Hello, I'm designing a custom board using the sam3x8e like the arduino due uses. I need to connect a tft display and to be able to controll the brightness. Basically what must be done is to controll the backlight. The tft has a ribbon cable which the 3 first pins are for the backlight (as the datasheet tells). I'll attach a picture for you to see for yourselves.
Pin 1 = Anode for led backlight (3.3V)
Pin 2 = Cathode for led backlight (60mA)
Pin 3 = Cathode for led backlight (60mA)
Now, since it has one anode and two cathodes it means that there are 2 rows of 3 leds (possible 20mA each). I imagine that in order to controll the backlight I need to connect a pnp transistor on the first pin(anode).
My question is: What type of pnp transistor do I need? Or mabye a mosfet? I'm looking for something that can handle at least 120mA and use the smallest package available.
Some of the Due pins are very limited in current-carrying ability (I think some are 3mA even, but it varies, the datasheet of the chip has the details).
So you'll have to be careful to choose the right pin to switch your PNP transistor. At 3.3V you'll have trouble
finding a logic-level p-channel MOSFET that isn't surface-mount. If the load is 120mA you'll need a pin capable of at least 6mA and use 390 ohm base resistor to limit the base current to about 6mA.
Your link took me to a data sheet that is not what you described. Why not use a N-channel MOSFET such as a 2N7000, available in TO92. For what you are operating it should work great. Then connect the two cathodes to the drain, the source to ground and the gate to the arduino. This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!
Gil
gilshultz:
Your link took me to a data sheet that is not what you described. Why not use a N-channel MOSFET such as a 2N7000, available in TO92. For what you are operating it should work great. Then connect the two cathodes to the drain, the source to ground and the gate to the arduino. This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!
Gil
The main reason I asked for help is because I haven't used transistors in the past so I don't know much about them. Î’ased on what MarkT commented above, I found one that must work fine. (PMBT3906,215 Nexperia | C8670 - LCSC Electronics)
Well using a mosfet is an option 2. What do you think it's best? Using a mosfet or a transistor? Or mabye, if you were in my position what would you choose?
