I only get one half wave on my oscilloscope.Should be full wave - Page 1
Forum section: electronics / projects

author: jacobixx
author_rank: Newbie
timestamp: May 04, 2017, 10:02:45 pm
content: I made this full wave rectifier on my breadboard.All the 4 leds are lite up working.I have a resister and cap on the output.When I hook up my oscilloscope it shows onehalf wave.When I flip the leads I get one half wave upside down.Don't know why I don't get full wave. It seems to be hooked up right. The ohms resisteris 220 and 1000 uf cap. It's the simple bridge type circuit.

author: grumpydoc
author_rank: Super Contributor
timestamp: May 04, 2017, 10:14:19 pm
content: A circuit diagram, photos of what you have built and a screen dump or photo of the oscilloscope trace would be useful, as well as details of the oscilloscope settings.

author: David Chamberlain
author_rank: Frequent Contributor
timestamp: May 04, 2017, 10:18:49 pm
content: Agree with grumpydoc that a little more information would be helpful. Where is the AC input before your rectifier coming from?A resistor and LED in series with your AC input will basically produce a half wave rectifier and the LED will light up, perhaps your actually just bypassing the rectifier completely?Is this what you have?

author: electr_peter
author_rank: Unknown
timestamp: May 04, 2017, 10:20:37 pm
content: Schematic or picture of full setup is needed to determine the cause.What is driving bride rectifier? Is it mains or function generator?I would guess that scope is shorting half of sinewave through common ground because AC source is not isolated. If this is the case, you would need either isolated AC source or use differential probing.

author: Zero999
author_rank: Super Contributor
timestamp: May 04, 2017, 10:34:24 pm
content: Have you connected one side of the input to the bridge rectifier to one side of the DC output?Are you probing the AC side as well as the DC side?Do you have an earthed signal generator on the AC side and earthed oscilloscope on the DC side?If any of the above is true, then this is exactly what you should expect to happen.

author: janoc
author_rank: Super Contributor
timestamp: May 04, 2017, 11:23:40 pm
content: Quote from: Hero999 on May 04, 2017, 10:34:24 pmWhat you have unhelpfully left out is explaining to the OP that he is most likely shorting out half of the bridge with the scope probe ground lead.@jacobixxHere is a video explaining the issue:

author: Zero999
author_rank: Super Contributor
timestamp: May 05, 2017, 07:48:27 am
content: Quote from: janoc on May 04, 2017, 11:23:40 pmYes, I did leave that bit out but I disagree with the part about being unhelpful. The idea was for the original poster to figure that part out for themselves. Sometimes just spoon-feeding someone the entire answer is not helpful because if they get used to it, they won't learn to think for themselves. No one ever had to explain this to me, when I was a beginner. I had to work it out for myself.Fortunately, the bridge rectifier is a fairly straightforward circuit to understand. Here's an animation showing the polarity of current in a bridge rectifier.http://www.reuk.co.uk/wordpress/electric-circuit/bridge-rectifier/

author: jacobixx
author_rank: Newbie
timestamp: May 05, 2017, 08:22:15 pm
content: Thanks hero999 that's exactly what I have,I do have a resistor and 100 uf cap accrossed the out put.I use the grd with the other input lead on output.I looked at the top vedio and I didn't understand what he did to finally get full wave on oscilloscope.

author: Zero999
author_rank: Super Contributor
timestamp: May 06, 2017, 05:08:29 pm
content: Quote from: jacobixx on May 05, 2017, 08:22:15 pmHe removed the channel monitoring the AC.Look at the part of the video showing the 0V of the 'scope probes connected to both the AC and -V parts of the bridge rectifier.

author: testian
author_rank: Regular Contributor
timestamp: May 06, 2017, 08:40:58 pm
content: For testing, you could remove your 100 uf cap and only attach the probe to the output. Then you should get the typical full wave rectifier waveform.All grounds of your oscilloscope inputs are connected. It is easy to short something out when measuring and both are connected.