Hello all, is it possible to activate (LOW,HIGH) a CL2N3. Assume that the CL2N3 is powered independently (let s say 15V for 4 leds) and I have wired the PIN5 of the arduino to the middle pin of the CL2N3. So of course it does not work but maybe somebody gets a solution! thanks.
Please show your wiring diagram
That chip doesn't seem to have an enable/disable pin.
Can't use four white LEDs with that chip on a 15volt supply either, because it needs a minimum of 5volt across. Four red leds, yes.
But why do you need a CC chip like that. They are only used if you have a large supply voltage variation and absolutely must have constant LED brightness.
For what.
Leo..
I have already put this chip in my trains. It works very well. Now I would like to know if I can use the middle pin like an interruptor.
Google "CL2N3 datasheet".
You will see that the middle pin has no function.
The CL2N3 is nothing more than a variable resistor.
If you want to switch the circuit on/off, then you must add another transistor.
Leo..
Any random digital or analog pin can drive ~20mA -- enough to drive most any LED to full (nominal) brightness with the right series resistor. The series resistor for 20mA should be 50 ohms per volt to be dropped. Say a red led is 1.6V and the supply is 5V, 5V - 1.6V = 3.4V, 3.4 x 50 = 170 ohms give or take, 160 and 180 are standard values, either will work.
Use that to drive a mosfet and you can switch any current/voltage with ease.
Thanks. Indeed.
Thanks a lot.
What would be the schematic if I used a mosfet to interrupt the current?
Thanks
Sorry Im not an artist. It s working well when I make the leds blinking. Notice that I do not put resistors between the grid and pin5 of the arduino. However the transistor is heating a lot. How can I fix this issue? thanks
this is an IRF520 N
+15 should only connect to the CL2N3.
Black wire of the LEDs connects to the middle pin of the transistor.
Leo..
Hi,
This might help:
The IRF520 N is not a logic level MOSFET, so it may not be turning fully ON.
Do you have a DMM, can you measure the DRAIN to GND voltage when you have the LEDs turned ON?
Thanks.. Tom.. 
A 2N2222 with 470 ohm base resistor will do at that current (20mA).
Or a 2N2222 with base connected directly to the Uno pin,
and a 220 ohm resistor in the emitter and no CL2N3.
Leo..
hello 11,6V between the drain and GND.
I have replicated your schematic. When I put the current divider R1+R2 nothing happens. The leds are lighting shyly without blinking. When the current divider is taken off, it working and leds are blinking loud and clear but the transistor is heating too much.
The MOSFET is not being turn fully ON.
You need a Logic Level MOSFET.
Tom...
The Fritzy drawings show an Uno.
Are you using an Uno?
Did you change the layout to what I said in post#12.
In that diagram you're trying to short out the 15volt supply with the mosfet.
Post a real picture of your current setup.
Leo..
It s working. I had missed a step. So what may be the best: 2N2222? or TIP120? I am not an expert but I had to buy some what do recommend? thanks for your time
A 2N2222 is already overkill for 20mA,
Almost any transistor the size of half a grain of rice will do for that current.
A TIP120 belongs in a museum.
Leo..
Ok so can we imagine octocoupler as a switch?