1kH Synthetic Inductor


Inductors can be
mimicked quite easily using operational amplifiers. The circuit shown
here was developed to have an inductance of 1000 H (say, one thousand
Henry) with good damping. Using this design you can build a resonant
circuit with a center frequency of less than 1 Hz. The slow behavior
allows you to use conventional measuring instruments to investigate the
circuit in real time. The circuit can also be used as part of a filter
design. Opamp1 operates as an Integrator, Opamp2 as a difference
amplifier.

The output voltage of Opamp2 is equal to the voltage drop across R1
and P1, which is proportional to the output current. This voltage is
differentiated by Opamp1, C1 and R2. The net effect is that the circuit
behaves as an inductor. P1 allows adjustment of the inductance value. P2
allows adjustment of the Q factor of the coil by altering the symmetry
of the difference amplifier and with it the stability of the circuit.


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