Fluke's single phase diode rectifier - Page 1
Forum section: electronics / beginners

author: Martini
author_rank: Regular Contributor
timestamp: March 26, 2016, 09:19:54 pm
content: Hi,Fluke is showingrectified ACwaveforms in their document about true RMS and I was wondering what it exactly meant.http://en-us.fluke.com/training/training-library/measurements/electricity/what-is-true-rms.htmlSomeone care to explain to me?How do you get that AC signal from (I guess) a pure sine wave?

author: Andy Watson
author_rank: Super Contributor
timestamp: March 26, 2016, 09:44:25 pm
content: Where, exactly, are they showing the rectified sinewave?The diagram at the top of the page has the caption of "non-sinusoidal", which it is! Possibly due to a phase-controlled unit/module/device.The other instance, in the table, shows the output of a rectifier that has a significant forward voltage drop, i.e. no, zero output voltage for portions of the sinewave. I guess there is some artistic licence creeping into this diagram since you would not expect to see both positive and negative parts of the cycle as the output of any real-life rectifier circuit.

author: Martini
author_rank: Regular Contributor
timestamp: March 26, 2016, 10:04:03 pm
content: Quote from: Andy Watson on March 26, 2016, 09:44:25 pmThat's what caught my attention. And that's the one they called "single phase diode rectifier"

author: uncle_bob
author_rank: Unknown
timestamp: March 26, 2016, 10:07:31 pm
content: HiThe "rectifier" stuff is looking at the current on the AC line.Bob

author: onlooker
author_rank: Frequent Contributor
timestamp: March 27, 2016, 02:16:17 am
content: QuoteApparently, some level of liberal artistic rendering is the likely explanation. The "single phase..." diagram is likely meant for the voltage waveform after the plain old single diode rectifying (half bridge), for which all the half waves are on the positive side.The same can be said for their diagram of 3 phase diode rectifying. It is more likely meant for the waveform after half bridge rectifying 2 of the 3 phase lines, for which all rectified waves should be on the positive side. Though, the flat part depicted in their diagram is a lot longer than it should be (60 degrees) and the middle of the M shaped wave should not reach 0.

author: Martini
author_rank: Regular Contributor
timestamp: March 28, 2016, 10:35:45 am
content: Quote from: uncle_bob on March 26, 2016, 10:07:31 pmOh, that makes sense

author: onlooker
author_rank: Frequent Contributor
timestamp: March 28, 2016, 12:53:03 pm
content: QuoteThe AC line current waveform would look like this if you have a full bridge rectifier with very large forward voltage drop.

author: Martini
author_rank: Regular Contributor
timestamp: March 28, 2016, 02:18:23 pm
content: Now I'm lost again.Why wouldn't it look like this if you had a half bridge rectifier and a DC load?

author: onlooker
author_rank: Frequent Contributor
timestamp: March 29, 2016, 02:35:43 am
content: For a half wave rectifier, the conducting phase is between 0 and 180 degrees, or, within the "positive" half of the waveform.That is, the half waves will only be taken from the same "positive" side. This will show up as positive half waves spaced with flat lines for the voltage after the rectifier, and for the current for both before and after the rectifier (the same current measured at different locations) .

author: Martini
author_rank: Regular Contributor
timestamp: March 29, 2016, 03:23:21 pm
content: You're right, I was confused