Full wave rectifier with AD8036

Discussion in 'General Electronics Chat' started by Nick_F, Jul 10, 2011.

  1. Nick_F

    Thread Starter New Member

    May 10, 2009
    4
    0
    Hi All,

    I built a full wave rectifier using a AD8036, based on the diagram from the spec sheet of AD8036/AD8037. I made a nice PCB, I used for decoupling the 100nF capacitors and 10uF/25V tantalum caps. I used a sinewave signal generator and tested with various frequencies from 1kHz to approx 100kHz. Checking with the oscilloscope on the input/output, I noticed the input gets a DC offset, while the output is strongly assimetrical for the two halfs of the rectified sinewave. Eventually I got some decent output by placing a 100ohm resistor between input to ground and changing RG (resistor between Input and pin2 of IC) from 274ohm to 200ohm. You can check image AD8036_FWR1.jpg.
    When I used the original circuit, as described in the spec sheet, the rectified output looked like in AD8036_FWR2.jpg.
    I tried connecting my sinewave generator through a 100nF capacitor, just to make sure the offset is not from my generator and the waveform still remained bad. The IC is new (I tried two) and the resistors are 100ohm, 271ohm and 272ohm (instead of 274ohm).
    So how should my setup be in order to get the expected results from the schematic published? I expect the diagram to work with AD8036 as well, not only with AD8037.

    Regards,
    Nicolae
     
  2. Nick_F

    Thread Starter New Member

    May 10, 2009
    4
    0
    I managed to use the AD8036 Spice model and the simulation shows a similar result with my experimental results. That means the sinewave generator must have the capability to maintain zero offset at the input of the rectifier. A capacitor placed in series with the input of the rectifier will cause a shift of the signal at VIN node and therefore a strongly assimetrical output. A resistor placed from input to ground (or even to -5V) will help bringing the offset closer to zero.

    Regards,
    Nicolae
     
    Last edited: Jul 11, 2011
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,386
    1,605
    Schematic?
     
  4. Nick_F

    Thread Starter New Member

    May 10, 2009
    4
    0
    Hi Ernie,

    The schematic and some description can be found in the spec sheet for AD8036/AD8037. I took a screenshot of the schematic and I'm adding it in here.

    Regards,
    Nicolae
     
  5. Nick_F

    Thread Starter New Member

    May 10, 2009
    4
    0
    I added a buffer built with LT1028 and the new circuit performs reasonably (at least in simulations), even when the source is coupled via a capacitor. New diagram is attached.

    Regards,
    Nicolae
     
Loading...