non microcontroller based 30khz PWM with full scale duty cycle

Thread Starter

vahid_22002

Joined May 29, 2014
6
Hello dear friends
It might be something odd, but I am looking for a low price design that can have a 30khz PWM output with a variable duty cycle.
What I have simulated so far is this method, but the simulation in Proteus doesn't work in 30khz output. Is it the problem with Proteus or something else is it? As for the opamp, I chose lm833. Omitting the third opamp will show the triangular output.
Your help is really appreciated.
 

ericgibbs

Joined Jan 29, 2010
14,207
hi v,
In LTSpice it is sometimes required that that an IC [ initial condition] be set before a circuit will oscillate, This is because as a sim it will be 'balanced' at power up, whereas in a practical circuit the component tolerances are sufficient to start the oscillation.

Is there a similar command for IC in Proteus. ??

E
 

Ian Rogers

Joined Dec 12, 2012
952
In proteus... Use a primative capacitors and put a kick button on the output of U1B ( to ground)

Also use a rail to rail opamp.. I used an LT118***** The LM833 works better..
 
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Thread Starter

vahid_22002

Joined May 29, 2014
6
hi v,
In LTSpice it is sometimes required that that an IC [ initial condition] be set before a circuit will oscillate, This is because as a sim it will be 'balanced' at power up, whereas in a practical circuit the component tolerances are sufficient to start the oscillation.

Is there a similar command for IC in Proteus. ??

E
It is not supposed to only be in a simulation, it is supposed to be on a board, so the initial conditions are all zero.
 

Thread Starter

vahid_22002

Joined May 29, 2014
6
In proteus... Use a primative capacitors and put a kick button on the output of U1B ( to ground)

Also use a rail to rail opamp.. I used an LT118
It is not really needed to have 0 and 100 percent, but 5 to 95 percent is sufficient for me. Moreover putting a key means to be manual. And this is not something desirable. It should be automated.
 

ericgibbs

Joined Jan 29, 2010
14,207
hi v,
This is what I see in LTSpice, used AD820 OPA',

Note : .IC = V(vo)=0
Does not run without IC..
E
Check my circuit for accuracy.


Update:
Added a ramped Vctl sim plot.

EG 861.png
 

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