I am using an OPA547 high voltage and high current op-amp.

  • V+ = 15 V
  • V- = GND or -15 V
  • Ilim is shorted with V-
  • Vout has a fb resistor of 1K. The output load is a 50-ohm resistor
  • Vin+ = 0 V (GND)
  • Vin- is connected to 2 Vpp 1 KHz sine with dc offset -2.5 V through a 1K resistor

enter image description here

I am using it as inverting amplifier with unity gain. The expected output is supposed to be a sine signal with 2 Vpp with an offset of +2.5 V, but the actual output is

Case i) V+ = +15 V and V- = GND

enter image description here

Case ii) V+ = +15 V and V- = -15 V

enter image description here

Can anyone guess what could be the problem?

  • 2
    \$\begingroup\$ Vin+ must be at a higher voltage, you have grounded the gate of one side of your diff. pair and left no room for the current source since everything is at 0 volts. To give you a hint, measure the voltage at your virtual ground. \$\endgroup\$
    – Designalog
    Commented Oct 15, 2022 at 12:40
  • 1
    \$\begingroup\$ One detail you should disclose is the frequency of the input sine wave. \$\endgroup\$ Commented Oct 15, 2022 at 12:43
  • \$\begingroup\$ There is a schematic editor built in to the editor. It is fairly easy to use. The icon looks like components in parallel or Ctrl-M is the hotkeys. \$\endgroup\$ Commented Oct 15, 2022 at 12:57
  • \$\begingroup\$ @ErnestoG The voltage at Vin+ is 0 V. Do you suggest connecting Vin+ to GND through a 1k resistor? \$\endgroup\$ Commented Oct 15, 2022 at 13:07
  • \$\begingroup\$ @KishoreKumarS, no. What you need to do is define the common-mode voltage of your input. I asked for the voltage at V-. \$\endgroup\$
    – Designalog
    Commented Oct 15, 2022 at 13:16


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