
The graph shows the nominal or typical Q value that you can expect for a certain inductor at a certain frequency. Unfortunately not all these inductors will be identical, due to small variations in the materials and inaccuracies the Q will vary. Sometimes Q will be higher, sometimes it will be lower.
The table shows the minimum value of Q meaning that the manufacturer guarantees that the value of Q should never be lower than stated value (48 at 7.9 MHz).
Indeed for an inductor working at 300 MHz you will need a different type. No, the Q factor will not "recover" for higher frequencies. If there is a graph of the inductor's impedance over frequency you will see that the impedance will decrease over frequency at frequencies above the "peak Q" frequency so the inductor will behave like a capacitor ! That means that actually it does not matter what the Q is for higher frequencies as the Q is only relevant when the inductor behaves as an inductor.