Electronics > Beginners
Full bridge rectifier shows wrong curve on scope
petert:
Summary/solution:
As mentioned earlier, the breadboard circuit was correct, and the isolation was the main issue (multi-socket power outlet connects earth pins, even when the multi-socket as a whole is not connected to household's main earth).
Using a 10k load resistor in the bridge rectifier gave the best result, regarding noise and amplitude. Less creates some clipping, more creates distortion without increasing the amplitude. Using a probe with a 1X impedance setting (with the signal generator being isolated from earth ground/the scope's ground) instead of 10x, does not have any effect on distortion (contrary to what viewer comments claimed in the videos I linked right above this post).
Bridge rectifier output with 1K load resistor (and 10Vpp 50Hz sine input):
Bridge rectifier output with 10K load resistor (and 10Vpp 50Hz sine input):
Alternatives to isolating the signal generator's (or the scope's, or both) earth pin from the household's main earth are a UPS (uninterruptible power supply) or an isolation transformer. The former usually runs for some minutes only, the latter will still circumvent the RCD (that protects from dangerous currents through your body).
For differential probing using the math function: make sure both probes are set to the same impedance, and ensure the scaling on the scope (the software side) for the channels match the impedance of the attached probes as well.
Ysjoelfir:
Glad to hear that you solved the problem :)
alsetalokin4017:
:-+ :-+
Sneaky ground loops can be really puzzling. I have an old analog FG (Interstate/Racal F43) which has a very convenient feature: a chassis isolation switch. So it can be "normally" connected through the line cord to mains ground, or floated by simply switching the switch. But ground loops are sneaky: if you connect, say, a BNC patch cord from the isolated FG to the non-isolated oscilloscope so you can monitor the FG's output ... guess what.
StillTrying:
... guess what.
The BNC socket is connected to the chassis ? :-//
alsetalokin4017:
Ah... yes. Or no, depending on which BNC connector and which chassis you are referring to.
That is, on this FG, the power supply section _is_ connected normally, that is, the mains line ground is connected to the chassis. But the signal output section sends its output to the world through insulated BNC feedthru connectors that are _not_ electrically connected to the chassis at all.... unless the FG's isolation switch is in the normal "grounded" position. To keep idle fingers away from this switch the FG makers put it on the back panel, not the front.
So if you have this switch in the "isolated" position, neither of the signal section's outputs (BNC shield and inner conductor) are connected back through the chassis and mains line cord to the mains ground. Unless... you have connected the FG's output (or ext trigger, synch, whatever) BNC through a patch cable to some other instrument whose BNC connectors _are_ permanently actually grounded to that instrument's chassis which in turn is connected through its line cord to the mains ground and hence to all other stuff that is also connected to that mains ground. Like an oscilloscope probe "ground" reference clip. :-BROKE
Navigation
[0] Message Index
[*] Previous page
Go to full version