Transistor Substitute, LED Amplifier

Discussion in 'The Projects Forum' started by Leccy-Lee, Aug 22, 2008.

  1. Leccy-Lee

    Thread Starter Member

    Aug 2, 2008
    22
    1
    I cant find a transistor i have in a schematic, i found the datasheet and tried to pick a common substitute but confused by the datasheets data. Especially when the ratings all seem to be minus numbers? Such as IC = -1A ?

    The transistor i am trying to substitute is a 2SA0683 its PNP nas only being used a simple amplifier for hi-power LEDS. My control puts out 20mA per LED and i need to up it to 350mA. I have all the schematic and plans i just cant find these actual transistors.

    Thanks, apologises for being a dumb-ass!
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    2SA0683 is an Asian number. Panasonic is one manufacturer of that device.
    Well, take a look at a BC327. Not as high rated, but will carry more current than your circuit requires. PN2907, TN2905 would also be in the ballpark.

    Don't let the negative numbers throw you; that's just because it's a PNP rather than an NPN. You'll run into the same kind of thing looking at P-ch MOSFETS vs N-ch MOSFETS.

    Why don't you post your circuit, so we can have a look-see?
     
  3. Leccy-Lee

    Thread Starter Member

    Aug 2, 2008
    22
    1
    Thankyou Sgt, it was the negative numbers that totally threw me, else i think i could have figured it out eventually. I will sort out a circuit later, its one of the internet anyhow, not brave enough yet to work out my own designs.

    Thanks, i will grab some BC327's later :) Although out of interest, where i am i going wrong in selection? I was looking at IC in my local suppliers catalogue and it shows BC327 as 100mA, so i figured that was too small? So which figures i am getting wrong.
     
    Last edited: Aug 22, 2008
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I'm looking at Fairchild Semiconductor's sheet for the BC327/BC328.
    Under Absolute Maximum:
    Ic = -800mA
    Your supplier probably listed it with a conservative rating; the gain starts to roll off after Ic=100mA
    The transistor will need to be in saturation to get full current. Figure on a base current around 1/30th of your load, or roughly 12mA. Size your base resistor accordingly.
     
  5. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    There are lots of variants of the BC327/337 complementary pairs, but none were ever rated at only 100mA.

    It's possible that there was a misprint the also popular BC557 series comes in 100mA versions.

    It's also possible you misread the specs. Take another look. The gain (beta or Hfe) is quoted at a typical collector current. 100mA would be appropriate for a BC327. Perhaps you saw this column?

    You can also add BC640 and TIPP32 to your list of suitable substitutes. These both have 1000mA or greater capacity.

    Be careful to check the lead configuration as there are many variations in the TO92 package your transistors come in.
     
    Last edited: Aug 23, 2008
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