Quick help with Constant Current

Hello,
I would like to build a constant current source which outputs 150-200mA and which can be controlled through arduino PWM. I have ordered a few higher constant current circuits but they're too high (500-700mA).

I tried googling for schematics, but I don't really know how to calculate the correct values and every time I see a circuit there's attached a comment about fires and failures :o

Context: RGB strip, total: 500mA draw, each color 150-200mA, driven through Arduino

"Dumb" RGB LED strips already have current limiting resistors fitted.
Just PWM the RGB connections with a logic level mosfet to ground.

If you mean someting else, give us the full picture (links, code, etc.), so we don't have to guess.
Leo..

Wawa:
"Dumb" RGB LED strips already have current limiting resistors fitted.
Just PWM the RGB connections with a logic level mosfet to ground.

If you mean someting else, give us the full picture (links, code, etc.), so we don't have to guess.
Leo..

This's what I mean, just some basic fading etc.
I don't happen to have a logic level mosfet at hand, but I do have there parts

There is only a non-logic level IRF3205 and a 2N7000 on that list.
Lots of tutorials here.
Leo..

Wawa:
There is only a non-logic level IRF3205 and a 2N7000 on that list.
Lots of tutorials here.
Leo..

Oh, okay, no way around the logic level mosfets I guess.
Does it matter which one(s) I order?

Yeah, instead of the MOSFETs I was hoping to use similar circuit with 555

Sorry for bumping, but this is not a good idea?

outro:
Sorry for bumping, but this is not a good idea?

Not on an Arduino forum.

You could use a BD135 with 220ohm base resistor instead of a mosfet,
but total LED current will be limited to about 500mA and LED string brightness won't be 100%.
Leo..