Simple diode rectifier but a puzzling waveform

[S185149]

Sine wave through a diode, full bridge with FR207's, expecting to see that classic half sine wave but ...

As you can see from the attached screenshot, I'm getting significant rounding of the waveform in the negative half of the cycle. The rounding gets worst as the frequency goes up. I could use some words of wisdom on what is going on.


Thanks,

[Ash]

Hi,

Are you sure you have the diodes in the correct orientation? You aren't accidentally feeding the AC into the DC junctions?

Where is your scope ground(s)? You're not providing a path through them to somewhere you shouldn't be? What's the AC source, is it a centre-tapped transformer or is it a single winding? Maybe a photo / schematic of your setup would help.

Cheers,
Ash.

[S185149]

I'm pretty sure I didn't screw it up. I know the FY3200 has that floating ground issue so that is why I grounded the scope on the negative lead of the sig gen.

[amspire]

You need a load on the rectifier output. Otherwise, the diode capacitance affects the waveform.

[S185149]

Ah. I was suspecting capactance effect but didn't know from where. Thanks for clueing me in. When I throw a resistor across the output, the bottom flattened out nicely and at one diode drop below ground which makes sense now.

Thanks again.

[batteksystem]

Seems to be parasitic capacitance.

[Damianos]

Ah. I was suspecting capactance effect but didn't know from where. Thanks for clueing me in. When I throw a resistor across the output, the bottom flattened out nicely and at one diode drop below ground which makes sense now.

Thanks again.

I think that this is not normal.

[S185149]

Ah. I was suspecting capactance effect but didn't know from where. Thanks for clueing me in. When I throw a resistor across the output, the bottom flattened out nicely and at one diode drop below ground which makes sense now.

Thanks again.

I think that this is not normal.

When I saw the trace go below ground in the bottom half of the cycle, it was puzzling to me. But because of where I have to place the ground lead for the scope, I had to redraw the circuit to visualize what was happening during the bottom half of the cycle. When I did that, I saw the probe and the ground clip were on opposite sides of a diode so it would make sense for it to read one diode drop below ground.