+ Post New Thread
Results 1 to 2 of 2
  1. #1
    Junior Member level 2
    Points: 680, Level: 5

    Join Date
    Dec 2010
    Posts
    22
    Helped
    0 / 0
    Points
    680
    Level
    5

    Voltage Controlled Oscillator Design

    Click image for larger version. 

Name:	asdas.jpg 
Views:	22 
Size:	115.7 KB 
ID:	88763

    The circuit above should work as a VCO. I want to create a triangle wave with 1 kHz. I have no idea why it doesn't work though. The transistors doesn't seem to be going in forward-biased region independent of what I do.

    Any advice?

    •   AltAdvertisment

        
       

  2. #2
    Advanced Member level 5
    Points: 22,863, Level: 36
    barry's Avatar
    Join Date
    Mar 2005
    Location
    California, USA
    Posts
    4,369
    Helped
    970 / 970
    Points
    22,863
    Level
    36

    Re: Voltage Controlled Oscillator Design

    First of all, I'm not sure what those two opamps on the input are for, all they do is supply +/10 to your transistor buffer. As far as I can see, and maybe I'm missing something, is the output(emitters) of the transistors drives the input to an integrator(U3A). The voltage into this integrator is dependent on the state of U4A. It has NOTHING to do with that 10V from the first stage, although I believe that's what you THINK should happen.

    Regardless, your NPN transistor is, in fact, forward biased, as you can see by the Vbe=.67V. Your problem is that you've got too much (WAAAAAY too much) feedback around your comparator. Try changing R6 from 1K to maybe 50K.



--[[ ]]--