# Quick question about Triangular Generator

Discussion in 'General Electronics Chat' started by Dritech, Nov 9, 2014.

1. ### Dritech Thread Starter Well-Known Member

Sep 21, 2011
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5
Hi all,

When I Google Triangular Generator, all circuits provided are formed from a schmitt trigger connected to the negative input of an integrating circuit. This causes the triangular output to be inverted from the square wave.
Is it possible to connect the input of the integrator circuit to the positive terminal instead? Will this work? and do I have to use a different feedback layout?

Any help would be appreciate.
Thanks.

2. ### Alec_t AAC Fanatic!

Sep 17, 2013
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No. If you need to invert the waveform then use an additional inverting opamp.

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3. ### Dritech Thread Starter Well-Known Member

Sep 21, 2011
756
5
Also, in the attached 2 steps, I can understand that (R2/R2+R2)Vsat changed to -(R2/R2+R2)Vsat
but what exactly happened to -Vramp? and how did R2 in the denominator changed to -R3?

I really cannot understand what happened in these 2 steps.

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4. ### Alec_t AAC Fanatic!

Sep 17, 2013
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Your circuit doesn't show a Vramp node. Presumably Vramp = V0 (the output of A2)?
R2 and R3 form a voltage-divider. The voltage at the top is V0', and at the bottom is Vo. Therefore the voltage across the divider is Vo'-Vo and so the voltage at P is V0 + (Vo'-Vo)*R2/(R2+R3).

Last edited: Nov 9, 2014

Sep 21, 2011
756
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6. ### Alec_t AAC Fanatic!

Sep 17, 2013
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The linked article has only 43 pages . I don't see those steps anywhere, nor R2 replaced by R3. 5.6 is the relevant section.
Ground is common; not Vramp (the A2 output). The text is confusing because the author uses '-Vramp' to denote the negative part of the triangle.

7. ### Dritech Thread Starter Well-Known Member

Sep 21, 2011
756
5
Hi,

Sorry I think it was another pdf. I cannot find the file, but I have this screenshot of the derivation. From this part I cannot understand how R2 changed to R3 in the numerator. Also, what happened to -Vramp?

8. ### Dritech Thread Starter Well-Known Member

Sep 21, 2011
756
5
Sorry forgot the attachment.

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9. ### Veracohr Well-Known Member

Jan 3, 2011
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Combine the two Vramp terms.

10. ### Alec_t AAC Fanatic!

Sep 17, 2013
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$-Vramp+Vramp\times\frac{R2}{R2+R3} = Vramp\times(\frac{R2}{R2+R3}-\frac{R2+R3}{R2+R3})=Vramp\times\frac{-R3}{R2+R3}$

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