Replacement transistors

Discussion in 'The Projects Forum' started by snav, Jan 18, 2014.

  1. snav

    Thread Starter Active Member

    Aug 1, 2011
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    I have A 12v drop light that quit and I can't find the transistor listed anywhere.
    It's an H8823DTAP. It ran for about 100hrs total.

    I did notice it wouldn't start a different(color temp) lamp so I don't know what is special about the lamp. I would upgrade to heavier duty transistors if anyone could look at it and make a recommendation.
     
  2. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Thanks for posting the excellent photos. The only thing missing would be a good photo of the front of a transistor, showing all the markings.

    Sorry my lookup books do not list that transistor part number.

    The circuit is extremely minimalist and is a push-pull symmetrical inverter driver. The black wire is +12v and the white wire is GND.

    The circuit configuration shows identical NPN transistors or NFETs, but based on the low value of the two base drive resistors (560 ohm) they are NPN transistors.

    I've fixed a lot of push pull 12v Fluoro inverters, usually these days they use NFETs about 30v and 7A rated. Older drivers using NPNs like yours usually use NPNs rated for about 60v and 3-4A.

    If you want some really nice NPNs try 2SC2335, they have decent gain and excellent specs for inverters, rated at; 500v 7A 40W.

    They are a pin for pin replacement of your NPNs which are a standard pinout of BCE (B is the side with the resistor). Ont he 2SC2335 B is the left pin, looking from the front (BCE).

    Just be aware that in about 30% of cases a blown FET or transistor means the SMPS transformer is dead with a shoted turn. However the short running life of yours likely indicates it just overheated and cooked the transistor(s).

    The two resistors should be replaced too, with at least 1/2W parts.
     
  3. snav

    Thread Starter Active Member

    Aug 1, 2011
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    10
    I drew the circuit out but can't scan. Here's photo of blown/other side. the blown one is more readable. I have read that the 12v version of flourescent lamps don't have built in starters so that's maybe why it wouldn't start/run a warmer color lamp. I ran the light for 60hrs after trying the non 12v lamp but maybe it made it fail.
     
  4. snav

    Thread Starter Active Member

    Aug 1, 2011
    100
    10
    Would FET be better? I have some irf510 on hand.
     
  5. snav

    Thread Starter Active Member

    Aug 1, 2011
    100
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    The way I drew it out is the emmiters are grounded, the collector(s) are fed from L1 through the center tap and secondary taps. C1(.22@63v) connects these together with base driven by winding/resistor connection. Not sure if base or collector are on ends of winding and the other is on taps. Output is through c2(.002@1250v) to grounded secondary.
     
  6. Chippie

    New Member

    Jan 17, 2014
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    They look like 2SD882 devices to me....
     
  7. inwo

    Well-Known Member

    Nov 7, 2013
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    Anything like this?
     
  8. tindel

    Active Member

    Sep 16, 2012
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    With only 100hrs on it... can you take it back to where you bought it? The thing is JUNK!
     
  9. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    You seem to know how to take close-up photos. Snap one of your drawing if you don't have a scanner.
     
  10. snav

    Thread Starter Active Member

    Aug 1, 2011
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    Well it's a sketch so no comments, and my camera seemed to have contrast issues but here it is.
     
  11. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Agreed! :)
    2SD882 = NPN, low sat, 40v 3A 10W, TO126 size pack, ECB looking at the front writing.
    (The 2SC2335 is pin compatible, just reverse the body).

    Nope, that is a multivibrator push-pull driver. This one is simpler and has the two Bases driven from two transformer windings.

    To Snav; yep that circuit looks good apart from the two Base feedback windings would be referenced to ground or direct to the +ve (centre pin).

    You just need two new transistors, two new resistors, and it should be running. Sometimes the output cap will fail, so it might be worth replacing that (use a 630v rated poly cap).

    Definitely use better transistors, those 40v 2SD882 are barely up to the task.
     
  12. snav

    Thread Starter Active Member

    Aug 1, 2011
    100
    10
    The cap that ties the two collectors together measures .156uf on both my fluke and my old vacuum tube cap tester. It's a little bit overkill but I have a nice 400v rated film type in my junk box that measures .226. Not sure how important that value is.
     
  13. alexfreed

    Member

    Oct 8, 2012
    72
    10
    The cap between the collectors sets the resonant frequency - probably better to leave its value alone.

    As for the transistors you could probably try dirt cheap and common BD139.
     
  14. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Sure the polarities are right on the transistors? The circuit looks a lot like the inverter on my CD ignition which uses PNPs:
     
  15. snav

    Thread Starter Active Member

    Aug 1, 2011
    100
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    the layout is in the pics and people have IDd the transistors as NPN. That part is an ECB pinout.
     
  16. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Agreed on not changing that cap, plus that small cap on the primary doesn't fail.

    The larger HV poly cap on the secondary can fail and cause bad ignition of the tube and/or overheating of the transistors.

    I disagree strongly on using BD139 replacements! It is only 1.5A rated and has poor gain and poor saturation voltage so it will cook and is a poor choice for inverters.

    This inverter is rated 13W and runs about 70% efficiency so the trannies will be switching around 1.5A to 2.2A every cycle (as inductor peak current is higher than average on-state current).

    The original low-sat 2SD882 was barely up to it, a BD139 will be lucky to last a couple of hours. The 5 amp 2SC2335 I recommended is a superb choice for low power inverters as a general replacement. It's fast, has good gain, low sat, and is a slightly larger package with a metal tab so it will run a much cooler die temp. :)
     
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