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Looking for an LED driver recommendation

colporteur

image

I'm looking for some suggestions on a replacement LED driver circuit for the one above..

I have 10 common cathode tri-colour LEDs I need to drive. I banged out this transistor circuit to isolate the LED's from the Arduino. A HIGH output from the Arduino should light the LED. I've used the transistor circuit on a small scale for driving LEDs. My formal training was in electronics but 20 years ago my career forked to computer networks as a system administrator and the electronics became a thing for hobbies.

I then thought there has to be an easier way. I started newark searching for possible drivers but my lack of practical experience in this area makes it tough. I'm looking for something simple that takes the load of the microcontroller. I found this SN74HCT245N bus driver and thought that might work. Four twenty pin IC's would give me 32 drivers. I need 30 in total. Simple IC's verses all the individual components would make PCB assembly definitely easier.

This is not high speed switching. It is simple on and off control for LED's. I'm hoping the folks that hang out here and do this sort of stuff all the time would have a recommendation for there go to circuits for this sort of thing. 

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  • 0

    Hi https://community.element14.com/members/colporteur,

    If I've understand you, your Arduino sends a HIGH from its output-pins.

    Are the RGB-LEDs common cathodes, then you will need consider three points.
    1) you need a logical inverter
    2) you need a high side driver with PNP transistors, with that you can drive the common cathode LEDs.
    3) power dissipation. What kind, type are your RGB-LEDs? High- or Low current?

    possible Solution: - if you drive just direct the LEDs -
    1) simple inverters connected on the Arduino
    2) your high-side drivers needs e.g. BC557 or similar, or for more current BC327, or similar
    -> with this, you can drive with high current

    A ULN2xxx does not work because they are low side drivers (darlington NPN outputs)
    A 74 xx245 does not work because this is a tri-state bus driver.

    If you drive the LEDs storing the logical states, then a MAX7219 (SPI bus with Load-pin) or a MAX7221 (SPI-bus with /CS-pin) will work,
    but it has a serial input and a driver matrix output. Both drives have a DI-pin and DO-pin, so you can use it daisy-channed.
    Here you need more program code, but you can save pins on the Arduino.

    Consider the power dissipation!
    If you cannot reach, you will need external high current drivers; see point 3. Please read the datasheet (a sample schematic is shown).

    MAX7219/7221 datasheet:

    A possible way can also be using the serial-parallel decoder 74HC595.

    With this decoder - driver you can make your schematic very simple.

    As well here - Power dissipation, this driver can drive just low-current LEDs.

    Well, .... :) ... the PCB grows more complex.

    Best regards
    Gerald

  • 0 in reply to geralds

    My criteria is minimum components. UDN2981A is a source driver so it should be able to control the LEDs' with only resistor.

    I looked at the two IC above and found a SN74HCT244N driver. With a resistor for each LED I am in business I think.

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  • 0 in reply to colporteur

    Yes, I thought this too. 

    How many pins have your Arduino (which type of Arduino?) for the LEDs? I think you have not 30 pins for the LEDs (10 RGB LEDs).

    How much current does they need?

    >> If the RGB LEDs are low-current LEDs (<5mA) then you can drive this with 4 ICs 74HC595, connected in daisy-chain.

    The source code is a 30-step, serial to parallel decoding. On the Arduino you need only few pins.

    If you have higher current LEDs >>> The driver between the 74HC595 and the LEDs are the MIC2981 (this is the Microchip version, because the UDN (Allegro) is obsolete). So, you have then 8 ICs.

    -> One point: may be the SRCLK needs a delay between the 595's because H'7 and the SRCLK can have a problem synchronizing from the first to the next step.

    https://www.ti.com/lit/an/scea117/scea117.pdf

    (please read page 10 and 11 in this application report)

    May be 1 buffer IC would be adding to the schematic.

    This is what I thought for your schematics.