# Need opinion of phase compensation for inductor.

1. Oct 23, 2011

### yungman

I want to design a circuit that drive an inductor of 3H and internal resistance of 6K with the phase of the driving current and output voltage on the inductor it 180 phase difference at various frequency as shown in Fig 2. So I need a circuit that start to roll off the gain and create a phase lag at the same frequency of the coil break frequency and roll off at a single pole like the coil's zero.

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The way I calculate is the coil has a zero at $2\pi f L= 6000\;\Rightarrow \;f=\frac {6000}{2\pi L}=318Hz$. At shown in Fig 3, at that point the voltage phase began to lead the current from the collector of the transistor by 45 deg and eventually to 90 deg.

To compensate the increase of voltage across the coil and the voltage phase lead, I use a low pass and phase lag circuit to compensate. In Fig 4, I use a cap of 0.025uF in parallel to the 20K so the break frequency is $\frac{1}{2\pi f C}= 20,000\;\Rightarrow \; C= \frac 1 { 2\pi f R}= 0.025uF$.

Please give me you opinion whether this is correct or any suggestion.

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