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OPA192: OP-AMP is driving npn transistor and inductive load, OP-AMP Output is always saturating

Part Number: OPA192

The following circuit is designed in TINA, But the output of OP-AMP is always saturating and not converging according to the load, Please Suggest solution

The designed circuit and simulation results are attached below

The designed circuit and simCurrent_Drive_Ckt.TSCulation results are added here.

  • Amit,

    One problem is the drive required on to output your target current.  A bipolar transistor is a current controlled device.  The collector current is the base current multiplied by the current gain (Ic = hfe x Ib).  The emitter current is approximately equal to the collector current.  The TIP29 has an hfe between 15 and 75 with a 1A load.  The base current would have to be 1A/15 = 66mA.  Your op amp can't drive that and also your 1k series resistor would need 66V to drive that.  You should consider a Darlington transistor or a MOSFET.  The attached presentation covers your application in detail.  Look at pages 146 for a Darlington example, and 170 for a MOSFET example.

    Design and Apps Current Sources_AFA REV A (1) (1).pdf

    Best regards,


  • Thank you Art, 

    I will check this reference.