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OPA541: OPA541 Single Supply Operation

Sujith Kallara
Prodigy 155 points
Part Number: OPA541
Other Parts Discussed in Thread: TINA-TI, OPA549

Hi,

As per the information from the datasheets, I was using OPA 541 in the Single Supply configuration (+36V and GND). But in order to get the proper output, I need to apply biasing voltage at the input terminals of the Op-amp. Especially in the non-inverting configuration, I need t to apply -5V (V2) in the inverting pin.  If I'm using a -5V in the circuit, then there is no advantage in going with the single supply configuration. Any solution to replace this -5V.

Thanks in advance.

  • 0
    TI__Guru* 93105 points

    Hello Sujith,

    I set your OPA541 circuit up in TINA-TI to check the DC node voltages as a first step. Below you can see what I obtained. Please check and make sure the voltages are what you expect from your design. A quick check of the voltages applied and the stage gains made on paper agree with the TINA voltage results. 

    If the -5 V source is indeed required at the upper OPA541 non-inverting voltage path that might be satisfied with an inverting voltage DC-DC converter, which would take a positive supply voltage and invert it to a negative voltage. The downside is it would require an additional IC and its several passive components.

    Regards, Thomas 

    Precision Amplifiers Applications Engineering

    OPA541_Inv_NonInv_01.TSC

  • 0 in reply to Thomas Kuehl
    Prodigy 155 points

    Thank you Thomas for your valuable reply.

    These were the requirements;

    The input signal (sine wave) has a frequency of 13.5Hz with a VPP of 15 volts. It also has a DC level of 7.5V. This signal is passing through inverting and non inverting amplifier configuration at the same time. (Both these configurations have gain 2).

    The following is the expected output.

    I'm, attaching a TINA design file with this reply which is done using OPA549. We are getting the required output while using OPA549. But when we replaced it with the OPA 541 the output changes. The biasing conditions are the same.

    OPA549.TSC

  • +1 in reply to Sujith Kallara
    TI__Guru* 93105 points

    Hi Sujith,

    You did change the circuit a bit from the first one. The -5 V source was removed from the input circuit of the lower op amp input circuit, and the resistive divider values were changed in the upper op amp input circuit. The DC output voltages obtained with those two changes would result in a both op amp outputs being at approximately +15 V as the simulation indicates. 

    The issue that you will run into with any operational amplifier, OPA541 or OPA549 included, is they have a limit as to how close to the supply rails the output can swing. The clipping in the waveform indicates that the output can't swing any closer to the negative rail. How close they can swing is affected by the load current they are asked to deliver. The higher the load current the further from the rail the maximum will be. If you need the amplifier to swing all the way to 0 V, then the V- power pin would have to be powered by a negative supply several volts below 0 V.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    TI__Guru* 93105 points

    Hello Sujith,

    Do you understand my explanation? Do you have any more questions about your OPA541/OPA549 circuits? If you have the information you need please go ahead and close this e2e thread.

    Thanks, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    Prodigy 155 points

    Thank you Thomas for the support.