Electronics > Beginners
Full bridge rectifier shows wrong curve on scope
wraper:
Unless you use differential probe or disconnect mains earth from either signal gen or oscilloscope, you are simply shorting 2 out of 4 diodes through earth. It's the same thing why you should be cautious where you connect ground clip when measuring stuff. Of course it does not apply is your signal gen is not earthed (like some old low tech stuff).
hermitengineer:
--- Quote from: petert on January 05, 2020, 08:33:17 pm ---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:
(Attachment Link)
Without load resistor:
(Attachment Link)
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?
--- End quote ---
The left vertical diode in that picture is in the wrong orientation.
petert:
Using a small transformer with 3 turns on each side (I got it from a CFL lamp) it finally works as it should, but only for higher frequencies around 1 Mhz.
Is there a way to make the signal generator floating with a non frequency dependent way?
Interestingly, disconnecting the signal gen and scope from earth (as I mentioned above) had no effect.
I'll try to generate a signal with a microcontroller, powered by a battery and see if that has the same isolating effect.
--- 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 ---
It looks like this on the picture, indeed. I tried to make a reasonably sharp photo, but that part looks odd due to the angle (and closeness to the black "plug" of the red lead). The real circuit is correct in this location, however.
Jwillis:
Your orientation looks correct. I would check that each connection is seated well in the board and there are no breaks in the board it's self . Did you check each diode was functional.
wraper:
--- Quote from: petert on January 06, 2020, 12:24:10 am ---Interestingly, disconnecting the signal gen and scope from earth (as I mentioned above) had no effect.
--- End quote ---
Don't you have any data or some other cables connected to them?
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