Oscillator using BSN20

Discussion in 'General Electronics Chat' started by HansCA, Apr 24, 2011.

  1. HansCA

    Thread Starter New Member

    Apr 24, 2011
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    I have very limited experience at the transistor level in design. I need to make a simple oscillator out of R/C and BSN20 N-MOSFET. Low frequency 50 to 100 Hz. Can anyone suggest a circuit. Currently trying to implement an astable multivibrator using the BSN20 in a configuration as found in Question 7 of http://www.allaboutcircuits.com/worksheets/oscill.html. I know I have it wrong. I just don't know how to make it right. Thanks in advance for any and all suggestions.

    I have found this site extremely informative and helpful. Thanks for all the hard work.
     
    Last edited by a moderator: Apr 24, 2011
  2. Adjuster

    Well-Known Member

    Dec 26, 2010
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    I can't see anything on your link. Please post a picture of your schematic so that we can see what you are trying to do.
     
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  3. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I have corrected the link for you.

    Bertus
     
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  4. Adjuster

    Well-Known Member

    Dec 26, 2010
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    A MOSFET astable can have a pretty strong tendency to saturate both sides if the gate resistors are returned directly to a relatively big +rail voltage, to look like the BJT version. Lower bias voltage, by a potential divider or otherwise may help.

    Simulations of oscillators are also notorious for needing some type of starting kick, perhaps from a pulse source. In a symmetric oscillator like this, a tiny deliberate asymmetry can do the trick, combined with omitting the initial bias point calculation.
     
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  5. HansCA

    Thread Starter New Member

    Apr 24, 2011
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    I will try the bias process with a resistor on each leg of the gates to ground and put the gate a apx. 50% of available 3.3 Vdd.
     
  6. HansCA

    Thread Starter New Member

    Apr 24, 2011
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    Profile edited to include GMT -5 for time zone.
     
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