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LM338K Availability

Discussion in 'Power Electronics' started by Electromotive, May 5, 2019.

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  1. Electromotive


    Feb 14, 2018
    I am building two regulated DC power supplies for my O-Scale (2 Rail) layout per the LM138/LM338 data sheet. I have built two 1A DC supplies but they are a little anemic for this larger scale system.

    I have all the parts and components but am afraid of the e-bay LM338K's. One of the 2 is definitely a problem. I would like to purchase a minimum of 5 quantity.

    It is a 0-18VDC power supply using a 4 Amp 24V transformer. I would prefer the T0-3 K Steel package but see that most of the reputable US firms like Mouser, Digikey and Newark are either $50 each or unavailable.
    I need the 1.2V lower end limit, as 4V may already initiate the train starting.

    Also, I am not sure how to calculate the heat dissipation. My Heat sink is 2" x 3" x 4".
  2. Electromotive


    Feb 14, 2018
    I am so afraid of the various potentially knock-off manufacturers of the LM338K. I find them from $1.00 to $60 and that is bulk rate.
    Here are some of the more reasonable P/N's:
    Sh12AB (Backwards) S
    H1027 S
    9442 Philippines
    Jameco 23835
    ST Microelectronics
    Can anyone advise what a reasonable price is for an LM338K? And a possible source?

    Thanks... Tom
  3. Electromotive


    Feb 14, 2018
    Hi Ylli:

    Thank you for your kind response.
    Working with these older and often discontinued items is a little frustrating.

    Can you advise why you feel the New Egg vendor is the way to go?

    The LM338K on this web sight has the same SH12AB P/N as many on e-bay. The part is coming from Israel and the vendor ALEXNLD has a miserable track record of deliveries (>>1 month) and only rates a positive of 54% out of 892 reviews. That is a low rating and the number of reviews is rather low for an active electronics part vendor. On the other hand, New Egg puts up with him/her.

    While I thank you for your response, I don't feel real comfortable with this vendor. Maybe someone here has personal dealings with the LM338K.

    Thanks... Tom
  4. Ylli


    Jun 19, 2018
    Always had acceptable service from Newegg. Alternately, you could always go with an LM317 and an external pass transistor.
    duke37 likes this.
  5. Electromotive


    Feb 14, 2018
    Hi Again:
    After reviewing all options on LM338K non-availability or cheap knock-off's everyone is advising against due to inferior product, I have ordered LM338T's from Newark. Slightly different package but should work. And they are made by Texas Instruments at less than $2.00 each.

    Thanks to all for the help in this.

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