I am working on a project in which I am trying to measure current from a current transducer (SCT 013-030). I want to convert the output to VDC and connect it to a smoothing capacitor and load resistor. However, the bridge rectifier that I currently have to use (DF005M) appears to be a half bridge, not a full bridge rectifier.
I am seeking some guidance in how to best verify what type of bridge rectifier I have? Because the output signal of the CT is so small, I used a function generator to simulate a stronger input signal (60Hz, 20Vpp sin wave). I connected that input wave to the two '~' pins of the DF005M rectifier. When I connect the '+' pin to the purple channel of my oscilloscope, I understandably get only the positive parts of the wave. However, what confuses me is that when I connect the yellow channel to the '-' pin, I only read the negative parts of the wave.
It was my understanding that a full bridge rectifier inverts the negative parts of the wave. Thus, I am confused as to why a negative signal is even getting through in the first place...
Any guidance in properly implementing teh DF005M (or verifying the need for a different rectifier) would be much appreciated! I have searched online for customer reviews for the DF005M glass passivated bridge rectifier, but have not found any that discuss how to properly implement it. I can't even find manufacturer's resources that provide the internal circuit diagram for the component.
Thanks in advance for helping out a young mechanical engineer who is trying to learn about implementing rectifiers.
Neither the (-), nor the (+) of the bridge are directly connected to a ground in the circuit. However, one of the 2 alligator clips coming from each channel of the oscilloscope is connected to a common ground (the ground on the SDS 1102X oscilloscope).
I think I was able to figure out my problem. The two PP510 100MHz Oscilloscope Probes that I am using are "single-ended" probes, meaning they measure the difference between a single point and ground. Thus, the oscilloscope was showing exactly that (see initial post above). What is needed in order to appropriately measure the output of a full-bridge rectifier is a "differential" probe, which measures the difference between any two points. Because I do not own any differential probes, I simply applied the "MATH" function on the oscilloscope to plot the difference between the two channels. The picture attached shows how the potential difference between the two channels, is in fact a typical rectified signal. In summary:
Conclusion 1: A differential probe must be used to measure the output of a rectifier properly. Measuring either the (+) or the (-) pin with a single-ended probe only tells half the story, as they measure a single point relative to ground. This was a helpful website I found that helped explain the importance and difference between different oscilloscope probes.
Conclusion 2: The DF005M rectifier is in fact a full-bridge rectifier.
That's an excellent point! As a mechanical engineer with no previous training in power transforming though, I have enjoyed the exercise in understanding how rectifiers work.
Do you know what the technical characteristic for the "threshold voltage of the diodes" would be on a rectifier's datasheet? Now that I've connected the circuit to the CT's output, the rectified signal's magnitude is much smaller (as expected). However I'm having issues when I try to implement a small resistor (220 Ohms) in parallel to the smoothing capacitor: there becomes effectively no difference between the rectified and CT input signals. As you stated, I think it has to do with the rectifier's "threshold voltage," but don't know how to confirm that with the DF005M datasheet.
Common rectifier diodes, as in your bridge rectifier, have a threshold of ~0.45volt.
And there are always two in series in a bridge.
Your current sensor already has a burden resistor build-in, so don't use an external (220ohm) resistor.
Measuring current with a CT and the Arduino directly (no rectifier) has been done many times before.
You only need two resistors and a capacitor.
Google "Arduino openenergymonitor" for diagrams and code.
Leo..
Your scope probes will (or should have) have a shield or ground wire running up the test lead, usually terminated with an alligator clip. Connect probe tip to the + on the bridge and the shield to the - on the bridge. You will now see the expected positive going 1/2wave pulses at twice AC frequency.
