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Topic: TLC5940 & IRFZ44N (Read 1 time) previous topic - next topic

jammerxd

Hello,
I recently found the TLC5940NT IC and it adds as many PWM channels as you need to your arduino. Each IC adds 16 so if you add 2 TLC5940s daisy chained together, you get an additional 32 PWM channels.

I currently use IRFZ44N transistors off of the arduino(mega or uno) to allow for 12v RGB LED strips to be controlled.

My question is: Can I use the IRFZ44N N-Channel MOSFET Transistor with the TLC5940NT IC on the outputs of each of the PWM channels it provides? If not, is there a transistor that allows me to hookup the LEDs in a similar fashion?

Datasheets
-----------
IRFZ44N: http://pdf.datasheetcatalog.com/datasheet/irf/irfz44n.pdf
TLC5940NT: https://www.sparkfun.com/datasheets/Components/General/tlc5940.pdf


Fritzing ZIP File of current transistor schematic: https://drive.google.com/file/d/0ByvuzqdDIHyvdjFheUNURk5KUHc/view?usp=sharing


Please let me know if any additional documentation is needed.

septillion

You can hook up 12V strips directly. But only 120mA per output... It that's not enough you can try to use the IRFZ44 with a pull up resistor to 12V (the TLC can only sink current) to amplify if. But is will invert the PWM and you might not be able to dim fully to off because the leds will now be on in a blank period.
Use fricking code tags!!!!
I want x => I would like x, I need help => I would like help, Need fast => Go and pay someone to do the job...

NEW Library to make fading leds a piece of cake
https://github.com/septillion-git/FadeLed

Wawa

It seems you're using the wrong parts to control LED strips.
That chip if for direct driving small LEDs (sink only).
And the fet is not a logic level fet, so can't be driven with 5volt logic.

A PCA9685 breakout board (Adafruit or ebay) could do what you want.
16 channels of 12-bit PWM with 2-wire I2C control.
It can directly drive the logic level mosfets for your LED strips.
Leo..

jammerxd

#3
Aug 14, 2016, 01:09 am Last Edit: Aug 14, 2016, 01:19 am by jammerxd
Would I be only using the PWM pin of each output or would the LEDs HAVE to go through the V+ and GND pins for each channel as well...or could I do the same wiring schematic as my arduino just instead of an arduino, I'm using the PWM and GND of the PCA9685???

Also I was wrong in the type of transistor I am using, I'm actually using IRL540s: http://www.digikey.com/product-detail/en/vishay-siliconix/IRL540PBF/IRL540PBF-ND/812025
http://www.vishay.com/docs/91300/91300.pdf

MOSFET:

Gate --> PWM ON PCA9685
Drain --> LED R, G OR B ON STRIP
Source --> GND

Grumpy_Mike

Quote
Would I be only using the PWM pin of each output
Yes.

Quote
could I do the same wiring schematic as my arduino just instead of an arduino,
There are two ways to wire up an LED to the Arduino, sourcing current ( most beginners use this ) and sinking current. With the PCA9685 you have to use current sinking. That is anode to +5V and cathode to the PCA9685 output.

Wawa

#5
Aug 14, 2016, 03:29 am Last Edit: Aug 14, 2016, 03:31 am by Wawa
The PCA9685 is not really made to drive small LEDs directly. Like an Arduino pin, it has no current limiting.
Grumpy_Mike is right. The chip can indeed sink more current than it can source.
Not important if you use logic fets to drive e.g. a LED strip.
I would add a 220ohm resistor between chip output and gate to limit switch currents.
A good LED library can be found here.
Leo..

septillion

Why are newbies always great in ignoring posts they don't understand it....

But I agree the PCA9685 would make more sens here. But If you plan to makes a lot of channels I would switch to a dual SMD package like the the IRF7313.

And the fet is not a logic level fet, so can't be driven with 5volt logic.
That's why I suggested to pull it up to the 12V line :D
Use fricking code tags!!!!
I want x => I would like x, I need help => I would like help, Need fast => Go and pay someone to do the job...

NEW Library to make fading leds a piece of cake
https://github.com/septillion-git/FadeLed

Wawa

That's why I suggested to pull it up to the 12V line :D
Then you also have to explain open collector outputs and inverted logic.
Difficult concepts for a newbie.
Leo..

Ontaelio

To answer the original question: yes, surely you can.
Two things to note:
1) use a pull-up resistor on all the LED driver channels (gates); pull them to the same voltage as the Vcc input on your LED drivers (I use 5v);
2) the logic will be inverted, namely 4095 for no light, 0 for full brightness. Because of this you'll want to add a master MOSFET on the 12v line that will keep it closed until your contraption is ready for work, because if you don't, all the strips will turn fully on on startup (producing bright white). Not nice and too much strain on your power supply.

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