| Electronics > Beginners |
| Oscilloscope oddities |
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| JohnPen:
I did a quick set up to check/modify your results. Using a FY3200S to produce an 8v sine (100 Hz) connected to a germanium diode (OA47) followed by a 10K load. This was monitored by a X10 probe on a DS1054 unlocked set for DC coupling. The resulting trace showed a very close to half wave rectification. 4.8 horizontal divisions rectified sine to 5.2 divisions ~zero volts. The amplitude of the half sine reduces by the diodes forward voltage drop. This should be close enough to demonstrate half wave rectification in a simple way. Also fit a switch to reverse the diode to enhance the demo. |
| rsjsouza:
How are you making the connections? Do you have a diagram? Using a simple 1N4007 and a 1k resistor connected as below, I get the following waveform: 1N4007 DS4014 ┌────────►│───────┐←───────┐ ╔═════════════╗ │ ↑ │ │ ║ ┌───┐ ☼ ║ HP3314 │ │ < │ ║ │ │ º º ║ 4Vpp (~) │ > R │ ║ └───┘ ☼ ☼ ║ 100Hz │ │ < 1kΩ │ ║ ch3 ch1 ║ │ │ > │ ╚═════════════╝ │ │ │ └───┘+ │- │+ │- └───┼─────────────┘←──────────────┘ │ │ │ ↑ │ │ │ └─────────────────────────────┼──┘ │ │ └─────────────────────────────────┘ |
| Ian.M:
--- Quote from: Mr. Scram on August 13, 2018, 08:03:53 am ---Note that displaying a fully rectified wave on a regular oscilloscope it troublesome. As far as I know you need an active probe for that, or apply a bit of math function trickery. A half wave should be possible, though. --- End quote --- If you are using a bench scope with conventional probes and a bench signal generator, you need a coupling transformer as the signal generator output to the rectifier must be fully floating so the negative side ot the DC output can be grounded without shorting half the diodes in the bridge. For demo purposes with small signals a 600R line isolating transformer from a dead modem will probably do the job as long as you don't let it saturate. Otherwise, you need to use differential probing techniques and avoid grounding the negative side of the DC output. |
| tester43:
I am guessing: you will not see zero on AC because of minimum forward voltage of the diode. |
| JohnPen:
An extra thought if you have a function generator like the FYxxx series which has 2 separate independent outputs. Using both outputs on say 100 Hz, with 8v sine waves on each, set one output offset by 180 degrees. Connect the 2 outputs to a bridge rectifier's AC inputs, load the output of the rectifier with a 10K load and monitor rectified 200 Hz with your scope. |
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