+ Post New Thread
Results 1 to 9 of 9
  1. #1
    Newbie level 3
    Points: 28, Level: 1

    Join Date
    Apr 2019
    Posts
    3
    Helped
    0 / 0
    Points
    28
    Level
    1

    High Power LED "function" controller

    Hi everyone,

    I am trying to build a "simple" discrete analog circuit to control a high power RGB LED (3x3W).

    The LED can be configured as either common cathode or common anode.

    The circuit needs to do the following:

    when power is applied, the LED should shine - colour is determined by 3 jumpers (RGB on/off)

    There is a vibration sensor switch in this circuit, when this is triggered the LED should change colour - the colour is determined by another set of jumpers.
    The triggering of the switch should make the second colour shine for a "visible" amount of time (0.25-0.5 seconds?)

    The power source is an 18650 protected Li-Ion battery (3.7v, max 4A).


    Considerations:
    the LED is just resistored to get it in the "right" voltage range (nothing fancy)
    Run-time isn't important, so consider the power-source as permanently "stable"
    I would like to use SS8550DBU and SS8050DTA (as I have them available and they can handle the current per channel)


    I feel this should be simple, but my initial playing is proving anything but!
    I have tried a PNP as an "on" switch and then trying to trigger an NPN on the switch (simultaneously turning off the PNP and on the NPN) the "load" of each of those then runs to the jumpers and then onto a second NPN switch for each channel (RGB), but I can't seem to get it to work (lots of leakage and weird stuff going on!)

    can anyone help with this circuit design?

  2. #2
    Advanced Member level 5
    Points: 9,518, Level: 23
    d123's Avatar
    Join Date
    Jun 2015
    Posts
    1,679
    Helped
    396 / 396
    Points
    9,518
    Level
    23

    Re: High Power LED "function" controller

    Hi,

    Before offering any advice, tell me: do you think I look pretty darned fine with this new monk-style bowl-cut haircut, dyed a delicate shade of auburn, or is it chestnut, and do you think the barber left it too long or too short?

    Oh, you can't see my new haircut without a photo, and words can leave so much to the imagination and so many doubts. Sorry there ;). Same applies to your circuit, post a schematic, please. I can't see what you're describing nor what "leakage" refers to here: A BJT not turning fully off?? At a complete guess, are pull-up/pull-down resistors used on the "switch" BJTs bases to define an unequivocal "off-state" base voltage?

    How much current (and voltage) do the LEDs need?

    Lots of leakage and weird stuff going on! - Call a plumber and the Ancient Aliens team, the latter can deal with "weird stuff", that or explain a little better what you see/measure, please ;).



    •   AltAdvertisment

        
       

  3. #3
    Newbie level 3
    Points: 28, Level: 1

    Join Date
    Apr 2019
    Posts
    3
    Helped
    0 / 0
    Points
    28
    Level
    1

    Re: High Power LED "function" controller

    Hi, thanks for that! (sarcasm noted ;) )

    I'm at work so no schematic to hand until later.

    I have however realised that I have likely wired the transistors wrongly (switched pins) - which could account for the "weird leakage"

    the problems of build stuff when tired and thinking you can remember stuff without the spec sheet to hand!

    I'll give it another go later when I'm home and update

    Thanks!



    •   AltAdvertisment

        
       

  4. #4
    Advanced Member level 5
    Points: 9,518, Level: 23
    d123's Avatar
    Join Date
    Jun 2015
    Posts
    1,679
    Helped
    396 / 396
    Points
    9,518
    Level
    23

    Re: High Power LED "function" controller

    Okay, good luck.



    •   AltAdvertisment

        
       

  5. #5
    Newbie level 3
    Points: 28, Level: 1

    Join Date
    Apr 2019
    Posts
    3
    Helped
    0 / 0
    Points
    28
    Level
    1

    Re: High Power LED "function" controller

    So...
    Partial success - once I wired it up correctly!

    Schematic:

    Click image for larger version. 

Name:	plif v1.png 
Views:	8 
Size:	35.4 KB 
ID:	152438

    [found at: systemwizard. co.uk/ images/ plif%20v1. png]

    whilst it works it's not great

    When SW1 is activated (it's a vibration switch) the "flash" is very short, I need some way of making it dwell for longer, this should also help keep Q1 turned off

    SW2-7 these are actually jumpers to allow the user to change which LEDs are activated at each stage.

    The LED is a 3x3W RGB LED

    Any suggestions on how to make this work better, whilst keeping the component count low?
    Last edited by BradtheRad; 18th April 2019 at 10:35. Reason: Image converted to Edaboard attachment



  6. #6
    Advanced Member level 5
    Points: 9,518, Level: 23
    d123's Avatar
    Join Date
    Jun 2015
    Posts
    1,679
    Helped
    396 / 396
    Points
    9,518
    Level
    23

    Re: High Power LED "function" controller

    Hi,

    Keeping component count low might exclude a monostable 555 controlled via the reset pin or an inverter on pin 2 or similar one-shot configurable device. A series RC combination in parallel to the diode/PNP base/resistor line would delay turn-off but it would presumably also delay turn-on...



  7. #7
    Super Moderator
    Points: 51,488, Level: 55

    Join Date
    Apr 2011
    Location
    Minneapolis, Minnesota, USA
    Posts
    12,638
    Helped
    2513 / 2513
    Points
    51,488
    Level
    55

    Re: High Power LED "function" controller

    Simulation showing how a diode-capacitor-resistor network extends a pulse.

    One works on an upward-going pulse.
    The other works on a downward-going pulse.

    Click image for larger version. 

Name:	DCR pulse extenders one going upward other going downward.png 
Views:	4 
Size:	36.7 KB 
ID:	152460

    You may be able to adapt this concept for your purposes.
    Adjust for desired operation via the potentiometer (50k ohm).



    •   AltAdvertisment

        
       

  8. #8
    Advanced Member level 5
    Points: 16,073, Level: 30

    Join Date
    Nov 2012
    Posts
    2,950
    Helped
    709 / 709
    Points
    16,073
    Level
    30

    Re: High Power LED "function" controller

    For a good turn on/off, you should put the LEDs on the collector side, so that the base gets sufficient voltage/current.



  9. #9
    Advanced Member level 5
    Points: 9,518, Level: 23
    d123's Avatar
    Join Date
    Jun 2015
    Posts
    1,679
    Helped
    396 / 396
    Points
    9,518
    Level
    23

    Re: High Power LED "function" controller

    Hi,

    For a longer LED on, an opportunely placed capacitor (capacitance = time) might be all you need.

    To be honest, I had difficulty getting the schematic you posted to function in a simulator, and those diodes into the base of the NPNs confuses me a little, no idea why it didn't operate correctly in the sim 'though, you say it works and it must do, so, to save a little time I simulated a circuit I knew would turn on and off - one extra NPN BJT in there - and as you can see, theoretically the capacitor on the PNP base adds the delay you want without having to place a voltage "stealing" component in front of the LED. The schematic shows 100nF so as to fit the simulation into 1 second, A 1uF capacitor took about 5 seconds or more to turn off the PNP, and as a consequence we'd hope the LED too. Probably real world capacitor value would need testing and tweaking somewhat. Hope the idea is of practical use.

    Click image for larger version. 

Name:	longer on LED circuit thread.JPG 
Views:	3 
Size:	138.2 KB 
ID:	152466



--[[ ]]--