Problems regarding Oscillator design..

Thread Starter

Laguna

Joined Apr 1, 2010
5
Hi all
I am dealing with some problem here.

Regarding the attachment below..

I can't seems to get a triangular wave..

May i know whats the problem I'm facing?
 

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Audioguru

Joined Dec 20, 2007
11,249
The problem is that Multisim does not know if it is coming or going.

The integration capacitor is supposed to charge and discharge with ramps but your schematic has a ramp in only one direction.

Since the 555 does not produce a perfect square-wave (its timing is 5 periods positive then 4 periods to ground) then the triangle-wave will be only negative with the ramps at 5 periods and 4 periods.
 

Thread Starter

Laguna

Joined Apr 1, 2010
5
Thanks for replying
So what kind of modification should i do on my circuit?
Is there anything to correct it?
 

Audioguru

Joined Dec 20, 2007
11,249
A 555 needs a trimpot and two diodes to allow you to adjust its duty-cycle so its output is a perfect square-wave. Then the output of the intergrator will be triangle waves.

I use an opamp as a Schmitt trigger to make the square-waves that feed an integrator.
 

Thread Starter

Laguna

Joined Apr 1, 2010
5
Do u mean that the
Schmitt Trigger is connected to output of the 555 to get a 50% duty cycle of square wave?
 

Audioguru

Joined Dec 20, 2007
11,249
Do u mean that the Schmitt Trigger is connected to output of the 555 to get a 50% duty cycle of square wave?
No.
Get rid of the high current non-square-wave 555 and replace it with a symmetrical opamp (like an MC33171 or MC34071) Schmitt trigger instead. When the triangle wave's voltage gets high enough then it switches. When the triangle wave voltage gets low enough then it switches in the other direction. Then the triangle wave is perfect.
 

Audioguru

Joined Dec 20, 2007
11,249
If you filter a square-wave or triangle-wave well enough then the output is a sine-wave. You don't need a triangle-wave.
A 4th-order or 8th-order switched capacitor lowpass filter IC has very low distortion when fed a square-wave.
 
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