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solar lamp circuit without transistors

Discussion in 'General Electronics Discussion' started by marcia, Nov 15, 2010.

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  1. marcia

    marcia

    4
    0
    Nov 15, 2010
    Hello,

    I've disarmed a garden solar light and need to reconstruct its circuit, but I can't figure it out, because it has no transistors.
    I've searched the internet and haven't found any circuit without transistors.

    Here are the parts :
    - one diode
    - one resistor, apparently 12 Kohm
    - one inductor, apparently 100 µH
    - one capacitor 10 µF
    and of course one led (orange) And that's all.

    It's on a board where connections are not visible, so how is everything connected?
    Thanks for any reply
     
  2. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    All those parts point in one direction only; there is a transistor, or rather an IC somewhere. Can you provide a picture of the board?
     
  3. marcia

    marcia

    4
    0
    Nov 15, 2010
    No transistors

    That's what boggles me, there are no transistors. Here is a (bad) picture of the board and I can dismantle another solar light (same model) and photograph it still armed if you think the transistors might be hidden elsewhere?
    :confused:
    Thank for your interest.
     

    Attached Files:

  4. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    The first picture is not too bad (hehe, it even shows your little helper), but how about the underside of the board, could there be anything there?
     
  5. marcia

    marcia

    4
    0
    Nov 15, 2010
    the back of the board

    On the back of the board, there is a black blob. Could an ic be hidden underneath?
    I thought it was meant to secure connections under stress.
    The scratch (on the right) is an attempt to find a connecting thread to one end of the resistor, to no avail.
     

    Attached Files:

  6. Laplace

    Laplace

    1,252
    184
    Apr 4, 2010
    @marcia "It's on a board where connections are not visible, so how is everything connected?"

    Even with the poor quality of the photos it seems obvious that the connections are visible. Just assume that anything soldered to a contiguous patch of copper foil is all connected together.
     
  7. marcia

    marcia

    4
    0
    Nov 15, 2010
    mysterious connections

    Yes, the photos are very bad, I apologize for it.
    Some connections are visible, there are tiny paths connecting :
    - the positive lead of the led to the positive pin of the capacitor
    - the negative lead of the led to the black blob
    - another path goes from the positive lead of the led to the edge of the board
    - the pin just on the right of the blob and connected to it is the inductor, the other side is connected to the positive side of the battery and the positive of the solar cell.
    So, there are some clues after all.
    But the resistor has no paths from either side, so I scratched the green coat and underneath there seems to be copper. So, is the resistor connected to everything else ? Or should I scratch the whole board to see if there are sort of barriers ?
    I'm a newbie in electronics, as you surely have surmised, and this circuit of a mass produced solar garden light with no transistors and no visible ic is really difficult to figure out, for me, a riddle. I searched the internet for hours and haven't come with anything similar. There are always either transistors or ic, to turn on the led at nightfall (which this lamp does).
    So, I have another question : if I buy the same components and experiment with them on a breadboard, should I buy different sets as I can damage some components if I connect them wrong?
    And would it be a total waste of time as it is not possible to make a solar light circuit without transistor or ic ? Any advice?
    Thanks
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,418
    2,788
    Jan 21, 2010
    Google "Printed Circuit Board" to learn about them (you're looking at one)

    Under the black blob is a device that you'll probably never be able to determine.

    Google "LED Solar gardel light schematic" for some circuits that you have some hope of understanding and/or replicating.

    Without a transistor (or some active component) you will not be able to replicate the functionality in any meaningful way.
     
  9. Laplace

    Laplace

    1,252
    184
    Apr 4, 2010
    From what I can tell, the "tiny paths" are areas where the copper foil has been etched away thereby leaving larger patches of isolated copper foil that connects the components soldered to it. The black blob must be a surface mount device (SMD), possibly a transistor. If you have access to a Xerox machine, one technique I use is to make an enlarged copy of the foil side in photo mode, then identify the solder points and draw the components on the copy between the solder points. That makes it much easier to construct the schematic of the circuit. Once you have a full schematic it may even be possible to figure out what that blob is supposed to be.
     
  10. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Your camera focused on the reflection of the lamp rather than the board.
    Yes, underneath the black epoxy blob is an IC (it's a bare chip with those delicate bond wires on). In my experience these blobs makes for a very unreliable product.
    It's not possible to remove the epoxy w/o destroying the IC completely btw.. No repairs or replacements can be done, not even with SMD components.
    Underneath the elevated light-green areas is copper foil that of course conducts and connects the solder points to each other. Another name for it is track.
    Underneath the sunken darker-green areas is absence of copper (or bare circuit board if you like). Of course these areas insulate the tracks from each other.
     
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