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Topic: Lost with 50w LEDs + PWM (Read 9 times) previous topic - next topic

dc42

That schematic won't work, there is nothing to pull down the mosfet gates, also the transistors reduce the mosfet gate drive.

If the LED is common anode then you can use N-channel mosfets connected in a similar way to PWM the LEDs, but connect the mosfet gates to the Arduino PWM outputs through 100 ohms resistors (no transistors). Use logic-level mosfets. Also connect a 10K resistor between each of the Arduino PWM outputs and ground.
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fungus


The seller has answered, seems to be an expert about his products.


Doesn't really matter...

The day they arrive you can just connect a low voltage across them and find out which way lights them up. The only difference it will make is the type of transistor you need.

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

dc42



The seller has answered, seems to be an expert about his products.


Doesn't really matter...

The day they arrive you can just connect a low voltage across them and find out which way lights them up. The only difference it will make is the type of transistor you need.


Unfortunately, it also affects the circuitry needed. Common anode LEDs needing more than 5V can be controlled form the Arduino just with a N-channel mosfet or NPN transistor. Common cathode LEDs needing more than 5V require a P-channel mosfet or PNP transistor plus a level shift circuit, unless your 36V power supply has a floating output.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

Hinjeniero

#18
Jan 21, 2013, 08:12 pm Last Edit: Jan 21, 2013, 08:14 pm by Hinjeniero Reason: 1

That schematic won't work, there is nothing to pull down the mosfet gates, also the transistors reduce the mosfet gate drive.

If the LED is common anode then you can use N-channel mosfets connected in a similar way to PWM the LEDs, but connect the mosfet gates to the Arduino PWM outputs through 100 ohms resistors (no transistors). Use logic-level mosfets. Also connect a 10K resistor between each of the Arduino PWM outputs and ground.


You're right, forgot about pull down the gates. I think I fixed it.




The seller has answered, seems to be an expert about his products.


Doesn't really matter...

The day they arrive you can just connect a low voltage across them and find out which way lights them up. The only difference it will make is the type of transistor you need.


Unfortunately, it also affects the circuitry needed. Common anode LEDs needing more than 5V can be controlled form the Arduino just with a N-channel mosfet or NPN transistor. Common cathode LEDs needing more than 5V require a P-channel mosfet or PNP transistor plus a level shift circuit, unless your 36V power supply has a floating output.



I didn't know that the transistor type would change depending of if the led is common anode or cathode, I thought it would be as easy as the second schematic I made.

no pain, no gain!!

fungus


Unfortunately, it also affects the circuitry needed.


Not really. He's already using a BJT to drive the MOSFET gate. He just has to pick NPN or PNP and connect accordingly. It's not a radical change in design.

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

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