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TL074: TL074 OP-Amp strange behaviour

Parameshwara Bhat
Intellectual 290 points
Part Number: TL074
Other Parts Discussed in Thread: , TL084, TLV9004, TLV9054, TLV9064, TLV9002

There is a working circuit where I am using MCP6044. I happened to test TL074 in the circuit and had error. I was surprised as by specifications and being an op-amp, the output was completely unexpected.

To probe further, I made the circuit schematic in LTspice, first using generic op-amp and then TL074 sub-circuit. The generic op-amp result was very close to values obtained with mcp6044. The results of simulation with TL074.sub was more or less the same as I obtained with the part TL074 running in circuit.

I am attaching both the images. The circuit is besides. Why inv and ninv inputs are not close in value to each other in the case of TL074 ? With universal op-amp, every inv, ninv inputs are very close in value.

It appears TL074 needs some special connection. Can anybody here point out ?

Thanks in advance,

Parameshwar

  • 0
    Guru 140200 points

    Hi,

    if you use the TL074 and not the TL074H (!), then please keep in mind that this OPAmp needs a minimum supply voltage of 10V and the input voltage must stay 4V away from the supply rails. See section 6.6 of datasheet of TL084. The TL074 is no rail-to-rail Opamp.

    (Unfortunately, TI has modified the datasheet of TL074 and have totally ruined the "recommended operating conditions". Oh dear, it was so nice and clear in the old version and now it's total chaos. The TL084 and the TL074 are nearly identical, if not completely identical. But they extremely differ from the H-version which is a completely different chip. I don't understand why they put the H-version into the same datasheet as the good old standard version. This will inevitably lead to confusion and has already...)

    Kai

  • +1
    TI__Mastermind 19612 points

    Hello Parameshwar, 

    Considering Kai's comments and that the supply voltage is low (5V), I recommend trying a rail to rail amplifier in its place, please repeat with the TLV9004. Depending on the frequency of the input signal of your design, you may need a higher bandwidth alternative, in which case I recommend TLV9054 or TLV9064. 

    Please let us know the results of the substitution. 

    All the best,
    Carolina 

  • 0 in reply to Caro Walter
    Intellectual 290 points

    I cannot immediately test with any of the amplifiers you suggest as they need import. But testing with TI's spice models, the result is what I get with mcp6004.

    Thank you.

  • 0 in reply to kai klaas69
    Intellectual 290 points

    Thank you for pointing out.

    My circuit cannot apply -5V. But changing simulation supply to +5v - (-)5v makes not much difference to final output. The inputs even with negative feedback as in my attached scheme, start diverging. But if I substitute with rail to rail (for ex.TLV9002 spice model), the two inputs start converging and the output is equal to what I am getting with mcp6004. It appears there is a fundamental difference to the way non_rail-to-rail  op amps can be used.

    PB

  • 0 in reply to Parameshwara Bhat
    Guru 140200 points

    Hi,

    have you kept in mind that the input voltage must be kept 4V away from the supply rails with the TL074? So, with a supply voltage of +/-5V the input voltage must not exceed +/-1V.

    Kai

  • 0 in reply to kai klaas69
    Intellectual 290 points

    Yes, But I seem to have made some other error.

    I re-tested just now. See the new attachment. After +5 - (-)5 supply, in simulation at least, I get nice response even with 2.5V input now. (This was 0.1 V this morning in my simulation ). This I will test tomorrow on my circuit board.

    Best Rgds, PB

  • 0 in reply to kai klaas69
    Intellectual 290 points

    I have tested on PCB. If +5V, -5V supply are given TL074 works correctly with 2.5V at the input (ninv1 in the uploaded images).

    Thank you for pointing in the right direction.