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UA78: Unable to draw current

P SUBRAHMANYA ADIGA5
Prodigy 80 points
Part Number: UA78

Hello,

I have made small power supply of 15V using 7815. A 230V to 18V transformer followed by a bridge rectifier and followed by a filter. The output of the filter is given to 7815. A capacitor is also used after 7815. The circuit is giving output  of 15V when it is no load and lightly loaded(around 20 mA). But for little higher loads, the output voltage is dropping. The datasheet says that we can draw till 1.5A. But I am unable to draw even 100 mA at constant 15V. Why is this happening? What could be the issue.

Thanks,

-P S Adiga 

  • 0
    TI__Guru 55940 points
    Hi P S Adiga,

    You are correct that UA78 is designed to source up to 1.5 A to its load. In order to help debug, please provide a scope shot of Vin, Vout, and if possible Iout. Is it possible that your upstream supply is current limited?

    Very Respectfully,
    Ryan