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Topic: Using BC327 instead of BC337 but not working as expected? (Read 8 times) previous topic - next topic

dtokez

Hi all.

I am trying to control some LED downlighters (3w). I had the circuit working from arduino PWM pins with BC337's nicely, but I have now got hold of some TLC5940 IC's so want to use them. Because they sink current I had to get some BC327's instead.

Not sure why but the BC327's are getting very hot? I'm switching about 350mA through them (same load as BC337's) and have the base connected through a 1k resistor to one of the pins on the TLC5940  (the TLC is set as constant current drivers 20mA on all pins). I have also tried other values to current limit from the base, 1K does not seem to be fully saturating the transistor, and lower than 1k the things gets super hot!

I hooked up the same circuit using both the BC337 & 327, obviously driving the base high or low according to the transistor, and same behavior, the 327 getting very hot and the 337 staying cool?

Really confused about this at the moment!

Runaway Pancake

Whereas you were using NPN (337), you're using PNP (327) instead?

Schematic.
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dtokez

Yes that's right, I was doing digital and analog writes from the arduino pins using the NPN's and it was working OK, the TLC5940 works fine too when sinking 20mA from LED's directly.

Attached is a schematic of how I have connected it


be80be


Runaway Pancake

Right.
And.. does the TLC output ever get up to 12V?
"Hello, I must be going..."
"You gotta fight -- for your right -- to party!"
Don't react - Read.
"Who is like unto the beast? who is able to make war with him?"

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