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When building a half-wave rectifier with a capacitor filter for my electronics lab, there was significant clipping at the peaks of the input signal. When looking at the .csv file pulled from the oscilloscope, these "clippings" are filled with #'s. I interpret this as the oscilloscope isn't getting any data at these peaks and is just attempting to fill in the blanks on the trace. What is the reason for this?

The setup is a simple half-wave rectifier using a 1N4148 diode, a load resistance of 2.2kΩ, and 500Ω. The input signal is a 5V peak-to-peak sine wave with a frequency of 60Hz. The goal is to adjust the capacitance from 100μF to obtain a ripple factor of less than 5%. I have noticed the most significant clipping when using a 500Ω paired with a 669μF capacitor. I attached an image below of the traces and LTSPICE schematic as well as probe locations.

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As you can see, the clipping is around ~0.75 volts at the peaks. Is there any decent explanation for this? The oscilloscope is a 4-channel Keysight DSOX variant (I don't have access to the exact model right now but it is similar to the DSOX2024a). The function generator is a Siglent technologies waveform generator (likewise, don't have access to the exact model).

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  • \$\begingroup\$ What oscilloscope is this? Does it not have adjustable range? \$\endgroup\$
    – Miron
    Commented Mar 19, 2022 at 22:31
  • \$\begingroup\$ @Miron It is a Keysight DSOX. I don't have access to the oscilloscope at the moment, but it is similar to the DSOX2024a. I updated the question. Yes it has an adjustable range. \$\endgroup\$ Commented Mar 19, 2022 at 22:45
  • \$\begingroup\$ @TonyM Yes, thank you! that explains the #'s. \$\endgroup\$ Commented Mar 19, 2022 at 22:48
  • \$\begingroup\$ You're very welcome. Have converted my comment into an answer, please don't forget to accept answers that answer the question. Thanks. \$\endgroup\$
    – TonyM
    Commented Mar 19, 2022 at 22:57
  • \$\begingroup\$ Draw the schematic. Where do you probe? How does the input look? \$\endgroup\$
    – Linkyyy
    Commented Mar 19, 2022 at 23:04

2 Answers 2

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The clipping is a result of the output resistance of the function generator.

The majority of function generators have 50 ohm output resistance. So there is effectively a 50 ohm resistor in series with a perfect voltage generator.

When the diode conducts the current flowing will cause a significant voltage drop across that output resistance resulting in the the clipping that you are seeing.

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  • \$\begingroup\$ This seems to explain it quite well. I added the 50ohm resistance to my LTSPICE simulation and it introduced quite a bit of clipping at that peak. \$\endgroup\$ Commented Mar 19, 2022 at 23:15
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If you’ve pulled the .csv into Excel, then Excel displays '#'s for certain datatypes when a column isn't wide enough for the value it contains.

Try double-clicking on the column divider up on the cell names row. That makes the column wide enough for the widest item in the column.

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