How Do You Connect Vcc+ and Vcc- in a TL072 OpAmp Circuit?

In summary, the conversation discusses how to connect a battery to the Vcc+ and Vcc- pins of an op amp in a sallen-key high pass filter. It is suggested to use either two batteries or one battery with a voltage divider. However, the input signal must vary around the half-battery-voltage point and the output is limited by the supply voltages. It is also mentioned that certain op amps have limitations on how close their inputs can get to the rails.
  • #1
rusty009
69
0
Ok, sorry for this basic question, I am currently designing a sallen-key high pass filter using a TL072 opAmp, with the schematic shown below,

SallenKeyLP.gif


This circuit is connected to a piezo trasnducer whose signal I wnat to amplify. I was wondering, what do I connect to the Vcc+ and Vcc- pins of the op amp ? Should I connect a battery to each pin or is one of them (Vcc-) the ground ? I am aware this is a very basic question but I was just wondering. Also, say I put 18 volts into the amplifier, will this turn my amplified signal into 18 volts ? Thanks.
 
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  • #2
The simplest arrangement is to have two batteries with one battery's positive and the other battery's negative going to the opamp and the other battery connections going to ground.

You can also use one battery and put a voltage divider across it to get a ground point.
Like this:
[PLAIN]http://dl.dropbox.com/u/4222062/LM324.PNG

However, this does take extra current from the battery for the voltage divider.

And it means the input signal must vary around the half-battery-voltage point (not around ground) or be capacity coupled into the opamp.

The output of the opamp is limited by the supply voltages, but it will be equal to the size of the input signal (usually measured in peak to peak volts), multiplied by the gain of the amplifier.

If this comes to more than the supply voltage, then the signal output will get distorted.
 
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  • #3
And keep in mind that the TL074 style opamps do not let their inputs get very close to the rails. For +/-15V power supplies, the input common-mode range is only +/-11V. So you have to keep your inputs at least 4V away from the rails, which often limits your design...

http://www.datasheetcatalog.org/datasheet/texasinstruments/tl074.pdf

You can look at more modern (and more expensive...) CMOS opamps -- some let you get the inputs and output very close to the rails.
 

1. What is an OpAmp and how does it work?

An OpAmp, or operational amplifier, is an electronic circuit component that amplifies the difference between two input signals. It typically has a high gain, high input impedance, and low output impedance. It works by taking the difference between the two input signals and amplifying it to a higher output voltage.

2. How do I choose the right OpAmp for my circuit?

Choosing the right OpAmp for your circuit depends on several factors such as the required gain, input and output voltage ranges, and frequency response. It is important to carefully consider these specifications and select an OpAmp that meets your circuit's requirements.

3. What is the difference between an inverting and non-inverting OpAmp configuration?

In an inverting configuration, the input signal is applied to the inverting terminal of the OpAmp, while the non-inverting terminal is connected to a fixed reference voltage. This results in an output signal that is inverted from the input. In a non-inverting configuration, the input signal is applied to the non-inverting terminal, and the output is amplified without inversion.

4. How do I calculate the gain of an OpAmp circuit?

The gain of an OpAmp circuit can be calculated by dividing the output voltage by the input voltage. In an inverting configuration, the gain is equal to the ratio of the feedback resistor to the input resistor. In a non-inverting configuration, the gain is equal to 1 + (feedback resistor / input resistor).

5. How can I prevent oscillations in my OpAmp circuit?

Oscillations in an OpAmp circuit can be caused by improper wiring, incorrect component values, or a lack of stability in the OpAmp itself. To prevent oscillations, make sure the circuit is properly designed and wired, and use decoupling capacitors to improve stability. You can also try using a different OpAmp with better stability characteristics.

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