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Topic: Using N-channel MOSFET to control LEDs? (Read 2 times) previous topic - next topic

zenwebb

I'd like to sink about 16 LEDs through an N-channel MOSFET, and I'm curious if I've set up the schematic correctly. I've only used transistors and Darlingtons before, so I'm not 100% sure if I've got this circuit just right. Do I need a resistor to ground? If so, what value?

The MOSFET I've spec'ed is: http://www.digikey.com/product-detail/en/DMN3404L-7/DMN3404LDICT-ND/2052805

Grad student, creative technologist, OSHW engineer
http://jason-webb.info

CrossRoads

Basically yes. If any one LED has a different voltage drop than its 3 neighbors, the current thru them will be unequal and may lead to failed parts.
The part you selected is not a Logic Level MOSFET, but it should work okay

42m? @ VGS = 4.5V
Check your planned current thru it to make sure it will not overheat.
Having a pulldwn to Gnd on the gate will keep it off during reset/sketch startup when the Arduino outputs are inputs and undefined (i.e. floating).
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
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zenwebb

Cool, I am planning on using all the same LED, with a maximum current draw of 1.6A. On the Digikey product page it is listed as a "Logic Level Gate", what's up with that?

I am planning to use PWM to vary the brightness, which I expected to not be a problem. Am I right about that?

Would 100ohm suffice for the pulldowns?

Grad student, creative technologist, OSHW engineer
http://jason-webb.info

zenwebb

*bump* Would 100ohm suffice for pull-downs, or would I need to spring for a 1k or 10k resistor?
Grad student, creative technologist, OSHW engineer
http://jason-webb.info

fungus


*bump* Would 100ohm suffice for pull-downs, or would I need to spring for a 1k or 10k resistor?


100ohm is much too small - an Arduino pin wouldn't even be able to pull the gate high (5V 100 Ohms allows 50mA to pass, an Arduino pin is only rated to 40mA).

10k is much better.

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