Lm723 transistor help

Discussion in 'The Projects Forum' started by HomeNucleonics, Apr 26, 2012.

  1. HomeNucleonics

    Thread Starter New Member

    Apr 26, 2012
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    Being new at this, I am attempting to set up an adjustable voltage regulator.
    Following figure 1 of the lm723 datasheet, I have a 5volt output from an input of ~16.3VDC after rectifier, Trying to up the amperage after before figuring out how to even make it adjustable, but I've been unable to get anywhere. My output goal was to be around 1A with adjusting the output between 4V-5V. Hooked the Vout to B and 16.3 Input to collecter. Is the problem that i dont have load impedance or just a bad setup?
    [​IMG]
     
  2. wayneh

    Expert

    Sep 9, 2010
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    Hmmm, whatever image you posted isn't working. Are you following some other figure in the datasheet, maybe #4? This IC cannot handle the current you're looking for without an external transistor.
     
  3. HomeNucleonics

    Thread Starter New Member

    Apr 26, 2012
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    Yes thank you, I forgot to mention that after the IC i'm using a TIP120 Darlington, the Vb is the 5V from the IC Vout, and for Vc im using the 16.3V taken from after rectifier. After that I wanted to implement the 5k pot is have,I guess in series with another resistor, Unfortunately I'm getting no good results.
     
  4. HomeNucleonics

    Thread Starter New Member

    Apr 26, 2012
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    I'm listing the TIP120 and 5k pot because these are what is available to me at the moment, as well as a multitude of resistors. I already have the LM723 set up to figure 1, so help with a configuration to increase current and develop adjustable output voltage would be greatly appreciated.
    http://www.dz863.com/pinout-813812763-LM723/
     
    Last edited: Apr 27, 2012
  5. t06afre

    AAC Fanatic!

    May 11, 2009
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    Hi can we use this datasheet as a starting point. I found your link confusing http://www.ti.com/lit/ds/symlink/lm723.pdf
    Anyway in your setup you will need a good heatsink/cooling fin. If not your output transistor will get very hot and then give up.
     
  6. dataman19

    Member

    Dec 26, 2009
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  7. #12

    Expert

    Nov 30, 2010
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    Hate to be rude but, a 317 chip is very different from a 723 chip.
     
  8. HomeNucleonics

    Thread Starter New Member

    Apr 26, 2012
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    yes correct the 317 information is of litte help, I simply need to know how to up my output. Vout of regulator is 5vdc @1mA, Vcc for tip120 collector is 16.5v, and i'd like to be able to adjust the output +/- 1V @1A(have 5k pot), Im simply not sure what a workable setup is.
     
  9. #12

    Expert

    Nov 30, 2010
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    Combine figure 4 and figure 13.
     
  10. DickCappels

    Moderator

    Aug 21, 2008
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    Gosh, the LM723 is so ancient. It was wonderful for its time, but the monolithic regulators are so much better and have additional features, such as thermal shutdown. If its any help, back in 1972, we used a 2N3055 for the output transistor for positive 3 amp supplies and a MJE2930 for the output for negative 3 amp power supplies. But unless you are doing a historical re-enactment of engineering in the 1970's, please use a modern monolithic linear or switching regulator and save yourself a lot of trouble, and get a better power supply to boot.
     
  11. #12

    Expert

    Nov 30, 2010
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    The 723 has a very convenient "fold back" protection circuit. I find this to be an advantage that I often prefer. Three legged regulators are more complicated to implement as "self protecting" when external pass transistors are used because the excess current and heat during a fault condition are not inflicted on the regulator chip.

    Sometimes this is a personal preferance decision.
     
  12. t06afre

    AAC Fanatic!

    May 11, 2009
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    And the current limit can also very easy be made adjustable. Very convenient in bench supply.
     
  13. dataman19

    Member

    Dec 26, 2009
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