Would Mosfet Help me in my Led Project

Other Hardware LEDs and Multiplexing
1

Hello,

While using a DUE arduino card, one of the part of my project is to use 8 Led 4-pin with Common cathode (I can't change it).

All the Led needs to have the same light at all time, the number of PWM pin here is not the issue (1 for each color) but the issue is the current used by all the LED. each of the color use 20mA (*8 = 160mA).

What are easy solution I have ? I never used Mosfet transistor, could they help me ? If yes would you have a reference ?

Thank you !

2
  • Always show us a good schematic of your proposed circuit.
3

You will need 3 transistors.

Because your LEDs are common cathode, you should use either PNP BJT transistors or P-channel MOSFETs.

I would recommend 3x BC327 PNP transistors. You will need a resistor for the base pin of each transistor.

You will also need 24 resistors. The resistors for the R pins on the LEDs should have a higher value than those on the G & B pins.

4

Definitely Yes. However we can't provide more information unless we know how you are connecting things. A simple hand sketch in schematic form would be fine. You can google schematic for examples.

5

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Here is the simplified shematic, I hope it helps

6

  • So the controller will be driving 8 RGB LEDs.
    All the LEDs are to be operated in parallel i.e. if one LED is orange, all the LEDs will be Orange ?

  • What LEDs did you select ?

  • Are you comfortable in soldering SMDs ?

7

Those cannot be powered by the DUE. You need to implement drive "B" with one led color replacing the motor and diode.

So you will need three "B" drivers, one for each color.

BTW the below is not my creation and I don't remember who to cite for this very useful drawing.

MosFet Drive Variations (annotated)
MosFet Drive Variations (annotated)2128×1600 271 KB

8

That could be a problem for the blue LED with a 3.3volt-logic Due.
There is no overhead voltage to drive a 3.3volt LED with a 3.3volt pin with a controlled current.
A (cheaper) Mega (5volt-logic) would have been a better choice.
Leo..

9

Yes the controller will be driving the LED by PWM, All have to be the same color at all time.
I can use an external power supply if needed.

The led i am using are these

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image
image681×497 101 KB

I'd rather not solder SMDs

10

well I actually have a MEGA arduino card I could use but for some reason it doesn't want to upload any code.. Would it make everything easier ? How so

11

Thank you for sharing, but the shematic looks like is to drive motor or servo isn't ?

12

I have a very simple solution.
Use a TBD62783A . It is an 18 pin DIP IC, easy to use in a breadboard.
You will need 3 of them and resistors

image
image722×598 7 KB

13

How much is the current source for each pin of the device?

14

If you need help with my circuit just let me know.

16

Thank you very much.. I really appreciate. I just wonder what is the benefit of taking the *TBD62783A over PNP transistors ?

Thank you !

17

Much much less wiring

If you use PNP then you would also need NPN to drive them, so you would have a total of 48 transistors to wire up, including a lot of resistors.

You might only need one if all the LED can only be one color at a time.