Electronics > Beginners

Full bridge rectifier shows wrong curve on scope

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GreyWoolfe:

--- Quote from: StillTrying on January 05, 2020, 11:28:16 pm ---It looks like the bottom-right diode is in the wrong row ?

--- End quote ---

I see the same thing, the bottom right diode is not connected to anything.

petert:
I used a microcontroller with an integrated DAC to generate a 50 Hz sine wave. I made sure to use a capacitor and checked it was really going from 1.65V to -1.65 V (approximately).

Since the µC is powered through a 4.5V battery (and not plugged into USB or anything else), it should be isolated from everything else.
Probing is as before, and the result is the same as with the signal generator (with some lightly different distortions). i.e. half the waveform is missing, reversing the probing polarity shows the negative half of the waveform.

So far only putting a small transformator between the signal generator and the rectifier input has worked. Odd.

petert:

--- Quote from: GreyWoolfe on January 06, 2020, 01:05:33 pm ---
--- Quote from: StillTrying on January 05, 2020, 11:28:16 pm ---It looks like the bottom-right diode is in the wrong row ?

--- End quote ---

I see the same thing, the bottom right diode is not connected to anything.

--- End quote ---
I replied to that already, it's just an unfortunate picture issue, but correctly connected in the real circuit.

petert:

--- Quote from: StillTrying on January 06, 2020, 09:28:07 am ---It should be easy enough to trouble shoot it just the with scope's GND on the generators GND, the +Ve sine peaks should be on the +Ve bridge output and the -Ve sine peaks on it's -Ve output. Simples!

--- End quote ---
Connect both the scope and signal gen ground together, directly (I suppose), and then?

Edit: I connected both together, and when I do neither of the bridge rectifier outputs produce any signal (0V DC).
If I keep the circuit as in the breadboard picture, and red wire to probe black to scope gnd, then I get V(br+), if I connect the black wire to the scope probe, and the red to scope gnd, then I get V(br-).

Not sure what conclusions to draw from that though...

petert:
Okay, another test!

I did differential probing (as suggested earlier in this thread).

I connected all probe grounds to the signal generator ground. One probe is on the positive bridge rectifier output (red/orange wire), i.e., scope channel 3 (pout). The negative output (black wire) is connected to scope channel 4 (nout).

pout - nout (ch3-ch4) is shown as fwb.

The differential waveform still does not look what it should like. Maybe that could give a clue?




(I also tried different diodes to make sure they are not the problem.)

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