Lm338T use and info

Discussion in 'General Electronics Chat' started by 12189187, Jul 31, 2009.

  1. 12189187

    Thread Starter New Member

    Jul 31, 2009
    Am interested in electronic power supplies for low voltage equipment using the LM338T voltage regulator in parallel to increase current output, with variable voltages from 1.2 VDC to 37 VDC. I would like to eliminate the OP. AMP's commonly used to keep the regulators in balance, and get balance by a simpler means.
    Thanks anyone.
  2. Dave

    Retired Moderator

    Nov 17, 2003
    I've moved this to a more suitable forum and removed your e-mail address to prevent it being picked up by spammers.

  3. k7elp60

    AAC Fanatic!

    Nov 4, 2008
    I think you can connect the input terminals and the adjust terminals together. Connect a 0.1Ωor 0.2Ω resistor between the output of each regulator and a common point. From this common point to the adjust terminals connect a resistor. The value of this resistor will depend upon the minimum load current. If there is going to be a load greater than 10mA for each regulator in parallel then 120 or greater can be used. Then calculate the value of the variable resistor from the adjust terminals to ground.
    The 0.1Ω or 0.2Ωr resistors will equalize the regulators.
    The 338 needs a minimum load current of 10mA for stability. If there is going to be times when there will be no load on the power supply then the resistor between the output terminal and the adjust terminal needs to be 120Ω/# of regulators. As a result the adjustment resistor will also be smaller.
  4. 12189187

    Thread Starter New Member

    Jul 31, 2009
    Thank you K7elp60. I was going to try something like what you suggest, but will follow your scheme exactly. I am useing a 20 Amp. x 29 Vdc switching supply with a 15K mfg. filter cap. and a large ferrite torroid filter coil in series with input. I had a 16K bleeder resistor across the input terminals, but will move it to the output terminals to get the required no load current draw. Any further suggestions will be truly appreciated, and if this works right, I will be in debted to you.