Converting a 5v transistor switch circuit to work with a 3.3v Arduino

Using Arduino General Electronics
1

Hello,

I have a transistor switch circuit driving an LED light array with PWM that is working great with my 5v Arduino, and I'm not sure how to modify it to work properly with my Teensy 3.0, which is 3.3v.

The circuit is like this:
collector ----> gnd of LED array ---> LED array ---> 12V
/
PWM output ---------> 1k? resistor ----> TIP29C base

emitter ----> gnd

What value of resistor would make this circuit work as a switch with a 3.3v PWM output? It's been a couple of years since I've done these calculations...

Thanks to anyone that can help!

Drew

2

Also, here's a post I made that might explain the circuit better LEDs dimmer when running through transistor - General Electronics - Arduino Forum.

3

You haven't defined "an LED array".
Can it be assumed that some form of current limiting (resistors) is included?

If so, you'd use the circuit on the right (common emitter).
A TIP29 is a power transistor, it does not have a lot of gain.
Without knowing what kind of current this "LED array" requires, it may be that you cannot get enough base current to get that thing going.
For "R1", in the circuit on the right, use 100?.

Perhaps you could provide more details.

4

Sorry, my engineering knowledge failed me there.

LED array is the following:

12V ----> 150? resistor ---> LED ---> LED ---> LED ---> transistor collector
--> 150? resistor ---> LED ---> LED ---> LED --/

5

Looks like "80 mA".

Try the 100?, then try 220?, then try 470?.
What do you have so far?

6

But those 150? resistors should be > 330?

7

470? did it! Thanks!

8