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LM2596 troubles

  1. Mar 29, 2017 #1
    Hi,

    I have been using lm2596 recently for my project and encountered weird issue with it.
    I am using it to step down the voltage from my bike dynamo which is 16v down to 5V for my front and back tail lights. But it is getting burned I guess when I ride the bike and I had 3 times changed the lm2596 IC. Therefore, I dont know what is wrong with it. when it crashed, there was short circuit between in and out pin. Here is my schematics. Please let me know your opinions and give advice.

    upload_2017-3-28_23-58-1.png
     
  2. jcsd
  3. Mar 29, 2017 #2
    - Is that dynamo reliable? Without voltage peaks/sparks? DC?
    - I could not find what this chip does when Vin < Vout. The datasheet suggests some external circuitry for undervoltage lockout, this might suggest that it has no protection for it?
     
  4. Mar 29, 2017 #3

    Baluncore

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    How certain are you that the dynamo produces +DC and not AC or –DC ?
    The LM2596 should survive 40 volts input.
    Maybe install a power diode between the generator and the reservoir capacitor, C1. Monitor that capacitor voltage to identify the maximum input voltage to the LM2596.
     
  5. Mar 29, 2017 #4

    jim hardy

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    Bike? As in motorcycle?
    Dynamo? As in brushed DC generator? What is the nature of its voltage regulator?
    If turning off the ignition key disconnects your dynamo from your battery (as on some old dynamo equipped Harleys) you can expect a very large voltage transient at the dynamo when you switch off the ignition. Try a big rectifieir across input to your 2956, cathode to positive .

    If instead your "dynamo" is the rectified 3 phase permanent magnet alternator typical on modern bikes, be aware that in absence of voltage regulator they can put out 60 volts at high RPM when electrical demand is low.

    That's two possibilities for you to investigate.
     
    Last edited: Mar 29, 2017
  6. Mar 29, 2017 #5
    Yes , dynamo is reliable. And I am using bridge rectifier with filtering capacitor and lm2596 input capacitor also helps to reduce/eliminate the picks.
     
  7. Mar 29, 2017 #6
    Hi, I am certain that it produces +Dc since i am using bridge rectifier and capacitor. Ok I will try to put diode.
     
  8. Mar 29, 2017 #7
    Is there any way to make a constant current source for 5v 1.5 A regardless of voltage change in dynamo?
     
  9. Mar 29, 2017 #8

    Baluncore

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    Can you give the make, model and year of your bike or the generator?
    Do you know if it is a generator or an alternator?
     
  10. Mar 29, 2017 #9

    jim hardy

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    sophiecentaur taught me that some little bicycle lighting generators are nothing more than a permanent magnet alternator, sans regulator or controls.
    That of course would produce AC . Filtering would be the thermal lag of incandescent head and tail lamps.
    We've no idea what he has.

    There's no bridge rectifier shown on your drawing. Would you add it, and values of your components?



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