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Using tlc5940 product as constant and similar current drive for multiple leds

Ammar Kadhim
Prodigy 50 points
Other Parts Discussed in Thread: TLC5940, TLC5921

Hi,

I would like to drive similar 6 led-based parallel sensors at constant current and in continuous mode without bothering about pwm or dc setup and I am wondering if I can still use tlc5940 chip. Also is it possible to control leds to operate in single, 2, 4 and 6-channel modes. Other similar products that have less output channel than tlc5940!

I appreciate your feedback about these concerns

 

 

  • 0
    TI__Guru 61685 points

    Hello Ammar,

    When you say you want to drive the LED-based sensors in continuous mode, does this mean you just want to turn the sensors on an off? If you could give more information about the usage of the sensor and the voltages you have available and the sensors need, it would be easier to answer your question.

    TLC5940 can drive each channel with a constant current, but you need a controller to deliver the grayscale and dot correction data.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 50 points

    Hi Brigitte,

    continuous mode meant having the leds turned on at constant brightness during measurement. The required voltage is 5 volts and current is 30+/-5 mA for each led. each. I search about the dot correction and it looks that it is the only way to drive the leds at constant and same luminous and in turn has to be controlled by processor or controller.

    many thanks and sorry for the late reply

    Regards ... Ammar

  • 0 in reply to Ammar Kadhim
    TI__Guru 61685 points

    Hello Ammar,

    You might have a look at TLC5921 if you do not need to regulate the individual output current to a different value. With this part, the constant current is set by a resistor for all channels and then the outputs are just either turned on or off.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 50 points

    Hi Brigitte,

    I am aiming to achieve similar and constant brightness from each led. Based on my understanding to article of TI slyt225.pdf (TLC5940 dot correction compensates for variations in LED brightness) that despite the similarity of the utilized LEDs (specs and manufacturing) the dot correction technique is always required for achieving similar and uniform brightness due to the LED variation of the delta in lumens (20-15%) and the decay rate. Hence and before any further revision, I am going to purchase both tlc chips (tlc5940 & tlc5921) and other brands (LM3432 and MAX16807) as well as the similar led sensor probes for my designated system, construct the circuit and run the appropriate tests. Then based on the obtained brightness uniformity of the sensors I will decide whether dot correction is essential or not.

    One more question, is there tlc led driver chip with less channels (say 10) than 16!

     

    Many thanks for your comments and feedback and have a great time

     

    Regards ... Ammar

  • 0 in reply to Ammar Kadhim
    TI__Guru 61685 points

    Hello Ammar,

    There are LEDs on the market that are preselected to make sure that the fit relatively close to each other in brightness. The closer they fit, the more expensive the LEDs are. Therefore for screens where each LED is controlled individually by a current sink, dot correction is the better and less expensive solution compared to selected LEDs. If you have a limited amount of LEDs, it might be not a problem when the brightness varies a bit and therefore the selection of LEDs might be a good solution.

    For finding other TLC parts, please check out the Lighting and Display Solutions webpage from TI: http://focus.ti.com/paramsearch/docs/parametricsearch.tsp?family=analog&familyId=690&uiTemplateId=NODE_STRY_PGE_T

    Best regards,
    Brigitte