Arduino Forum

Using Arduino => LEDs and Multiplexing => Topic started by: toxsickcity on Feb 16, 2018, 02:51 am

Title: TLC5940 and MOSFET IRFZ44N Pullup Voltage? Flicking!! :(
Post by: toxsickcity on Feb 16, 2018, 02:51 am
Hi all,

I am having issues with TLC5940 and the MOSFET IRFZ44N
I brought some TLCs so I can expand on the PWMs as I have a requirement to run more then what my arduino boards allows.

Some strings of LEDs only have 6x 5050s on it, some with about 30x 5050s

I am thinking of dividing the workload accordingly. and might be able to ignore use of MOSFETS on the TLC entirely if running 6 LEDs on a string wouldn't overload an output. The Strings with MANY LEDs I can run via Arduino MEGA PWM Output-->MOSFET

When I use a standard 2 Colour LED connected to the TLC works fine, when my thermal sensor warms up the led changes from Blue to RED as I intended, I have some flickers but will attempt to resolve this later,
If anyone can suggest help here also, RE Flickers.. (flicker happens during a very slow transisition from Fading from BLUE to RED.. (My code seems to be fine as when I drive the same program via Arduino-->Mosfets, the flickers dont exsist!) I was told to use a capacitor on GND/5V inputs of the TLC, this did not help.. I used a 20uf 10v Cap.

Please refer to my attachment for my wiring diagram and setup of the TLC... for testing purposes I am using an UNO and only 1pcs of TLC and copied wiring as to the photo.

When use TLC I cannot get the Mosfets to run my LED Strings and I read a post stating I need to pullup the voltage.
https://forum.arduino.cc/index.php?topic=418269.0 (https://forum.arduino.cc/index.php?topic=418269.0) the Last Post...
I didnt know the TLC was not setup to drive mosfets and I read I need to pull up to 5v it is the TLC's outputs that need to be brought to 5v?
I tried this with a 1.5K Resistor only the LED String turned ON... (At the time of connection, only one of the 2 Colours should have been active but both turned on) so i am assuming didn't work.




I have some questions,

Would the TLC output run a string of LEDs with only 6x 5050s @ 12v?

What would be the most LEDs on a string of 5050s I would be able to approx. run?

How do I run my TLC close to it's maximum output power?
(I am reading TLC has 40mA or 120mA) I am confused.

can anyone guide me to resistor sizes and capacitor sizes for fixing flickers and doing the pullup of the output.


thanks shaun
Title: Re: TLC5940 and MOSFET IRFZ44N Pullup Voltage? Flicking!! :(
Post by: PaulRB on Feb 16, 2018, 08:10 am
(http://forum.arduino.cc/index.php?action=dlattach;topic=529518.0;attach=245691)
Where are the MOSFETs?
Title: Re: TLC5940 and MOSFET IRFZ44N Pullup Voltage? Flicking!! :(
Post by: toxsickcity on Feb 16, 2018, 08:54 am
This is how I setup MOSFET. exactly same way I would if I was driving them from the arduino pwm out 2,4,5,9,10,11

mosfet resistors are 10K

I also tried 1.5K & 10K on the Positive and TLC5940 output..




Title: Re: TLC5940 and MOSFET IRFZ44N Pullup Voltage? Flicking!! :(
Post by: septillion on Feb 16, 2018, 09:46 am
Ca you make a real schematic? This Fritzing mes isn't making it very clear. If you con't know how to do that on the computer(Fritzing can do it ;)) just use pen and paper.
Title: Re: TLC5940 and MOSFET IRFZ44N Pullup Voltage? Flicking!! :(
Post by: toxsickcity on Feb 16, 2018, 09:55 am
ive decided to piss off these stupid chips and just brought a 2nd MEGA..
the chip seems too unstable and can imagine the computer is going to look shit with flickering lighting.. I have read nightmare after nightmare..

sad I wasted my money on these and should have done my research

I just wish arduino could use all it's digital pins as PWM..
Title: Re: TLC5940 and MOSFET IRFZ44N Pullup Voltage? Flicking!! :(
Post by: septillion on Feb 16, 2018, 09:57 am
Those chips are just fine. It's just your lack of skill to work with them ;)
Title: Re: TLC5940 and MOSFET IRFZ44N Pullup Voltage? Flicking!! :(
Post by: septillion on Feb 16, 2018, 10:40 am
Those chips are indeed not the easiest to use. Fine to drive small loads directly (the constant current driver in them is great for that) but driving mosfets get's complicated. I would jut switch them for a simple PWM chip like the PCA9685.

