Voltage Follower Circuit Design: Input Too Low?

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In summary: A voltage follower opamp is used in this example to allow more power to be delivered to the load while maintaining the same voltage.
  • #1
cupidsd
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hi all,

I am trying to design a voltage follower circuit. The input is quite low, around 0.8 - 0.9V.

I tried an OP, whose power supply is +/-16V, then connected the output with inverting-input, and connected the non-inverting-input with my input (0.8 - 0.9V). But the output does not follow the input, and actually the output is around 1.4+V.

The circuit does not work well. I guess it is due to the input is too low. Am I right? So what OP should I use then? Any comment is welcome.

Thanks a lot.
 
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  • #2
That is a classic circuit and usually works OK. Small signals don't matter.

Some opamps require some DC path to ground from the input pins, so you could try a 100 K resistor from the non inverting input to ground. (The common of your two supplies could be called a ground.)
This is specified in the data sheets of the opamp or you can just look at the schematic diagram of the opamp's insides and look for open circuited bases on the input transistors. These have to have DC current flowing into them for the transistors to work.

Another test is to measure the input and output simultaneously. If they are the same, then the opamp is working properly. In your case, if the input is actually 1.4 volts when it should be 0.9 volts, then you need to work out why this is the case.
Electrolytic and Tantalum capacitors are pretty leaky and this can disturb high impedance circuits.

It would also be worth looking at the output with an oscilloscope. What measures as a small DC voltage on a DC meter could actually be quite a large AC voltage that happens to average as a small DC voltage
 
  • #3
You said +/- 16 volts.

Are there three leads on the supply, + - and common?

or just two?

Most opamps need "headroom" between signal and supply rails. 1.4 volts sounds like 741's common mode limit.

Try a LM324.
 
  • #4
I can picture a voltage follower op amp...V+ = V-...I get that. Vin = Vout.

The obvious question is why do you need the voltage follower? Why not just hook your original voltage source to your load?

Is the op-amp in this case perhaps allowing more power while maintaining the same voltage? In other words...is the op amp capable of delivering more amps in this case?
 
  • #5
Also, check the pins of the opamp chip to see if it has offset control.

This is simple to use and may give the effect you are having if it is not connected.
 

Related to Voltage Follower Circuit Design: Input Too Low?

1. What is a voltage follower circuit?

A voltage follower circuit, also known as a buffer circuit, is a type of electronic circuit that has an output voltage that is equal to its input voltage. It is used to isolate and buffer the input signal from the output, preventing any changes in the input from affecting the output.

2. What is the purpose of a voltage follower circuit?

The main purpose of a voltage follower circuit is to provide a high impedance input to a low impedance load. This helps to prevent loading effects on the input signal and ensures that the output voltage remains stable and equal to the input voltage.

3. What happens if the input voltage is too low in a voltage follower circuit?

If the input voltage is too low, the output voltage of the voltage follower circuit will also be too low. This can result in a loss of signal and distortion in the output. It is important to ensure that the input voltage is within the recommended range for the circuit to function properly.

4. How do I design a voltage follower circuit when the input voltage is too low?

To design a voltage follower circuit when the input voltage is too low, you can use an amplifier with a high gain. This will amplify the input signal and provide a higher output voltage. Additionally, you can use a voltage regulator to adjust the input voltage to the desired level.

5. How do I troubleshoot a voltage follower circuit with a low input voltage?

If you are experiencing issues with a voltage follower circuit where the input voltage is too low, you can check the connections and ensure they are secure. You can also use a multimeter to measure the input voltage and compare it to the recommended range. If the input voltage is still too low, you may need to adjust the circuit design or use additional components to amplify the signal.

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