# 30khz triangle wave

Discussion in 'Homework Help' started by hobolo, Aug 12, 2013.

1. ### hobolo Thread Starter New Member

Aug 10, 2013
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Hi guys, i am trying to build a triangle wave oscillator 30khz using ua741 op amp. But i cant get the output, can anyone pls help me with the design? The circuit is the normal schmit trigger and integrator circuit combination. Can u guys tell me what values i shud use for the resistors and capacitor. I understand that the formula is given by f= (R2/R1)(1/4RtC).

2. ### studiot AAC Fanatic!

Nov 9, 2007
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Go for 3kHz with a 741, 30 is too high.

3. ### hobolo Thread Starter New Member

Aug 10, 2013
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but i need 30khz, because of my teacher. Is it possible to use 741 for 30khz?

4. ### studiot AAC Fanatic!

Nov 9, 2007
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You'd be very lucky to find a 741 with that frequency response.

However post your circuit for comment and check that you have built it correctly.

Aug 10, 2013
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6. ### Ramussons Active Member

May 3, 2013
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A 741 has a 0.5 V/uS slew rate and, therefore, should be able to generate a 30 KHz triangular wav with an amplitude of about 8 V p-p.

As studiot said, let's have the schematic.

Ramesh

Aug 10, 2013
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8. ### bountyhunter Well-Known Member

Sep 7, 2009
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There are better op amps like LF356 for example..

9. ### wayneh Expert

Sep 9, 2010
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Have you never heard of "plug 'n' chug"? Pick a capacitor and calculate the R values. Repeat until all R and C values are practical.

But, I think you'll struggle to get 30kHz from the 741. Try getting 3kHz working first.

10. ### studiot AAC Fanatic!

Nov 9, 2007
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The gain bandwidth curve for a 741 shows an open loop gain of about 30 at 30kHz.

Is this enough?

I doubt it.

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11. ### RichardO Well-Known Member

May 4, 2013
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Ramussons wrote:

If the op-amp is used as the comparator then it has to have a slew rate many times faster -- more than 10 V/uS to keep from rounding the peaks of the triangle wave too badly.

12. ### Ramussons Active Member

May 3, 2013
520
76
Hmmmmm ... you have a point

Ramesh

13. ### bountyhunter Well-Known Member

Sep 7, 2009
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Which is why I recommended the LF356 in my first post (12V/us).

14. ### hobolo Thread Starter New Member

Aug 10, 2013
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ok thanks for the help guys, I will change the op amps. What other factors do I need to consider inorder to generate 30khz triangle wave. Is the circuit diagram I am using capable of producing 30khz triangle wave.

15. ### wayneh Expert

Sep 9, 2010
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You need to specify the degree of accuracy you need to define the "triangle". A square wave is a high-error triangle. A sine wave is closer. An RC charge-discharge profile might be still closer. The 741 might produce something resembling a triangle, I'm frankly not sure. What do you really need?

16. ### hobolo Thread Starter New Member

Aug 10, 2013
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Now I am using LF356 op amp but I cant get any output. I used R2=10k, R1= 5.6k, Rt= 1k and C = 0.1microF. I am not getting any output waveform with this and I am still using the same schmitt trigger + integrator circuit. Is my values of my resistors and capacitors wrong?

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17. ### studiot AAC Fanatic!

Nov 9, 2007
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First are you getting any output from the square wave?

Second if you disconnect the square wave generator from the integrator, does the integrator work with a suitable DC input voltage?

18. ### JoeJester AAC Fanatic!

Apr 26, 2005
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How did you determine the values? Did you plug those values into the formula to see if your choices were correct?

I suggest you get a copy of OpAmps for Everyone. It's available from Texas Instruments and there is your oscillator of choice in that pdf file.

Can you post the diagram of your circuit ... as built ... since the one you keep posting does not have a Schmidt trigger.

The circuit diagram you keep displaying should work just fine. If you've breadboarded the circuit, take a photo....

Last edited: Aug 16, 2013
19. ### hobolo Thread Starter New Member

Aug 10, 2013
7
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no i am not getting any output from the square wave.