Hi

I have a 555 timer producing a 600khz (roughly) 50% on 50% off square wave signal signal. This is fed into a integrator but The output is constantly -11v with smalll variations

I've tried altering the valuses of c1 and r1 with no luck

anyone have any idea whats going on?

Ive posted my showcad3 circuit in a zip too

Attached Images

integrator.JPG (133.8 KB, 15 views)

Attached Files

integrator.zip (808 Bytes, 0 views)

 

Maximum frequency of the 555 is 500kHz and you don't need a dual supply, a single +V rail will do. I don't like the componant values used in you differentiator, 100R is a bit too low, and .1 uF looks far too big, the output will be so too small to measure, try 470pf and 1k.

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looks more like a triangular wave with your component values but the triangular wave is -10.986v to -11.008
the output should be +/-11v

I was planning to use the cmos version of the 555 from what I've found it's limit is around 1mhz

 

That's not a differentiator, that's an integrator. And you can't run a true integrator "open loop". It will rapidly run off to one rail or the other, depending on input duty cycle and voltage levels. That's what you are seeing. If you want a triangle wave and a square wave, do it in a feedback loop as you said you would do in this thread.
Tell us again why you need a function generator at such a high frequency.

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Ron

 

when I originaly calculated the frequency of the secondary coul I made a mistake, it was 600 instead of 60khz

As for why I am not using the previous circuit, I could not get it to operate above 7khz

 

The circuit below (either version) runs at about 45kHz in simulation as drawn. You need to remember to tie unused LM393 inputs to the negative supply voltage (GND or vee, depending on which version you use), and to connect the unused TL072 as a voltage follower, with the noninverting input connected to the vcc/2 divider, or to GND, depending on which version you use. You also need power supply decoupling capacitors.

Attached Images

	fct gen sch.PNG (26.5 KB, 11 views)
	fct gen waves.PNG (26.3 KB, 5 views)

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Ron

 

problem solved the op amp was not operating fast enough,

solution: just use an resistor and capacitor connected to ground, If anyone wants me to I will post the circuit

 

I would like to see it.

__________________
Ron

 

here you go

both files need to be in the same folder

what do you think?

Attached Files

555 pwm circuit.zip (1.9 KB, 7 views)

 

I congratulate you on coming up with a working circuit.
However, I do think you have used way more parts than you need to get an inferior "triangle" wave. You don't need the push-pull emitter followers. You don't need another 555 just to invert a square wave.

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Ron

 

this circuit will eventually be used as part of a contol system for an h bridge, that is why there is a second 555

 

I didn't say you don't need an inverter. I just mean I think a 555 is overkill, and has more propagation delay, than a simple transistor inverter. However, it does use fewer parts!

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Ron

 

thanks for the suggestion of a transistor inverter, that's now replaced the second 555 as for the push pull emmitters they are required to get the triangular waves to match, without them the peaks are at different amplitudes

 

Thanks for all your help Ron

I've posted the completed circuit in case you were interested in how it finally ended up

Attached Files

FINISHED PWM CIRCUIT.zip (2.3 KB, 5 views)

 

Could you post a .gif/.png/jpg version please?

__________________
I also post at the following sites:
http://www.stop-microsoft.org http://www.heated-debates.com
Screen name: Aloone_Jonez
And http://www.silicontronics.com, same screen name as here.