I was trying to do a simple full bridge rectification. There is a strange problem. The oscilloscope does not show the rectified waveform in the negative cycle. The input is applied from a Keysight waveform generator. I did try to change the oscilloscope and waveform generators but these measures did not work. The diodes have no problems and work fine individually.

Could anybody please guide or point out the reasons why this is happening? Well, when I try to use one diode to check the unidirectional flow of current i.e half-wave rectification, it works fine but the polarity of the negative cycle does not change as shown in the figure below.

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  • \$\begingroup\$ Does this answer your question? Full Bridge Rectifier Oscilloscope Reading \$\endgroup\$ – JRE Jan 8 at 9:23
  • \$\begingroup\$ You have a shared ground between the signal generator and the scope. Clipping the scope ground to the rectifier output causes the problem. Take a look at this question and answer for a full explanation. \$\endgroup\$ – JRE Jan 8 at 9:25
  • \$\begingroup\$ So now I just unclip the grounds of function generator(and piezo) and the oscilloscope. Then I get a sine wave similar to input with a volatge drop of the diode. The negative cycle does not change the polarity. \$\endgroup\$ – Niharika Gogoi Jan 8 at 10:11
  • \$\begingroup\$ Where on earth are you connecting a piezo(whatever) to this circuit? What good did you think adding random parts would do? \$\endgroup\$ – JRE Jan 8 at 10:13
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    \$\begingroup\$ Piezo is used as a voltage generator. Then why does the question state: The input is applied from a Keysight waveform generator. If you ask a question, provide accurate information and include a schematic, yes even if the schematic is "obvious". -1 for providing inconsistant information. \$\endgroup\$ – Bimpelrekkie Jan 8 at 10:50

The generator and oscilloscope already have a ground reference via mains plug earthing

Thus connecting generator to bridge input and oscilloscope to bridge output already shorts out the diode that is between generator and scope grounds.

So when one of the diodes is now shorted out, one of the remaining unshorted diodes will now conduct the negative part of the waveform directly to ground.

  • \$\begingroup\$ So how do I resolve this problem? I also used a piezo across the rectifier as input, the negative cyle still remains unrectified. \$\endgroup\$ – Niharika Gogoi Jan 8 at 9:33
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    \$\begingroup\$ That's a whole another question with no simple answer without knowing why it is a problem and why it needs to be resolved? If this is school work, you should ask your instructor what is the correct way, as we have no clue how your instructor wants this to be resolved. \$\endgroup\$ – Justme Jan 8 at 9:35
  • \$\begingroup\$ @NiharikaGogoi: Unclip the ground wire from your scope probe to the rectifier - and read the question and answer I linked to. \$\endgroup\$ – JRE Jan 8 at 9:35

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