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SN75451BP failure

Richard N
Prodigy 20 points

Using a SN75451BP to shunt current away from a fiber optic transmitter or else allow it to turn on (if the 75451 is off and open). Unit returned from the field and the 75451 is clearly destroyed. The case came apart upon removal and the internal structure is melted and shows signs of severe dissipation. The +/-15V and 5V supplies also had issues. The 5V regulator was only generating 2.5V instead of 5V so the 75451 Vcc was only 2.5V. Could this have led to excessive dissipation inside the chip and the eventual failure? or is something else more likely and should I look elsewhere? Thanks for any help.

  • 0
    TI__Guru**** 164476 points

     Richard,

    The low 5V voltage would have resulted in low base drive to the SN75451 output transistor. Therefore the transistor might not saturate when turning on and would result in high power dispassion, IOUT * VOUT. (less IOUT than usual, but much higher VOUT when on).