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power supply rebuild

Discussion in 'Power Electronics' started by jvdbossc, Dec 27, 2018.

  1. jvdbossc


    Jan 27, 2012
    Is it possible to use a 1 amp lm317 pcb with current limiting to drive 2N3055 and keep the current limiting ability?

    b to output lm317 pcb +
    c to + on bridge
    e to 0.1 ohm and add as much as needed, in this case 4 x 2N3055.

    I know this works for a variable psu I already build one. The pcb did not have current limiting only voltage regulation wich works perfect. But this time I would like the ability to limit current as well..
  2. BobK


    Jan 5, 2010
    It might work, but then you will have added additional current capability that would immediately be shut down by the current limiting.

  3. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    I doubt this is possible without using extensive additional electronics. Have a look at the LM317 datasheet, especially the functional block diagram in chapter 7.2. The current limiting circuit within the LM317 measures the output current as indicated by a resistor between the emitter of the power transistor and the output pin. Any current flowing through an external power transistor will not be effective in the curent limiting circuit of the LM317.

    What's the use of such a circuit anyway? An external power transistor (or transistors) is used to boost the output current capability of the regulator. It would be be against this intention if you limit the current to the LM317's range.
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