Trying to understand voltage on rectifier

Discussion in 'General Electronics Chat' started by sebastianpatten, Nov 28, 2010.

  1. sebastianpatten

    Thread Starter New Member

    Nov 28, 2010
    Hi there,

    Im trying to get into electronics and the first thing I want to build is an AC to DC converter. I am using Tina to model the circuit first so I can fully understand it. However I am having trouble understanding two things.

    Looking at this allaboutcircuits page:

    I built the circuit at the top, basically a simple AC source that is a sine wave, Amplitute of 10 (I think this is volts) and Frequency of 50. I also have a diode.

    When i measure what the voltage is on the circuit it reads as -1.54e -18v. Why is this voltage so low? I can only think of that because of the diode, one cycle of voltage is not being allowed past the diode. But i dont get the huge difference of 10v in and reading the low reading.

    Also when I look at the oscilloscope, I would expect to see half of the full sine wave when looking at the circuit with a diode as the diode. But when I look at it, it looks like i see the full sine wave. Why is that?

    The diagram on the top of the allaboutcircuits page looks like it only shows half of the sine wave.

  2. SgtWookie


    Jul 17, 2007
    It would help a great deal if you posted an image of your Tina-TI schematic, and/or uploaded the simulation file.

    What value did you assign to the load resistor?

    What diode did you use?

    So many questions can be answered by posting a schematic. It eliminates ambiguities, and will get you answers much more quickly.

    .PNG format is preferred; the files are of small size, not "blurry" like .jpg files, and no additional software is required to view them other than a browser.
  3. sebastianpatten

    Thread Starter New Member

    Nov 28, 2010

    Thanks and here you go:

    I dont understand why the oscilloscope's wave doesn't look like the one on the top of this page:

    It looks like it goes to +3 ish volts to -3 ish volts.

    Also why when i run the app does the dc voltage look so tiny?


    Many thanks!
  4. sebastianpatten

    Thread Starter New Member

    Nov 28, 2010
    Any input on this? I'm new to electronics but don't understand why the waveform goes to negative voltage and why the voltage when measured in DC is so small.
  5. retched

    AAC Fanatic!

    Dec 5, 2009
    Try reversing the diode to see if tina responds to that.

    Also, what is the signal to start with?

    Try measuring it with no diode and show results.

    Add a ground to the circuit also. It may just be a simulation error because there is no assigned ground.

    Many spice packages will not run without a defined ground.
  6. sebastianpatten

    Thread Starter New Member

    Nov 28, 2010
    The signal is a 10V sine wave.

    Does what I am expecting sound reasonable? I don't want to get the wrong end of the stick regarding the ac waveform.

    Also the ground point is interesting. Is Tina crappy software?

    It seems like a lot of the circuits I have seen recently have had ground. Why would you need ground when you have a closed circuit?
  7. mik3

    Senior Member

    Feb 4, 2008
    I don't know if Tina is not good but using PSpice or LTSpice will give you good results.

    The ground may be needed as a reference point for the measurements.

    Try to put a ground and a resistor for a load.