trouble with voltage regulator

Discussion in 'General Electronics Chat' started by frankinaround, May 14, 2012.

  1. frankinaround

    Thread Starter New Member

    May 14, 2012
    15
    0
    Hi I've been building a power supply. Step down 120 60hz to 28v. Put threw bridge rectifier. Then put threw regulator. 2 1k uf capacitorsand a .1 cap are in parrallel with the input of the regulator lm317. Then 100 ohms resistor from. The output connects with a potentiometer of 5000 ohms which connects to adjust of regulator and ground. Then on the output there's a1ohm capacitor in parrallel.

    The problem is I'm trying to hit 19 volts but everytime I raise itusing potentiometer it hits 14 volts then jumps to 5volts.

    I think its most likely because I don't have a heat sink (radioshack didn't have ithad to buy from jamco). But I thought that it gets hotter when the difference from input voltage to output was higher, so it. Seemed strange to me that it would jump from the. High output to. Low output voltage.

    Any ideas as to problem ? Also I want 1.5 amps and I hink lm317 is for less anyone know a better regulator to order ?
     
  2. jwilk13

    Member

    Jun 15, 2011
    228
    12
    Can you provide a schematic?
     
  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
    969
    Mains powered circuits without a proper transformer are against the terms of this forum and should not be discussed as they can be very dangerous.
     
  4. paulktreg

    Distinguished Member

    Jun 2, 2008
    611
    120
    "Step down 120 60hz to 28v."

    Sounds like it could be a transformer to me?
     
  5. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,535
    Me too.

    Heat sinks are not optional for analog regulators like this. You can buy clip on types very cheap, but if you are going to use the full 1.5A then you might want to think over kill, like an old CPU heat sink and fan.

    This is pretty true of any linear regulator chip.

    SMPS (switching mode power supply) regulators tend to run much cooler, but they need heat sinks too. Just look at any computer power supply.

    Basic Bench Top Power Supplies

    Bill's Index
     
  6. frankinaround

    Thread Starter New Member

    May 14, 2012
    15
    0
    Yeah its a transformer. Ill post. A schematic tonight. Yeah I knoe needs heasink. It gets very hot fast. But could that cause the problem I'm having ?
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    Yes. Most modern IC regulator (and this one is quite old) have some very good protections built in. Even so, you may have damaged this chip.

    They are quite complex IC's when it comes down to it.

    If you look at the data sheet, they have ways to increase the current quite a bit, but the over current protections are by passed in the process. At this point, the transistors are there to protect the fuses (a very old joke).

    Suggestion, read the links. Schematics are included, as well as some sound advice.
     
  8. nagaronlinepowers

    New Member

    May 21, 2012
    1
    0
    Before we get to the solution of power problems, we must first understand the five major power problems and what causes them.
     
  9. Wendy

    Moderator

    Mar 24, 2008
    20,765
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    Really? Care to elaborate?
     
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