Voltage Reg 0v-10v input with 0v-4.5v output 2A

Discussion in 'Power Electronics' started by JKbiz, Mar 20, 2017.

  1. JKbiz

    Thread Starter New Member

    Mar 20, 2017
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    Hey,

    New to the forum and electronics in general. I am trying to find a variable voltage regulator that will take a standard 0v-10v analog dimming input and output at 0v-4.5v dc.

    Any help would be greatly appreciated!

    Thanks,
    Josh
     
  2. crutschow

    Expert

    Mar 14, 2008
    15,102
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    What's your supply voltage?
    Where is the dimming signal coming from?
     
  3. JKbiz

    Thread Starter New Member

    Mar 20, 2017
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    0
    Dimmer signal is coming from an ETC (electonic theater controls) responce pack. I think 0-10 @ 10mA. Supply voltage is preferably 12vdc but I can spec others if there's a reg. that required it.
     
  4. JKbiz

    Thread Starter New Member

    Mar 20, 2017
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    I could also make it work with a 12v PWM to analog converter as long as the output specs are the same.
     
  5. #12

    Expert

    Nov 30, 2010
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    All I can make out so far is this: voltage scaling.png
     
  6. JKbiz

    Thread Starter New Member

    Mar 20, 2017
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    The divider is on the money voltage wise, I just don't have the current required on the load side.
     
  7. crutschow

    Expert

    Mar 14, 2008
    15,102
    3,954
    He mentioned 2A output in the title.
     
  8. #12

    Expert

    Nov 30, 2010
    17,541
    8,504
    Missed it that time.:D
    Looks like we need a voltage follower with a big transistor to deliver 2 amps.
     
  9. crutschow

    Expert

    Mar 14, 2008
    15,102
    3,954
    What does the 2A load consist of?
     
  10. JKbiz

    Thread Starter New Member

    Mar 20, 2017
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    It is a 3W (so legitimately .6 and change amps) LED element. I may need to run 2 at once so I had the extra amperage for overhead. If I tweak the plan I can, in all fairness, get away with a 1A load.

    It's going to be seen on a camera so I can't get away with the slow PWM driver that it comes with.
     
  11. #12

    Expert

    Nov 30, 2010
    17,541
    8,504
    Maybe a P-mos pull down or a double invert in bipolar?
     
  12. crutschow

    Expert

    Mar 14, 2008
    15,102
    3,954
    Since it's an LED element then it should be completely off at 2V or less.
    This means you could use an LM317 regulator to provide the output, as it goes down to <1.3V minimum.
    It will output up to about 1.5A, and also provides short-circuit, and over-temperature protection.

    Below is the LTspice simulation of that.
    Note that at 1A the LM317 can be dissipating up to about 10W, so it needs to be on an appropriate heatsink.

    upload_2017-3-20_16-43-7.png
     
    Last edited: Mar 20, 2017
  13. JKbiz

    Thread Starter New Member

    Mar 20, 2017
    14
    0
    Brilliant!! Thanks all. Looking at this sim graph I think I'm shopping for a LM317. I'll post once I have this one built and we'll see how she looks on camera.

    Thanks again,
    Josh
     
  14. JKbiz

    Thread Starter New Member

    Mar 20, 2017
    14
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    Update:

    I built this circuit per the diagram but must have missed something as my output voltage doesn't quite match the graph indication.
    Tested Voltage.jpg
     
  15. Kjeldgaard

    Member

    Apr 7, 2016
    182
    60
    Do you have a load on the output of the LM317?

    Minimum output current is 10 mA for the LM317.
    So when the output voltage is to be down to 1.25 V, there must be 120 Ω load and at least 1/4 Watt.
     
  16. JKbiz

    Thread Starter New Member

    Mar 20, 2017
    14
    0
    Fantastic! Solved it straight away!

    Thank you!
     
  17. crutschow

    Expert

    Mar 14, 2008
    15,102
    3,954
    Typically there's a 120Ω resistor between the output and the ADJ pin, which takes care of the minimum load current requirement if there's no other load, but since you were driving a fixed load of LEDs I didn't think it was necessary.
     
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