PT4115 Led diver

Discussion in 'The Projects Forum' started by LauraB, Feb 1, 2014.

  1. LauraB

    Thread Starter Member

    Dec 15, 2011
    43
    0
    Hello
    I built this circuit:


    http://www.laro.com.pl/pdf/pt4115.pdf

    I use:
    Led3W I~700mA
    100uF capasitor low ESR
    Schottky SS16
    Rs 0.13Ω
    coil 100uH
    I dont use these four diodes for the bridge, because I use a DC power supply.
    For dimming I used mC and a function generator. As far as I understand if I just leave this pin, it should be always on. Right?
    I lost a few circuits, because it makes a short between GND and SW. The diode just blinks and thats it.
    What can be wrong? A component I use? Or smt is wrong in my circuit?
     
  2. TANDBERGEREN

    Member

    Jan 20, 2014
    74
    4
    What is Your input DC voltage?
    And beware of the polarity.
     
  3. paulktreg

    Distinguished Member

    Jun 2, 2008
    612
    120
    You shouldn't just leave the DIM pin floating. Connect it to +ve rail. Then what happens?
     
  4. LauraB

    Thread Starter Member

    Dec 15, 2011
    43
    0
    My DC input is lab power supply. max 1.5A, 24V. I set it to 12V normally. And about 700mA.
    If I conect Dim to +5V it does the same... In the datasheet it's written: "The DIM pin is pulled up to the internal regulator (5V)
    by a 200KΩ resistor." So I should be able to leave it floating?

    I tried some different things and sometimes Led was lighting, but the regulator wasn't working. It's hard to test it, because every time I need to remove and solder another smd circuit. I already lost about 10-12...

    And a polarity; I connect Led's minus to the coil and plus to the resistor. The schottky diode's "line" to Vin. Is this ok?
     
    Last edited: Feb 1, 2014
  5. paulktreg

    Distinguished Member

    Jun 2, 2008
    612
    120
    You mention you set your power supply to about 700mA. Why?

    If there's nothing wrong with your build this shouldn't matter. You aren't hitting the current limit on your power supply are you? The LED current is approximately 700mA, it could be more?
     
  6. LauraB

    Thread Starter Member

    Dec 15, 2011
    43
    0
    Yes, thats true. I set 700mA for testing. Before I was trying 1A. I dont want to destroy the Led during the tests. Is that a problem? If I set too low current?
     
  7. paulktreg

    Distinguished Member

    Jun 2, 2008
    612
    120
    If your power supply hits its current limit it may drop the voltage.
     
  8. LauraB

    Thread Starter Member

    Dec 15, 2011
    43
    0
    well, I don't think it hits the limit. I has a display with a voltage and current so I can always see.
     
  9. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    using current regulated power supply with switching circuit- it could not get much worse.

    It can not work correctly, you need to remove the limit.
     
  10. LauraB

    Thread Starter Member

    Dec 15, 2011
    43
    0
    Ok. I will do that. Can I use another lab supply, but this one has no current regulation(Only voltage)?. It has max 5A. But in the other hand, if this won't work... my led will be destroyed. Am I right?
    I used before rectified 15V 800mA and I think there was a problem as well. Anyway, I will try. Could you tell me why I can't use a current regulated power supply with switching circuits?
     
  11. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    What do you mean the LED blinks? At what rate? Are you using the dim pin yet?

    I built the attached pt41115 supply some time back and it seems to work fine. I left the dim pin float.
     
    Last edited: Feb 1, 2014
  12. LauraB

    Thread Starter Member

    Dec 15, 2011
    43
    0
    I mean it flashes for a sec and it stops for good. At 12V 0.7mA-0.8mA. I tried to use dim pin but it was the same. Tomorrow I will rebuild the circuit with a different dc supply.
    In the schematic you attached there is a capacitor with plus connected to the GND?
     
  13. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    There is a 10uf to ground if that is what you mean. It is the only cap on the board.
     
  14. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    Where did you get the pt4115? I bought mine from eBay then later got an email from eBay saying the part was a bogus part but everything I seem to see they work fine.
     
  15. LauraB

    Thread Starter Member

    Dec 15, 2011
    43
    0
    I got mine from two different shops.
    But that capacitor is reversed... Plus goes to Gnd and minus to Vin. Is that ok?
     
  16. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    Typo. Thanks for pointing it out. Obviously I installed it right on the board. :) I will correct.
     
  17. LauraB

    Thread Starter Member

    Dec 15, 2011
    43
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    No problem Spinnaker.
    I connected 120V max 5A power supply. The circuit is burning, I can see the smoke. The led lights. But i haven't measure the current, cuz anyway it's burning. ehh
     
  18. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    120V ac or dc?

    Seems awfully high either way. I will try and check my datasheet but have to run right now.
     
  19. LauraB

    Thread Starter Member

    Dec 15, 2011
    43
    0
    I'm sorry. I meant 12V DC. Sorry for the misspell. Maybe it's because a schottky diode?
     
  20. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    I assume the chip is SMD? As I recall it is only available in SMD. Did you mix in through hole components like I did? If so are you certain you have everything connected correctly? I know I had to think about how to orient the chip in relation to the components on the other side of the board.
     
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