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Circuit of rectifier

When I'm doing a simple half-wave rectifier with the set-up as shown above (Note: Diode D2 is not connected) and connected terminal 5 and 4 with positive and negative terminal of oscilloscope, this is what I get:

Generated trace: Terminal 5 and 4

Instead of getting a horizontal line in the second half cycle as the diode blocks the current flow in the opposite direction, I get a slanted line with a positive gradient. Can someone give me an explanation on why this happen in my experiment? I have only some basic knowledge about electronics and I'm unable to come up with a plausible explanation.

This is what I get when I connected oscilloscope to terminal 1 and 2, in case it helps:

Generated trace: Terminal 1 and 2


Edit: I uploaded the wrong picture for the my third one. I have uploaded the new picture.

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  • \$\begingroup\$ The oscilloscope's image rotation calibration may be incorrect. \$\endgroup\$ – Majenko Mar 20 '15 at 10:14
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    \$\begingroup\$ "Note: Diode D2 is not connected" that's why you're only getting half the cycles. \$\endgroup\$ – pjc50 Mar 20 '15 at 10:58
  • \$\begingroup\$ Yes I'm supposed to get only half the cycle. The question is why the second half cycle is a slated line with positive gradient instead of a horizontal one. \$\endgroup\$ – khtan Mar 20 '15 at 13:38
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I think you may have your oscilloscope set to block DC i.e. it is AC coupled to terminals 4 and 5. Try setting your scope input to DC.

As for your 2nd picture, you must be measuring somewhere different to where you believe you are measuring - double check your scope probe connections. Maybe what is visible is a fuzziness on the o-scope trace and this is at odds with your original trace that was clear. Maybe the ground point of your o-scope is disconnected or maybe it isn't a good photograph?

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  • \$\begingroup\$ Sorry I had uploaded the wrong picture for my 2nd picture. I have uploaded the new one. \$\endgroup\$ – khtan Mar 20 '15 at 13:37
  • \$\begingroup\$ @sniperkit2en that's OK and now makes sense - this is what you should see on points 1 and 2. Maybe you can confirm about the AC coupled or DC coupled scope probe? \$\endgroup\$ – Andy aka Mar 20 '15 at 13:38
  • \$\begingroup\$ it's AC coupled. But I don't have access to the equipment now until the next few days. \$\endgroup\$ – khtan Mar 20 '15 at 14:17
  • \$\begingroup\$ There's the problem - if you DC couple it then you will have a flat line between half cycles. An ac coupled scope will have a high pass filter set to maybe 1Hz and any constant dc values (other than zero) will be gradually forced towards zero. \$\endgroup\$ – Andy aka Mar 20 '15 at 14:38

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