The waveforms shown below are voltages taken across a 10 Ohm Resistor (pink) and an 1mH inductor (blue) in series with one another. The circuit is excited by a 1 kHz, 1 volt peak-to-peak sine wave. What is happening that causes the waveforms to flatten when the resistor waveform is at it's peaks? Someone suggested it had something to do with the ESR of the inductor. Is this correct? If so, how does it have this effect? If not, what is actually going on?

Here is a SPICE rendering of the schematic for good measure. But the waveforms shown above are not simulated, they are measured from a physical circuit.

  • \$\begingroup\$ Please include a circuit showing exactly what you simulated. Also any details about the models for the individual components. There's no way to explain your results in terms of ideal R and L components connected the way you described in your text. \$\endgroup\$
    – The Photon
    Oct 4, 2015 at 3:16
  • \$\begingroup\$ The components in question aren't ideal; the waveforms shown are physical measurements. I added that detail to the question to be clear. \$\endgroup\$ Oct 4, 2015 at 3:30
  • \$\begingroup\$ What was the voltage source? An arbitrary waveform generator? Does it have a maximum output current? \$\endgroup\$
    – The Photon
    Oct 4, 2015 at 3:34
  • \$\begingroup\$ Also, what instrument did you use to measure the voltages? Does it have a maximum input voltage? \$\endgroup\$
    – The Photon
    Oct 4, 2015 at 3:36
  • \$\begingroup\$ Its a USB generator. Its a component of a product Digilent makes called Analog Discovery (and its actually pretty awesome if you haven't heard of it). But anyway, The maximum current is around half an amp. There's a current monitor in the software and everything seems to be fine there. Its well within the input voltage range. I've tested the waveform generator output and nothing funny there either. \$\endgroup\$ Oct 4, 2015 at 3:41

1 Answer 1


ESR of an inductor is a linear circuit element and would not produce such behavior. What you have there is some severe non-linearity caused by some unknown element in your circuit.

E.g. the power supply that generates the 1 kHz voltage waveform could be drooping the voltage because it runs into current/power saturation. Perhaps there are some non-linear circuit elements that you did not draw but which are present in the actual circuit.

Try plotting the output voltage waveform. My suspicion is that you won't see a perfect 1 kHz sine wave. This would be especially true if you are using a signal generator to produce the signal. Signal generators are known to have very large output impedance.

  • \$\begingroup\$ The output looks good. I'm at a loss. \$\endgroup\$ Oct 4, 2015 at 3:43
  • \$\begingroup\$ thank you you're right. the non-linear behavior originated in the scope/generator, thank you. \$\endgroup\$ Oct 4, 2015 at 3:49

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