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TL783: 2 TL783's in series to regulate voltage to 5V Thermal Issue

Mike Schmidt
Prodigy 10 points
Part Number: TL783

We are having a thermal problem with 2 TL783's in series. The devices get extremely hot and seem to go into thermal protection mode.

VIN+ ranges from ~20VDC to 150VDC

+5V_ADC is intended to be ~5.4VDC

  • 0
    TI__Mastermind 29260 points

    Hi Mike,

    The feedback resistors are loading down the series LDO's significantly.
    They place 14mA of load on each.  The first regulators see's all of that, so 28mA is loading it down.

    This means the first regulator is dissipating (150-25)*(28mA) = 3.6W. 
    This does not factor in the actual load of the circuitry.

    Without any additional loading the first regulator will rise 3.63W*25.3C/W = 92C if using the worst case data point in the datasheet.

    You would want to lower the current drawn by the feedback resistors to as much as possible to reduce power loss.  See figure 12 in the datasheet.  Additionally you may need a better heat sink if there is significant loading on the output.

    Additionally, the device is rated to 125V on the input.  The 150V input voltage is above the rated value, and we cannot guarantee the functionality of the component at this level.

    Thanks,

    - Stephen