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Full bridge rectifier shows wrong curve on scope

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petert:
Hello,

I am having a somewhat confusing issue. To make sure I did not make any mistake on the breadboard, when building my circuit, I built another one (slightly different setup) as described here:
https://www.instructables.com/id/Make-A-Bridge-Rectifier-From-Diodes/

But for some reason the same issue persists.

As input to the circuit I have a 50 Hz sine wave, generated by a function generator (which looks correct on the scope). But the output looks like it is only half wave rectified. I am a bit confused what could be going wrong.

With a load resistor:

Without load resistor:


The next test was to simply use a 4.5V battery as input, which shows as positive 4.5V DC line on the scope as expected. If I reverse the polarity, i.e., input -4.5V it also shows a positive 4.5V DC line on the scope, again as expected.

Any ideas what could be the issue?

StillTrying:
The input or/and output of a bridge rectifier has to be floating, the scope's GND and the function generator GND both being GNDed could explain it.

petert:
That sounds like a good guess. Any way I could make this work using a signal generator and a scope (without using a transformer)?


Edit: I made another test: I made sure the Gnd pins of both the scope and function generator are not connected to the wall plug, but there was no change. I disconnected the Gnd output of the signal generator to the circuit, but no change.

Finally I tested exchanging the scope positive and gnd leads, which resulted in a horizontally mirrored graph, i.e. all negative instead of all positive:

Fenton Bresler:
Where are you putting the probe and its ground lead in the circuit? They should be either side of the load resistor respectively. My guess is the probe ground is in the wrong place.

Full Wave Rectifier

P.S. Don't disconnect safety earth from your equipment.

alsetalokin4017:
 8)

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