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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
Most Helpful 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
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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.
upload_2017-4-15_21-56-14.png
 

DerStrom8

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

ronsimpson

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Most Helpful 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.
upload_2017-4-16_8-15-53.png
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.
 

audioguru

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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

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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
Most Helpful 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:
I deleted C4 already, but can you advice something with comparator?
 
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