High Current Shift Registers

Discussion in 'General Electronics Chat' started by kelvinmead, Oct 4, 2012.

  1. kelvinmead

    Thread Starter Member

    May 15, 2011
    30
    0
    hi,

    im doing a project with a set of 12v strips leds.

    im creating an led matrix from these, in a multiplex formation.

    ive worked out that i need to use shift registers from my arduino to trigger the leds, but i know that the usual 74hc595 can't SINK the current, so ive plopped in there a direct replacement TPIC6B595, and this works fine.

    but on my SOURCE line, i can't get my head around a replacement.

    ive been pointed in the line of the 74HC595 with the ULN2803, or a TC4427, but both of these I'm having no luck.

    is there a direct opposite for the TPIC6B595 in current SOURCE?
     
  2. MMcLaren

    Well-Known Member

    Feb 14, 2010
    759
    116
    hi kelvin,

    The only high current/high voltage serial-to-parallel source driver IC that I've come across is the Micrel MIC5891. One of the features I like best is the separate VBB and VCC supply pins which make it particularly easy to drive high voltage multi-LED per segment displays or matrices. For example, the logic diagram below shows a display subsystem with a six pin microcontroller interface using several Micrel MIC5891 ICs to drive large 24 volt multi-LED per segment common cathode displays (with complete fade-to-black PWM brightness control).

    Good luck with your project.

    Cheerful regards, Mike
     
    Last edited: Oct 5, 2012
  3. ScottWang

    Moderator

    Aug 23, 2012
    4,854
    767
    When you used ULN2803, then the data must be opposite from 74HC595, did you do that?

    ULN2803 - you can treat it like an inverter.
    TC4427 - this is a two non inverting buffer.

    I am not sure what's going on when you used TC4427, sometimes we have to using scope to measure the in/out signal.
     
  4. kelvinmead

    Thread Starter Member

    May 15, 2011
    30
    0
    bit over my head here.

    how do you mean the data must be opposite, like if i want the led to light i must send an OFF/LOW signal?
     
  5. ScottWang

    Moderator

    Aug 23, 2012
    4,854
    767
    LED lighting(ON) voltage:

    74HC595 Hi → Hi Input ULN2803, ULN2803 Vo Lo(OC) ← LED(-) --<|-- (+)LED ← R ← +V

    LED Extinguish(OFF) voltage:

    74HC595 Lo → Lo Input ULN2803, ULN2803 Vo Floating(High Impedence) -- LED(-) --<|-- (+)LED -- R -- +V

    R - Limited current resistor.
    OC - Open Collector.

    The arrow showing the current direction.

    If you add the pnp transistor to control the +V side for the LED, then the current should be like this:
    LED lighting(ON) voltage:
    74HC595 Hi → Hi Input ULN2803, ULN2803 Vo Lo(OC) ← LED(-) --<|-- (+)LED ← R ← C of PNP ← E of PNP+V.
    B of PNP connecting a R to the MCU port or some drivers.
     
    Last edited: Oct 6, 2012
  6. kelvinmead

    Thread Starter Member

    May 15, 2011
    30
    0
    i can see the workings out, but my brain understands picturez better...

    is this what you mean?

    [​IMG]

    i have omitted the sink 74hc595 as the tpic is working without the use of the 2803.

    it is the positive side of the equation that i am confused about.

    well, i say confused... ive ordered some of the above mentioned chips, but i would like to know how to do 0something without having to just buy the exact part every time!!

    lol
     
  7. ScottWang

    Moderator

    Aug 23, 2012
    4,854
    767
    You didn't look the arrow more carefully, because the arrow showing the current(EE Parts) direction.

    The function of TPIC6B595 is similar as ULN2803 or ULN2003, but the ouput drivers of TPIC6B595 are N type MOSFETs, and the output drivers of ULN2803 or ULN2003 are NPN transistors.

    Their output are all current sink, it means that their current sink from next stages or LED or some other devices.

    You can't put two sink drivers in a circuit, you should used one is output current and another is sink.

    The circuit shows as following can be use in many different parts:
    The left side are the input, they can be 74HC595, and the right side are the output, they can drive the positive voltage to the +V of LEDs

    [​IMG]


    How to use ULN2003 and ULN2803 to drive The LEDs.
    [​IMG]
     
    Last edited: Oct 9, 2012
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