And I would also learn how to daw a real schematic :)
Title: Re: TLC5940 and MOSFET IRFZ44N Pullup Voltage? Flicking!! :(
Post by: LesserMole on Feb 16, 2018, 11:59 am
I didn't understand the half of all of that, but it might be worth pointing out that the IRFZ44 isn't a logic level transistor. You may be confusing it with the IRLZ44, which is.

(https://forum.arduino.cc/index.php?action=dlattach;topic=529518.0;attach=245736)

(https://forum.arduino.cc/index.php?action=dlattach;topic=529518.0;attach=245738)
Title: Re: TLC5940 and MOSFET IRFZ44N Pullup Voltage? Flicking!! :(
Post by: septillion on Feb 16, 2018, 01:26 pm
IRFZ44 can work fine only keep in mind the limited current you can switch and possibly higher losses.
Title: Re: TLC5940 and MOSFET IRFZ44N Pullup Voltage? Flicking!! :(
Post by: LesserMole on Feb 16, 2018, 01:39 pm
IRFZ44 can work fine only keep in mind the limited current you can switch and possibly higher losses.
work fine != (limited current and higher losses) ;)

If the datasheet doesn't list a 5V Rds(on) surely you can't rely on it being a particular value and can't calculate what that "limited current" may be at 5V.

Why not just get the L-version?

Title: Re: TLC5940 and MOSFET IRFZ44N Pullup Voltage? Flicking!! :(
Post by: septillion on Feb 16, 2018, 01:45 pm
It doesn't it there but you can see it in the graphs just fine :)

I agree, if you need to get one, get the L version. But if you pulled it from the spare parts drawer it's fine, jus look up the limitations.
Title: Re: TLC5940 and MOSFET IRFZ44N Pullup Voltage? Flicking!! :(
Post by: LesserMole on Feb 16, 2018, 02:04 pm
It doesn't it there but you can see it in the graphs just fine :)

Oh yeah, good point, I always forget about the graphs, just look at the tables....

Title: Re: TLC5940 and MOSFET IRFZ44N Pullup Voltage? Flicking!! :(
Post by: toxsickcity on Feb 19, 2018, 03:37 am
IRFZ44 can work fine only keep in mind the limited current you can switch and possibly higher losses.
Hi Septillion,

Can you advise how to properly wire the IRFZ44 to the TLC5940?

If I can make the TLC5940 output to a ordinary LED. the TLC is working correctly. I only wish to use a high load LED string via the mosfet.

You mention it will work fine?

I wish to attempt one last try.
Title: Re: TLC5940 and MOSFET IRFZ44N Pullup Voltage? Flicking!! :(
Post by: septillion on Feb 19, 2018, 10:09 am
Thing is, a TLC5940 can only sink current. If you use a N-channel low side, you need a pull up on the gate to enable it and use the TLC5940 to pull it low. This will inverse the logic! And because the gate will only rise via a pull up this might give you some extra heat because of the slope.
Title: Re: TLC5940 and MOSFET IRFZ44N Pullup Voltage? Flicking!! :(
Post by: Grumpy_Mike on Feb 20, 2018, 09:43 am
The inverted logic means you can never turn the LEDs off completely. This is because in normal operation you never turn them on fully, but one step off full brightness which you do not notice. However on step off from zero you can see as a faint glow.
Title: Re: TLC5940 and MOSFET IRFZ44N Pullup Voltage? Flicking!! :(
Post by: septillion on Feb 20, 2018, 09:50 am
That can indeed be an issue. Easiest fix is to use P channel and drive high side. But that's not an option for common anode leds.