Op AMP UA741 Issue

Question

Can anyone suggest me a simple circuit to shift a 0V/5V sine wave (low freq, under 50KHz) to a sine wave -2.5V (when was 0) to +2.5 (when was +5V).

I have used a circuit for shift a 0V/5V sine wave (low freq, under 50KHz) to a sine wave -10V (when was 0) to +10 (when was +5V). The circuit used is shown below

The 2.5V is given through a 1K POT with pin-1 --> 12V and pin-2 --> 0V, middle pin of POT is connected to Inverting pin of OPAMP (at 10KOhm resistor). The output was -10 to +10V sine wave.

In another case, i need a output of -2.5 to +2.5V output when input is 0 to 5V sine wave. Using the same setup but changing the gain deciding resistors (i.e, Gain = 1), the offset voltage is applied through POT. the output was 0 to 5V which is same as input. can u please help me out.

what are your supply voltages? also, clear case of "drop the goddamn 741 and get an operational amplifier that works". — Marcus Müller, Sep 18 '20 at 13:24
look for a Opamp substractor circuit (or adder), where you substract a reference of 2,5 or add a reference of -2,5 — schnedan, Sep 18 '20 at 18:16

score 3 · Answer 1 · answered Sep 18 '20 at 13:40

If you change the two resistors to be the same you'll get -2.5V out with 0V in.

Now the problem is that the gain is +2 from the input. You want a gain of 1 so attenuate the input with a voltage divider.

schematic

^{simulate this circuit – Schematic created using CircuitLab}

If you simulate this you'll find that the output at 50kHz is a bit less than +/-2.5V because the LM741 has trouble keeping up with the relatively high frequency.

An almost equally ancient FET amplifier such as TL081 will keep up, or you can use something more modern that will work from lower voltage supplies.

score 3 · Answer 2 · answered Sep 18 '20 at 13:45

Can anyone suggest me a simple circuit to shift a 0V/5V sine wave (low freq, under 50KHz) to a sine wave -2.5V (when was 0) to +2.5 (when was +5V).

That just means removing the +2.5V DC offset of your 5 V peak-to-peak sine.

So, any highpass filter will do that. Simplest, CR high pass:

in----||---+----out
    1 µF   |
           - 
          | |
          | | 1 MΩ
           -
           |
           v
           GND

This has about 1 MΩ input impedance for any sine with a frequency above 0.3 Hz.

That's worse than what an opamp solution could have had, but frankly, since you're using a 741, you don't care. (that is not a desirable opamp)

Op AMP UA741 Issue

2 Answers2