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Topic: Using TLC5940 to control 12V Strip Led. (Read 5003 times) previous topic - next topic

llluca

Hello all

as suggested on http://www.ti.com/lit/an/slva280/slva280.pdf

I had at my disposal some buz11 it work but  does not arrive at maximum intensity.
probably dosen't conduct enough.

which MOSFET  do you recommend?

thank you very much

Hippynerd

I dont know anything about your light strip, but I do know that there are many mosfets out there.
If you are looking use a mosfet with an arduino, then you need whats called a "logic level" mosfet, which basically means that it can be turned on and off with a microcontroller.

There are 2 other big factors in picking a mosfet, current limits, and speed. Those get a bit more complicated and are hard to guess when you dont know the specific needs.

websites like adafruit, sparkfun, make magazine, and instructables have documents that will help you learn more about mosfets and other transistors.
https://sites.google.com/site/rgbledcubes

OpterN

#2
Mar 29, 2013, 11:29 pm Last Edit: Mar 29, 2013, 11:31 pm by OpterN Reason: 1

Hi

I also have some questions concerning tlc5940 with 12V rgb led strip.

I'm using a strip that has three 5050 rgb leds in series with resistors for each colour per section.
Strip can be cut between the sections.

Since the strip all ready has the current limiting resistor, is there any need to use a reference resistor for tlc5940 ?
I'm planning on cutting the strip into sections and connecting them straight to tlc5940. I assume 5050 takes 20 mA per colour (I will check this later). That would be 20 mA for one channel in the tlc5940.
If the reference resistor is needed, can it be over sized, for instance allowing 40 mA ?

Result when finished should be something like this: http://www.youtube.com/watch?v=2q3vb3u75Z4

OpterN

Well I couldn't resist testing it myself.  :P

I measured about 30 mA per colour for two sections of the strip ( total of six 5050 leds).
For the reference resistor I chose 1 k. That allows 40 mA per tlc5940 channel, but since current is all ready limited by the strip it stays in 30 mA. This setting is working nicely.

Datasheet for tlc5940 says maximum current is 120 mA, when using 5 V. Is using 120 mA for a channel totally safe or should it be little less than 120 mA? What would be maximum current for a channel, if  want to play it safe?

llluca



I measured about 30 mA per colour for two sections of the strip ( total of six 5050 leds).



I would suggest  for your project NeoPixel .

Grumpy_Mike

Quote
I had at my disposal some buz11 it work but  does not arrive at maximum intensity.
probably dosen't conduct enough.

How have you wired them up?
You need at least 10V with a BUZ11 FET to turn it on. This can be handled by this chip if you feed the inputs from a resistor going up to between 10V and 18V.
Note driving a FET from a TLC5940 means the signal is inverted. As this chip never fully turns on the LED you will find that with the inversion you can not fully turn off the LED. 

llluca


How have you wired them up?

as suggested on pdf,
but in my opinion     it not working correct, it doesen't  give the full power.

Now I was thinking about a circuit with BC547 and Buz11

Grumpy_Mike

That PDF is not about driving an output through a FET is is about using voltages higher than 18V.
So what is your actual wiring and what current are you asking the TLC chip to supply?
Do you know if this is enough to give you full brightness?

mjkzz


Quote
I had at my disposal some buz11 it work but  does not arrive at maximum intensity.
probably dosen't conduct enough.

How have you wired them up?
You need at least 10V with a BUZ11 FET to turn it on. This can be handled by this chip if you feed the inputs from a resistor going up to between 10V and 18V.
Note driving a FET from a TLC5940 means the signal is inverted. As this chip never fully turns on the LED you will find that with the inversion you can not fully turn off the LED. 


I took a look at BUZ11, it seems it can handle about 2A at Vgs=4V and close to 9A when Vgs=5V according to datasheet, figure 6.

www.mjkzz.com
www.pylin.com

llluca


Do you know if this is enough to give you full brightness?

thanks now I understand the tlc5940  limits the current as by resistance on pin 20, for  this reason I had a low brightness!

thank you very much

@  mjkzz
afaIk  buz11 have 30 A and  50 V for   max power 75 W

mjkzz



Do you know if this is enough to give you full brightness?

thanks now I understand the tlc5940  limits the current as by resistance on pin 20, for  this reason I had a low brightness!

thank you very much

@  mjkzz
afaIk  buz11 have 30 A and  50 V for   max power 75 W


Yes, but it depends how you are driving it. If your Vgs is around 5V, you are not going to get 30A. To drive it at 30A, you probably need a MOSFET driver to up the Vgs to 20V.
www.mjkzz.com
www.pylin.com

llluca


need a MOSFET driver to up the Vgs to 20V.


exactly!  for this reason  I am going to use a BC547 to drive my buz11.
and it  seems to to do his job  :)


thanks for all  yours  aids

mjkzz



need a MOSFET driver to up the Vgs to 20V.


exactly!  for this reason  I am going to use a BC547 to drive my buz11.
and it  seems to to do his job  :)


thanks for all  yours  aids


How much current do you need?

A 5 meter long 12V LED strip draws about 2A each channel, with BUZ11 and 5V Vgs, it should work because from Figure 6 of the datasheet, it can handle close to 9A.

Just saying.
www.mjkzz.com
www.pylin.com

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