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TLV8541: question on zero cross circuit

Jon Lavallee
Prodigy 50 points
Part Number: TLV8541

I am using the TI TLV8541DBVR in the circuit below.  As you can see the + pin is ground referenced and the – pin is an AC waveform that swings above and below ground.  Is this a legitimate use of the op amp?  I have a physical circuit and it’s working but was wondering if the circuit is good with having an input go below ground and that the op amp sees this as an acceptable input to flip the output

  • 0
    Prodigy 50 points

    i forgot to show that the op amp is powered by 3V

  • 0
    TI__Guru*** 145766 points

    Hello Jon,

    The circuit is a inverting amplifier with a gain of -10. Due to output VOL being ground, the circuit will also do half wave rectification. The inverting input voltage will be zero for VIN from 0V to -300mV.  The inverting input voltage will be positive for positive input voltage. So input at op amp doesn't go negative for small input and op amp  power on.  There will be a small delay for the output to leave VOL state after zero crossing; this is called overload recovery and is same concept as comparator propagation delay.

    R1 just adds noise and does not correct for input bias current. R1 = 1k will be less noise.

    Add about 10pF across R3 to help stability by compensating for parasitic capacitance at feedback node.