0-10VDC dimmer control

Discussion in 'General Electronics Chat' started by mcgyvr, Jun 17, 2010.

  1. mcgyvr

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    Is this a good circuit to use for the 0-10V dimmer control for an LED project I'm working on. Any suggestions..additions,etc... Supply is a 12V typical wall wart. I will probably be powering some 12V fans from the output of the fuse too.
     
  2. R!f@@

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    You cannot dim led's efficiently that way, but u can control fan's
    To dim LED's, u have to use PWM
     
  3. SgtWookie

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    Jul 17, 2007
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    An LM317 output won't go to 0v; roughly 1.2v to 1.3v is as low as it'll get unless you have a negative supply handy.

    Your D1 doesn't do anything.

    LEDs need to be regulated by current, not voltage.
     
  4. kingdano

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    Apr 14, 2010
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    my only point is that D1 is suggested in the datasheet for the 317 device to protect the device when being used to drive a reactive load.

    im not 100 percent sure, but i just read through the datasheet and thought they mentioned using diodes from OUT to ADJ and IN to OUT as well.

    let me see if i can track it down
     
  5. kingdano

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    on the national semi version of the device - the LM117.pdf datasheet - page 10.

    When external capacitors are used with any IC regulator it is sometimes necessary to add protection diodes to prevent the capacitors from discharging through low current points into the regulator. Most 10 μF capacitors have low enough internal series resistance to deliver 20A spikes when shorted. Although
    the surge is short, there is enough energy to damage parts of the IC. When an output capacitor is connected to a regulator and the input is shorted, the output capacitor will discharge into the output of the regulator. The discharge current depends on the value of the capacitor, the output voltage of the regulator, and the rate of decrease of VIN. In the LM117, this discharge path
    is through a large junction that is able to sustain 15A surge with no problem. This is not true of other types of positive regulators. For output capacitors of 25 μF or less, there is no need to use diodes. The bypass capacitor on the adjustment terminal can discharge through a low current junction. Discharge occurs when either the input, or the output, is shorted. Internal to the LM117
    is a 50Ω resistor which limits the peak discharge current. No protection is needed for output voltages of 25V or less and 10 μF capacitance. Figure 3 shows an LM117 with protection diodes included for use with outputs greater than 25V and high values of output capacitance
     
  6. mcgyvr

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    Sorry... I did not provide the correct information about the use of this circuit.. This is simply the 0 (or whatever is lowest) to 10VDC signal to the Meanwell constant current driver that I am using to power the LED's.. The ballast simply accepts 0-10V to control the output current. I'm really not worried about it going all the way down to 0V as I will not be dimming them that low anyways so 2-10V is fine.
    Per Nationals datasheet D1 protects the LM317 from any discharge currents from the cap.
     
  7. mcgyvr

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  8. kingdano

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    if you are going to cite the datasheet, do so properly and use both protection diodes or neither.

    in this case (output capacitance < 25uF) neither is suggested for use.

    if you want to be safe and include one, include both or it defeats the purpose entirely.

    the other diode should be connected between IN and OUT (cathode to IN)
     
  9. kingdano

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    Apr 14, 2010
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    reagrding your circuit

    R1 (150 Ω) should not be a potentiometer and R2 (i assume intended to be a 1kΩ potentiometer) is not drawn correctly on the schematic to function as a variable resistor.

    you need to connect the wiper leg of the pot to the upper node of the resistor where the 150Ω resistor meets the 1kΩ pot.

    you also need an input capacitor (0.1 uF per the datasheet im almost 100% positive) and a smaller value output capacitor (0.1 uF would be fine) in addition to (read: in parallel with) your 25 uF cap.

    these will help greatly with "cleaning up" the voltages coming into and going out from the device.
     
  10. mcgyvr

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    My plan was to simply use R1 as a pot to allow me to dial in the voltage to ensure I can turn R2 all the way down or up and not exceed my 10V requirement then I will simply glue R1 in place to set it's resistance (probably 150 ohm) for ever.
    As far as the drawing being incorrect for the pots that is how circuit maker student has them in the library.
     
  11. mcgyvr

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    Is this better
     
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