L78L33 AND L78L05 Issues

Discussion in 'General Electronics Chat' started by ut1205, Mar 29, 2014.

  1. ut1205

    Thread Starter New Member

    Mar 20, 2014
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    I placed an order for parts a couple of weeks ago and ordered a few L78L33's and L78L05's for times when current demand was low and space was tight.

    I have used the LM78XX series in the past with no issues but I am having a problem with these.

    Data sheet and wiring diagram are here:

    http://www.taydaelectronics.com/datasheets/A-492.pdf

    I have wired them as per diagram except in place of the .33uf on the "IN" side I have used a .47uf. I am using an led pulling about 15 ma for a load.
    The power supply is set at 6 vdc.

    On the 3.3 (and I tried three of them) I am getting 4.6 volts, 5.2 volts and 5.4 volts. Also within a matter of seconds it gets blistering hot.

    On the L78L05 with the same setup except power supply set at 9 vdc I am getting 8.4 volts.

    Checked with a second VOM and readings the same.

    Am I doing something wrong?
     
  2. #12

    Expert

    Nov 30, 2010
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    Apparently you are, unless you got counterfeit parts. Show your schematic. We can't tell how you wired these up from the datasheet.
     
  3. ut1205

    Thread Starter New Member

    Mar 20, 2014
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    On the third page of the data sheet (Test Circuit) it shows it. Basically, "IN" to 6 vdc power supply and thru .47uf electrolytic cap to ground. Center pin to ground. "OUT" to load and thru .1uf electrolytic cap to ground.

    Edit: This is just on a breadboard by itself. It is not installed in any other circuit.
     
    Last edited: Mar 29, 2014
  4. #12

    Expert

    Nov 30, 2010
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    The schematic on page 3 neglects to show the minimum load to keep the output voltage down to what it's supposed to be.
    See page 5, quiescent current, 6 ma. That means, "minimum load current".
     
  5. k7elp60

    Senior Member

    Nov 4, 2008
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    Are you connecting them wrong. The pin connections for the t092 are shown as the bottom pins, the reverse of the top view.
     
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  6. ut1205

    Thread Starter New Member

    Mar 20, 2014
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    Without changing anything, I just plugged in an LM 7805 with the ps at 9 volts and got 5.01 volts, and an LM 7809 with the ps set at 12 volts and got 8.99 volts. I would think that 15 to 20 percent of the rated capacity would be enough to stabilize the output voltage of the L78L33 but I might be wrong. The intense heat leads me to believe that there is something wrong inside the chip. I'm going with defective parts!

    Thanks for the reply.
     
  7. ut1205

    Thread Starter New Member

    Mar 20, 2014
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    No, that's the first thing I checked. Looking at the flat side left pin in, righ pin out, plus the LM78XX's are working fine without changing anything.
     
  8. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    As Inigo Montoya said "you keep using that word. I do not think it means what you think it means."

    The quiescent current is the current from Vin to GND when Iout is zero.

    @ut1205: What package are you using? IF it is the TO-92, do you think the figure shows TOP or BOTTOM view?
     
  9. ut1205

    Thread Starter New Member

    Mar 20, 2014
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    It's the T0-92 package. I see the concern as to whether that is the top or bottom view. I'm looking at that as the top view. The way I have it on the breadboard is if you held it with the flat part point toward you and the three pins were pointed at the floor then the "In" would be on your left and the "Out" on your right. That would also match the pins of the LM78XX series.

    Do you think it is the bottom view with the "Out" on the left side?
     
  10. #12

    Expert

    Nov 30, 2010
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    You certainly caught me looking the wrong way. In my past experience, the adjust pin has only some microamps coming out. I guess fixed regulators don't have a minimum load.
     
  11. ut1205

    Thread Starter New Member

    Mar 20, 2014
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    I just went back to the bench and flipped them around. Got 3.37 on the 3.3 volt and 5.1 on the 5 volt. If the flat part is facing you then "Out" is on the left. The picture shows the bottom view and the hookup is opposite that of the LM78XX series. My mistake.
     
    Last edited: Mar 29, 2014
  12. k7elp60

    Senior Member

    Nov 4, 2008
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    That is what I was trying to tell you. This is from the data sheet:
    Figure 1. Pin Connection
    (top view, bottom view for TO-92.
    don't feel bad I have made the same mistake.
     
  13. kaspesla

    New Member

    Aug 4, 2014
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    Hah! I just made the exact same mistake. Voltage wrong, chip blisteringly hot. What on earth?
    Thanks for this thread!!
     
  14. MrChips

    Moderator

    Oct 2, 2009
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    Don't go by the pinouts of a 78xx.

    Every 3-pin device could be different.

    Will get you every time.
     
  15. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    The T092 regulators are always backwards compared to the TO220 regulators.
     
  16. MrChips

    Moderator

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    I have seen TO220 regulators such as LT1086 with

    1 - GND
    2 - VOUT
    3 - VIN
     
  17. kaspesla

    New Member

    Aug 4, 2014
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    I'm a newbie, but in this case the data sheet said above the diagram:

    Figure 3: Pin Connection (top view, bottom view for TO-92)

    And I simply stopped reading at the comma... ;)
     
  18. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Yeah sorry MrChips I was referring to 780x vs 78L0x, the TO92 'L' version of the regulator always has reversed pinout.
     
  19. takao21203

    Distinguished Member

    Apr 28, 2012
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    Never trust a voltage regulator, always connect a LED + 2.2k resistor + measure.
     
  20. MrChips

    Moderator

    Oct 2, 2009
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    What I meant was: Always check the datasheet for correct pinout.
     
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