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1. 

   tmbomber
   Member

   Last month I blew up the regulators on two Maple boards because I was directly driving three LEDs from digital output pins (and powering the board from a 12VDC source)

   I'm looking for a way to do this without having the current powering the LEDs source from the on board regulators. My plan is to power the LEDs from Vin and use NPN transistors to switch the ground side of them. The schematic I just completed uses 2N2222 NPN transistors with 1K resistors in series with their gates to cut down the current that the digital lines have to source.

   Everything *looks* OK, but I thought I post something here asking if there's anything else I've overlooked or if anybody has a better suggestion on what transistor to use. (I was thinking N channel MOSFETs might be better, but haven't looked yet)

   Looking to use only through hole parts as I'm putting together a kit for others to solder together.

   Thanks!

   Posted 3 years ago #
2. 

   Anonymous
   Unregistered

   There is a one chip solution to your problem, The TM1638. Currently $1.50 each on eBay.
   This chip is capable of driving 10 seven segment LED's, 80 separate LEDs, "8 x 10 matrix" Or a combination of seven segment LED's and single LEDs. It also provides a 3 x 8 matrix keyboard,and a software controlled LED Intensity control. All using a serial interface that can be daisy chained.

   Arduino drivers are available but need to be converted to the Maple platform.

   There is also several examples using this Chip on YouTube.

   Note: there are several other chips that can do the job as well, this is just the cheapest.

   Hope this helps.

   Posted 3 years ago #
3. 

   gbulmer
   Moderator

   tmbomber - I'd use an NPN transistor array, like a ULN2003, or similar like uln2803.
   They come in DIP-packages, so they should be easy to use.

   They need external resistors to current limit the LEDs, but do have the internal resistors to bias the (Darlington) transistors, so not many components.

   Because they are Darlington transistors, they will take about a mA to switch each one on, so shouldn't cause much load on the MCU.
   There is no programming.

   ULN2003 are less than $0.20 for seven switches.

   Posted 3 years ago #
4. 

   konan
   Member

   For driving single LED, I use the 2N7000/2N7002 transistors. The 3.3V output from the STM32 is quite enough to open it at 20-30 mA LED current. For more powerful LEDs, of course, you need to use more powerful transistors. And, there are nice LED current drivers from ON Semiconductors, NSI45xxx and NSI50xxx series. They can be simple used instead of resistors.
   For more complex projects, there are Macroblock's MBI series chips. I worked with MBI5040. They are not very cheap, but one chip can directly (without resistors) drive 16 channels of LEDs with 16-bit PWM, at voltage up to 17V, and communicate with the processor via "almost SPI" :) The serial protocol they're using has some difference from the classical SPI, but it's not a problem, you just need to manage SS line manually.

   Posted 3 years ago #

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