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Topic: Switching 9V power based on Arduino's 5V output (Read 3180 times) previous topic - next topic

random_vamp

I have a chandelier that I had previously build that has a number of 3x3V LED circuits running off a 9V power supply (60mA per circuit, around 800mA combined).  Now I'm looking to control the individual circuits from an Arduino, and need some advice for how best to switch the circuits.  I could just purchase a pre-built array of relays, but that seems overly costly for this purpose.  Its my understanding that I should be able to wire up an appropriate transistor to perform this switching, and I did get switching working using a 2N2222 transistor with a few different combinations of resistors.

However the problem I have is that in none of these combinations (even with the 9V power supply wired through the transistor with no resistor involved) the LEDs don't light anywhere near as brightly as when connected directly to the 9V input, presumably they're not getting the full 9V output.  I tried varying the resistor between the Arduino's 5V output and the transistor, but didn't get much improvement.

Does anyone have a suggestion on how to improve this?  Should I be using some other transistor (I know little about the options available here), or should I perhaps try getting a 12V supply to account for voltage loss over the transistor?

TerryKing

Hi,
The 2N2222 should have less than .5 v drop at 60mA. What value is the resistor from Arduino to base?  220 ohms should give you plenty of base current into the 2N2222.

What is the emitter-collector voltage when turned on??


nickgammon

Does the transistor get hot? According to my data sheet it will handle 600 mA, not 800 mA.
Please post technical questions on the forum, not by personal message. Thanks!

More info: http://www.gammon.com.au/electronics

TerryKing

@random, maybe I'm confused. You said:
Quote
has a number of 3x3V LED circuits running off a 9V power supply (60mA per circuit, around 800mA combined).  Now I'm looking to control the individual circuits from an Arduino, and need some advice for how best to switch the circuits.


Are you trying to control 60mA per transistor? or 800mA an ALL the LEDs??

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