Transistor choice?

Hi, I want to PWM 4 RGB LED's from the Arduino, and need help finding a transistor or something that'll work. The TIP41C's work for my small DC fans, but the Arduino apparently wouldn't be able to supply enough current to switch the bases with a 12V 1.4A load?

So basically, I am looking for a transistor I can use to PWM 12V @ 1.4A, from the Arduino's PWM output, from here: http://www.jaycar.com.au/index.asp

Anyone know if any are suitable?

Cheers, Dan :)

That site looks a bit expensive.

You want probably to look at MOSFET transistors for that...

Common transistors like the 2N3904 NPN will not be suitable for currents quite that high.

Mowcius

I want to get something from there because they have a store local to me , so I dont have to wait for shipping.

My RGB LED's should be here this week and want to be able to use them as soon as I get them, got an awesome little project to complete :D

They have a pretty good selection of stuff. I see why you want to buy from them if it is a local store.

As I don't have a lot of details about what it is going to be doing, I suggest you just look through their selection of MOSFET transistors (second or third page onwards if you search for MOSFET) and find one that looks suitable. As you have a local store then you can probably go and ask them and they may be able to recommend one.

Mowcius

Would something like this be suitable? http://www.jaycar.com.au/productView.asp?ID=ZT2466&keywords=MOSFET&form=KEYWORD

The other N-channel MOSFET's are like $23 each, and waayyyy overkill for what I need.

Basically, I have 4 RGB LED's.

All the red dies are in series with a 1 ohm resistor (to run on 12V), and the green and blue dies are in 2 series strings of 2 with a 15ohm resistor to run from 12V. They are common anode LED's, and basically I just want to be able to control the 4 LED's (At the same time, as they are all in the same colour circuit) from 3 PWM outputs.

The total draw for each colour is 1.4A, at 12V. So I need to find a transistor/MOSFET locally that I can use to PWM the LED colours.

I have some TIP41C's, but they would require around 100ma base current to drive a 1.4A load correctly, which is more than the Arduino pins can supply, but I really want to keep the component count as minimal as possible.

Thanks :)

Sorry, I have been wrong all along. They are common anode, so I can’t run them in series, I would run them in parallel, so I would be needing to switch 3V @ 1.4A, not 12V >.<

Just need to figure out the base resistors n stuff and it’s all good, I hope :smiley:

Yeah they are not cheap from there. I buy mosft of my MOSFETs for less then $2... Or in packs of 50 or so for quite a lot less.

Mowcius

Just need to figure out the base resistors n stuff and it's all good, I hope

I'm not too impressed with that drawing. It shows no current limiting resistors for the LEDs to prevent them from drawing too much current. They are sure to be damaged with that arrangement.

The best solution would be to use three logic level MOSFET transistors.

Lefty

You may try TIP122 NPN Darlington Transistor 100V 5A, with about 12mA base current will drive CE saturation.

As for the source to the LED, you can use LM317 configure as Constant current source to supply 350mA

you can use LM317 configure as Constant current source to supply 350mA

But there are 9 LED junctions, how is the constant current going to be shared if each junction is designed for 350ma each?

Lefty

I made the circuit diagram in MS word, I left the resistors out for times sake, I know very well they need current limiting.

I have decided to go with 3 2N2222A's and 3 TIP41C's to control them

Thanks everyone :)