# Raise voltage up above 0

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#### LarsNor

##### New Member
I have triangle signal in my circuit, i know how make it lower ( put capacitor), but i have no idea about opposite step.

What should i add for rise it up ( 0-10V)

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#### AnalogKid

##### Well-Known Member
The output of U11 is centered about GND, but the output of U13 is just DC at the opamp's maximum positive saturated output value. Are you asking about adding a DC component to the output of U11 before it goes to U13? This can be done with a coupling capacitor and some bias resistors.

ak

#### LarsNor

##### New Member
The output of U11 is centered about GND, but the output of U13 is just DC at the opamp's maximum positive saturated output value. Are you asking about adding a DC component to the output of U11 before it goes to U13? This can be done with a coupling capacitor and some bias resistors.

ak
Hi. Yes, i'm asking about point with green marker. As you can see, i added capacitor, but voltage goes down, can you explain how can i raise it up?

#### ronsimpson

##### Well-Known Member
If you made the (+) supply +10V, the negative supply = 0V, and what was gnd now is +5V.
Now your output will be from +1V to +9V.
This is close to what you want.

#### LarsNor

##### New Member
If you made the (+) supply +10V, the negative supply = 0V, and what was gnd now is +5V.
Now your output will be from +1V to +9V.
This is close to what you want.
View attachment 105527
It's perfect. How you calculated that it should be from +1 to +9 V. What is equation can i use if i need from 0 to +5 V?

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#### LarsNor

##### New Member
sorry for that. mb you know another method, without playing with power supply?

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#### DerStrom8

##### Super Moderator
I would have just used a summing amplifier and an adjustable DC voltage supplied by a potentiometer.

#### ronsimpson

##### Well-Known Member
It's perfect. How you calculated that it should be from +1 to +9 V. What is equation can i use if i need from 0 to +5 V?
The voltage circled in red sets the center of the wave form. Try setting this to 5.5V or 6V and watch.
R11 & R12 set the end points. I am doing this in my head so might be wrong. lol
Don't go much bigger. It will stop working close to 100k, and above.
R13 & C3 sets the slope. Volts/uS.

The voltage on the power supply pins (+5, -5 OR +10, 0V) should cover the output you want. (probably should be one or two volts larger in range than the output.

#### AnalogKid

##### Well-Known Member
What is the purpose of U13? What signal do you want at its output?

ak

#### LarsNor

##### New Member
What is the purpose of U13? What signal do you want at its output?

ak
i have triangle signal ~-4 - +4, but i need 0-5V, that's why i asked about elements of circuit, because if i change voltage i loose PWM signal after comparator

#### audioguru

##### Well-Known Member
The capacitor you added prevented a reference voltage on the (+) input of the 3rd opamp.

Your SIM program did not read the datasheet for the TL031 opamp:
1) The TLo31 opamp inputs do not work if they are within 1.5V from the -5V supply but your 3rd opamp has its (- ) input directly at -5V so it will not work.
2) The output of a TL031 opamp cannot go anywhere near the +5V power supply voltage, some will go only as high as +3V.

#### LarsNor

##### New Member
The capacitor you added prevented a reference voltage on the (+) input of the 3rd opamp.

Your SIM program did not read the datasheet for the TL031 opamp:
1) The TLo31 opamp inputs do not work if they are within 1.5V from the -5V supply but your 3rd opamp has its (- ) input directly at -5V so it will not work.
2) The output of a TL031 opamp cannot go anywhere near the +5V power supply voltage, some will go only as high as +3V.
It works perfect if i have power supply -5 - +5 V

#### audioguru

##### Well-Known Member
It works perfect if i have power supply -5 - +5 V
The stupid SIM might work but the real circuit will not work.
1) An opamp cannot work without a DC reference voltage on its (+) input within its common mode input voltage range.
2) The output of a TL031 and most other opamps cannot go anywhere near its +5V supply voltage.

#### LarsNor

##### New Member
The stupid SIM might work but the real circuit will not work.
1) An opamp cannot work without a DC reference voltage on its (+) input within its common mode input voltage range.
2) The output of a TL031 and most other opamps cannot go anywhere near its +5V supply voltage.
This circuit is usual Schmitt trigger+differntiator, nothing especially. I saw few videos where circuit worked

#### audioguru

##### Well-Known Member
Maybe the huge value of your capacitor C4 takes a few days to charge with the very low leakage current of the Fet-input opamp.
Here are the other problems with the opamp U13:

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#### LarsNor

##### New Member
Maybe the huge value of your capacitor C4 takes a few days to charge with the very low leakage current of the Fet-input opamp.
Here are the other problems with the opamp U13: