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Substitute transistor.

Discussion in 'General Electronics Discussion' started by sureshot, Mar 1, 2016.

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  1. sureshot


    Jul 7, 2012
    Having a look for another decent psu circuit i found this in the image below. Problem is i am having problems finding a BD131 NPN transistor.
    I was wandering if anyone can help with a substitute, thanks for reading, any help appreciated.
    Having a few ideas like the BD437 but not completely sure.

    Attached Files:

    Last edited: Mar 1, 2016
  2. davenn

    davenn Moderator

    Sep 5, 2009
    not to put you off too much, but the 723 regulator is a very old and dreadful to use regulator chip

    you would be much better going to LM338 style .... just a suggestion :)

  3. 73's de Edd

    73's de Edd

    Aug 21, 2015

    Sir Sureshot . . . . . . .

    I always used to utilize a TO-66 cased 2N3054 in those regulator strings as the first driver, and the little brother of TO-3 cased 3055's..

    The specified BD131 specs out with:

    Collector to base voltage 70V
    Max collector current 3A
    Power dissipation 11W
    Beta 40

    Here is a whole page of that 2N3054 power NPN family, plus newer / others that even excell its specs.

    I still like that LM 723, for its holding tight load to unload regulation capabilities as well as just regulating to a wide voltage input swing, plus its ADJUSTABLE foldback current limiting you see being involved on its pin 2..
    Before that "old " part, which was a many, many year industry standard for a linear supply voltage chip (or shunt also ) I even used the forerunners top hat LM304 and LM 305's.
    Before that, it was being MULTI discrete parts design.

    73's de Edd
    SOLARWIND likes this.
  4. sureshot


    Jul 7, 2012
    Thanks Davenn. I have built an lm338K and an lm338T version linear regulator supplies. I was moving towards the more challenging circuits, not just for there PCB layout but also unit constructional layout. I've never used the 723 Regulator, but though I'd give it a go.

    Retail psu's I've looked into in the past look like they use it, or a variant off it. I'm always looking for new psu circuits, so if one pops up with a different regulator or IC at the heart of it I may go with that instead.
  5. sureshot


    Jul 7, 2012
    Thank you Edd. I will have a look at your surggestion, of the 2N3054, and thanks for the link ! Always a pain in the back side when you find a circuit, only to be challenged by obsolete of hard to find parts lol.
  6. sureshot


    Jul 7, 2012
    Thanks for your help here, a bit more searching and I've managed to pin down a supplier with the BD 131 transistor, thanks again all.
  7. AnalogKid


    Jun 10, 2015
    There is nothing wrong with using another 3055 as the darlington driver.

    SOLARWIND likes this.
  8. sureshot


    Jul 7, 2012
    Yes it certainly powerful enough, it achieves the Darlington configuration, and the HFE is about there almost. But as I can get the BD131 for £0.80 its not to bad. Thank you for the tip ! Appreciated.
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