Op-amp driving a transformer

Discussion in 'The Projects Forum' started by srikanth.remudala, Dec 22, 2014.

  1. srikanth.remudala

    Thread Starter New Member

    Nov 30, 2014
    9
    0
    Hi guys,
    Please find the attachment. Here an op-amp is driving a transformer. I am feeding a FFSK signal (audio band) at TP1 and when probing it at various TPs. The following is the signal condition observed in a scope:
    • at TP2: distorted and voltage drop.
    • at TP3: distorted and voltage drop.
    • at TP2 with load (600Ohm) removed: signal wobbling. (could be due to floating).
    • at TP3 with load (600Ohm) removed: signal wobbling. (could be due to floating).
    What could be the issue.
    I need a neat signal (with out distortion) at the load. A level drop is OK.
    Can any one help.

    Thanks & Regards,
    Srikanth.
     
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,504
    380
    hi,
    Set TP1 signal voltage to zero and disconnect the transformer from the OPA output and measure TP2 voltage, it will be Vdd/2.!
    What is the DC resistance of the 1:1 transformer primary winding.?

    Then re-connect the transformer to the OPA, with TP1 still at zero, re-measure the DC voltage on TP2.

    E
     
  3. srikanth.remudala

    Thread Starter New Member

    Nov 30, 2014
    9
    0
    Hi Eric,
    Yes the voltage at TP2 when transformer is removed is VDD/2 due to the voltage divider used at the non-inverting terminal of op-amp. And after I connected back the transformer, the voltage at TP2 is still VDD/2.
    By the way, I tried matching the transformer input impedance by placing a resistor capacitor series combination ( R=600Ohm , C = 0.1uF). But still the situation is same.

    Can we suspect the transformer. The transformer is actually present in another device. I need to interface my hardware (op-amp ) with this device which is said to have a 600Ohm 1:1 transformer at the input.

    Can we suspect any think from the transformer point of view...??
     
  4. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,504
    380
    hi,
    Please measure the DC resistance of the transformer windings, let me know.

    I have simulated the circuit, using a 1uF and 500R in series with OPA output and transformer primary, it works OK in simulation.
    The rt1 input signal is a DialTone wave file.

    E
     
  5. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    You should not apply any DC to the transformer since that will saturate it. You can block the DC by using a capacitor in series with the transformer input.
     
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