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LDO replacement for 7805?

Discussion in 'Datasheets, Manuals or Parts' started by Krumlink, Sep 5, 2007.

  1. Krumlink

    Krumlink New Member

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    I am looking for a replacement for the crappy 7805. For my Binary clock, I am using the 780-05 (the 1.5amp), and it craps out when the voltage reaches about 7volts and I require a extremely smooth voltage because I am using the LS series. It can power my cheapo leds. I am looking for a pin compatable (same pinout) and hookup as the 7805, that has a input voltage at least 6volts. So it will start to fail me at 6 volt input. I am using rechargeable batteries, so that can be pesky. THANKS!

    7805!!!!!!!!!!!!!!!! WOOT SN7400!!!!!!!!!!!!!!!!!!!!!!!!!

    (just some randomness there)
     
  2. Krumlink

    Krumlink New Member

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    I also would rather it be TI part. I love Texas instruments, they are nice to me. All their chips are good.

    I need about 750ma or more. I also need 5 volt. THANKS
     
  3. Krumlink

    Krumlink New Member

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  4. dave

    Dave New Member

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  5. kchriste

    kchriste New Member Forum Supporter

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    LM2937 from National will give 500ma at 5V.
    The LM2940-50IKCSE3 from Ti will give 1A at 5V
    Both are low drop out devices and are pin compatible with the 7805
     
  6. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Many low dropout regulators must have a 10uF to 100uF capacitor on their output to ground or they oscillate badly.
    Some oscillate if the capacitor has a low ESR and others oscillate if the capacitor has a high ESR.
     
  7. Krumlink

    Krumlink New Member

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    I stuck lots of caps on it to smooth out the voltage since I was dealing with the LS series.
     
  8. Krumlink

    Krumlink New Member

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    I got my samples today (one of each, 3 total) and I am going to test them out.

    :)
     
  9. Krumlink

    Krumlink New Member

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    I replaced the 7805 with the new and improved 780M05 Low Dropout regulator. I got it to put out a decent 5v output (4.98 if you want to get technical) when the voltage hit its roof, of about 6.5 volts. ME HAPPY. The binary clock will run much longer with it on there. about how many mA does a average (any/most) TTL LS series chip use? around 20 ma?

    I am using 21 LEDS at 8ma

    8*21=168ma
    10ttl chips*n(ma use)=x
     
  10. audioguru

    audioguru Well-Known Member Most Helpful Member

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    TTL LS uses a lot of current. You should have used Cmos because it uses almost no current.

    An LED display also uses a lot of current. An LCD uses a very low current but it needs to be lighted when it is dark.
     
  11. whiz115

    whiz115 Member

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    sorry for the offtopic but why does TI gives freely all these stuff to everyone that states that studies electronics or works for a company?! :rolleyes:
    is it really better advertasing for them?! the transportation costs must be
    huge.. with FedEX and UPS...
     
  12. Krumlink

    Krumlink New Member

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    I do study electronics! Im a student in highschool, and they order free samples all the time! I only ordered 1 of 3. Please refrain from making this thread another flame war.

    Audioguru, do you think that 750ma is enough for 10 TTL chips and 22 LEDs at 8ma?

    I couldnt find compliants for the LS series chips that I was using, but if so, How do I pull more ma out?
     
  13. Krumlink

    Krumlink New Member

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    Besides a Switching Regulator? What about in parallel or whatever. I forgot how it goes.
     
  14. audioguru

    audioguru Well-Known Member Most Helpful Member

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    10 LS-TTL chips at maybe 30mA each plus 22 LEDs at only 8 mA each is a total of 476mA. A regulator in a TO-220 case and without a heatsink will be very hot at 2W.
     
  15. Krumlink

    Krumlink New Member

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    It is a D2PAK with a max output of 750ma. If I put them in parallel dont they disapate the heat through them?
     
  16. whiz115

    whiz115 Member

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    it was just a question my friend...i'm not offending or doubting anybody. :)
     
  17. Hero999

    Hero999 Banned

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    That's alright, he's just a bit sensitive because he's already been involved in a flame war about free samples.
     
  18. Krumlink

    Krumlink New Member

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    Exactly, and it was 6 pages long...

    Now back on topic!!!!!!!!!!!!! (Or I will be mad :mad:)

    So do Parallel Regulators Disapate the heat formed by sharing it through them?

    If so, my D2PAKs (2 of them) will be sharing the 2W of heat by giving 1W of heat through one, and 1W of heat through the other right?
     
  19. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Probably not (at least not well), one will hog most of the current, get red hot and shut down, the second will then get red hot and shut down as well. Could be an interesting low speed oscillator design?.
     
  20. Krumlink

    Krumlink New Member

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    So what should I do to get the heats out of it?
     
  21. audioguru

    audioguru Well-Known Member Most Helpful Member

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    You add a heatsink to a regulator to cool it.
     

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