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LM317A: Using the LM317A with High Voltage

Richard Brown1
Prodigy 20 points
Part Number: LM317A

Based on the below comment from page #1 of the LM317A datasheet, can the LM317A be used with rectified 120Vac or 240Vac as long as the Vi-Vout differential is not exceeded?  

What is the maximum voltage this part can be used with in the "floating" mode?

"Because the LM317A regulator is floating and detects only the input-to-output differential voltage, supplies of several hundred volts can be regulated as long as the maximum input-to-output differential is not exceeded. Exceeding the maximum input-to-output deferential will result in short-circuiting the output."

I'm considering using his part as a cost effective constant current source for a high power LED string (1A or less). 

  • 0
    TI__Mastermind 22610 points

    Q1: " ... can the LM317A be used with rectified 120Vac or 240Vac as long as the Vi-Vout differential is not exceeded?  ..."

    A1: As long as long as the max input-output voltage differential is not exceeded, Yes.

    Q2: "... What is the maximum voltage this part (LM317A) can be used with in the "floating" mode? ..."

    A2: There is no specification for "maximum input voltage" or maximum output voltage", the only limitation is for the "maximum input-output voltage differential" of 40V.