triangular wave generator and astable multivibrator circuits using opamp

[vineeth gk]

can any one help me out with my proteus simulations. iam using proteus 8. iam unable to get output for triangular wave generator and astable multivibrator using opamp ua741. i hav attached the circuit diagram of both tat i used in proteus. plz anyone debug the errors i made

 

[FvM]

Both circuits are correct, apparently some fault in Proteus design entry and circuit parameters.

 

[vineeth gk]

can u help me sort tat out.

 

[Audioguru]

A real oscillator starts by amplifying its own noise. But your simulation program has no noise.
The oscillator will start if you can add some offset voltage at an input.

 

[FvM]

A real oscillator starts by amplifying its own noise. But your simulation program has no noise.
The oscillator will start if you can add some offset voltage at an input.

The problem exists only for a linear oscillator, not for relaxation (or hysteretic) oscillator like the present one.

 

[Audioguru]

I think a SIM program causes this oscillator to sit calmly with the opamp inputs at 0V. Noise, input offset voltage or a good swift KICK would get it going.

I betcha that even a two-transistors multivibrator with equal value parts also will not start oscillating by itself in a SIM program.
I tried it in LTspice IV and it does not start oscillating unless the program is set for "UIC, Skip The Initial Operating Point Solution".

 

[FvM]

I think a SIM program causes this oscillator to sit calmly with the opamp inputs at 0V. Noise, input offset voltage or a good swift KICK would get it going.

I betcha that even a two-transistors multivibrator with equal value parts also will not start oscillating by itself in a SIM program.
I tried it in LTspice IV and it does not start oscillating unless the program is set for "UIC, Skip The Initial Operating Point Solution".

You are right. There must be an initial disturbance. E.g. a DC offset and skip initial transient solution, or a kick-start pulse.