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Pot problem with a Lm337

Discussion in 'General Electronics Chat' started by be80be, Feb 19, 2018.

  1. be80be

    Thread Starter AAC Fanatic!

    Jul 5, 2008
    What size of pot do I need there I just killed 2 1/2 watts when I went to below 8 volts
    Screenshot from 2018-02-19 02-08-07.png
  2. be80be

    Thread Starter AAC Fanatic!

    Jul 5, 2008
    I figured it out i used wrong pinout on the lm337
    wayneh likes this.
  3. dendad

    Distinguished Member

    Feb 20, 2016
    Yes, I've been caught with that too!
    be80be likes this.
  4. Bordodynov

    Well-Known Member

    May 20, 2015
  5. ebp

    Well-Known Member

    Feb 8, 2018
    For a dual supply like that where the load is not well known, it is generally a good idea to put a diode (1N400x are usually OK) across (i.e. to ground) each output to protect the regulator from wrong-polarity bias on its output. Some regulators won't start up properly if their output is pulled more than slightly to the "wrong" side of ground.
    An inverse diode from output to input of each reg will also protect the regulator in the even that the input supply drops while something holds up the output voltage (e.g. battery) and the circuit design is such that reverse current could flow through the regulator. Reverse current can damage the reg. Bench supplies suffer all sorts of indignities.

    I haven't used one in many years, but I have a vague, possibly wrong recollection that the 337 should have more than 1 µF at its output for good performance. Some negative regs are a bit on the slow side so more capacitance helps with regulation with fast-changing loads.