Transistor Substitute, LED Amplifier

Thread Starter

Leccy-Lee

Joined Aug 2, 2008
22
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!
 

SgtWookie

Joined Jul 17, 2007
22,201
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?
 

Thread Starter

Leccy-Lee

Joined Aug 2, 2008
22
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.
 
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SgtWookie

Joined Jul 17, 2007
22,201
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.
 

studiot

Joined Nov 9, 2007
5,003
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.
 
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