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.

 

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/worksheet/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.

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.

 

Hello,

I have corrected the link for you.

Bertus

 

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.

 

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.

 

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