Potentiometer for LED Dimming

Discussion in 'General Electronics Chat' started by mpangrekar, Jun 9, 2009.

  1. mpangrekar

    Thread Starter Member

    May 16, 2009
    14
    0
    Hi,

    Earlier I had posted a question about dimming MR16 LED.

    Now, I am trying to figure out if I can dim this MR16 LED bulb with a potentiometer (attached is datasheet for bulb, potentiometer info below).

    This bulb has two pins that accept 2V to 15V AC/DC. I have 12 VDC @ 1 Amp input supply available to give to this LED bulb. I found Honeywell potentiometer rated for 4 Watts and the LED bulb that I want to dim is also rated for 4 Watts. If I hook up this pot between 12V & LED bulb could it work?

    Second question: How do I figure out what resistance to select for the pot. Just as a trial & error, I tried a 1/4 Watts pot with 1M Ohm resistance (audio taper) and there was almost no dimming, I got 0% to 100% dimming in 10 degrees rotation of the knob.

    HONEYWELL 58 Series Industrial Potentiometer, Wire Wound Element, Solder lug Terminals, 4 W Power Rating, 5 kOhm Resistance Value
    [​IMG]

    Product SpecificationsPotentiometer
    TypeIndustrial Element TypeWire
    WoundTerminal Solder lug
    Power Rating4 W
    Resistance Value5 kOhmResistance
    Tolerance±5 %Linearity±2 %

    Bushing Thread9,53 mm [0.375 in] x 32 NEF-2ABushing Length9,53 mm [0.375 in]Bushing TypeStandardShaft Diameter6,35 mm [0.25 in]Shaft Length50,80 mm [2.0 in]Shaft EndingPlain roundBody42.93 mm [1.69 in] diameter, ± 0.79 mm [0.031 in], except at terminal standoffElectrical TaperLinearOperating Temperature-55 °C to 105 °C [-67 °F to 220 °F]Working Voltage (Max.)350 VRotational Life25000 cyclesMechanical Rotation300°AvailabilityGlobalSeries Name58UNSPSC Code4111363300UNSPSC Commodity4111363300 Potentiometers

    Thanks.

    Mayur
     
  2. bertus

    Administrator

    Apr 5, 2008
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  3. mpangrekar

    Thread Starter Member

    May 16, 2009
    14
    0
    Hello,

    Thanks for your reply. Most of the times, I am using DC, but sometimes I do use AC. The potential problem with using a PWM circuit is: the LED dimmable bulb that I am trying to dim has a PWM circuit built into it - Could this be a conflict if I use another PWM circuit to dim an LED bulb which has its own PWM? (In this case, Circuit will look like this: 12V DC supply goes to - a PWM circuit goes to - another PWM circuit goes to - LED dimmable bulb --> conflict?)?

    Also, what is the best way to determine Ohm for a potentiometer?

    Mayur
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,648
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    Hello,

    From the datasheet I can not find that it has a build in pwm circuit.
    I also can not find the voltage range of 2 - 12 Volts.
    I think that you can use the pwm circuit to dimm it.

    Greetings,
    Bertus
     
  5. mpangrekar

    Thread Starter Member

    May 16, 2009
    14
    0
    Thanks for your reply. The mfgr Ushio told me that it has PWM circuit built into it, they cannot give any more info on that because it is proprietary. Attached find dimming tested by Ushio.

    Any more thoughts?

    Mayur
     
  6. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,346
    Hello,

    The curve you show is like a voltage regulation.
    If the applied voltage changes from 5 to 8 volts the led goes from almost no light to full brightness.
    It looks like a two leds in series with a current regulator (that does not work correctly below 8 Volts). (each led is about 3.5 Volts).

    Greetings,
    Bertus
     
    Last edited: Jun 11, 2009
  7. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,172
    397
    I would use a 50Ω , 4W pot connected across power supply, LED wiper to common. Could add a resistor from top of pot to supply[22 to 33] , same on bottom to make pot active over most of its travel.
     
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