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Author Topic: PWM driver Tlc5940 with mosfet  (Read 1868 times)
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I want to PWM all my interior lighting.
For that I need allot of PWM pins. The Tlc5940 IC seems to be a populair choise.

With the Arduino PWM pins I could use a mosfet like this one (IRLZ34NPBF) directly on that pin, it delivers enough power.
But I' am not sure about the Tlc5940. Is the PWM frequency higher than an Arduino PWM pin output, is it to high to drive a mosfet?
Can the Tlc5940 drive a N channel mosfet like this one: IRLZ34NPBF ?

Is a mosfet driver like this one needed: SN74LS04N ?
If so, where can I find a toturial on how to use one?

Thanks for any help!
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is it to high to drive a mosfet?
No

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Is a mosfet driver like this one needed: SN74LS04N ?
No

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Can the Tlc5940 drive a N channel mosfet like this one: IRLZ34NPBF ?
Yes

BUT
By doing this you invert the signal from the TLC5940. No problem you might think but there is a small blank period always present. When you invert the signal this translates into the LEDs always being slightly on. In other words you can't turn them completely off. So either live with it or invert the signal with something like a 74LS04 before applying it to the FET.
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Hi,

I' am new to this, just a beginner with electronics.

The invert problem, I have not noticed that when driving a mosfet of a PWM arduino pin.
Is it only inverted when the Tlc5940 is used?

I want to completly turn the lights off.
Is the 74LS04 the best choice? Is it not only inverting the signal, but also able to drive higher power mosfets to?
And how can I use the 74LS04? Any tutorials?
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The invert problem, I have not noticed that when driving a mosfet of a PWM arduino pin.
You won't it is only a problem with the TLC5940 due to the way it works not the fact it is producing PWM.

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And how can I use the 74LS04? Any tutorials?
I would doubt anyone would produce a tutorial for this it is too simple. The 74LS04 has six inverters in it so that means you can drive six FETs with one chip. Take one of the inputs and attach it to one of the outputs of the TLC5940. Also wire a resistor say 3K from the input to +5V. Then take the output from that inverter and wire it directly to the gate of the FET. You also need to wire the 74LS04's pin 14 to +5V and pin 7 to ground.
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Ok, that sound simple enough.

But is the 74LS04N a mosfet driver or only an invertor?
Is this better for higher PWM frequencies and higher power mosfets, or is it as good as an normal Arduino pwm pin?
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But is the 74LS04N a mosfet driver or only an invertor?
It is designed as a logic inverter, it is slightly better than the arduino pin in that you don't need a series resistor to limit the inrush current because the outputs are rated for a short circuit to ground load. They are not designed as a FET driver although at the speeds / load currents you are using there is no need for a FET driver.
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Ok, thanks for the information.
I can choose between SN74LS04N http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=296-1629-5-ND and SN74LS06N http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=296-15069-5-ND. The last one has an Low, High output 40mA, 40mA.
Can this logic inverter deliver more power, but uses no more power from the arduino pin than the first one?
Are they of the same switching speed?
Maybe for higher power mosfets in the future choosing a 40mA in stead of a 16mA might be usefull? Price isn't much difference, so if there is no down side to the 40mA model I rather choose that one.
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Can this logic inverter deliver more power, but uses no more power from the arduino pin than the first one?
Yes, more current actually it is not appropriate to talk of power here even though technically that is what is happening.
But you don't need this increase in drive capacity do you?

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Are they of the same switching speed?
Yes all 74LS devices operate at the same fundamental speed.

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