variable 0-5 volt milliamp input to a high amperage variable 0-5 vdc output

Discussion in 'Analog & Mixed-Signal Design' started by BobW55, Feb 13, 2019.

  1. BobW55

    Thread Starter Active Member

    Jul 22, 2008
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    I am building a laser engraver, the current setup uses a 12vdc buck to drop to 5 vdc @ about 6 amps.
    It uses a IRFZ44n to switch on/off the 12 vdc input to the buck.
    I want to use a variable input 0-5vdc I am sure only a few milliamps, to be able to vary the laser power by varying the buck 5 vdc output
    I have been searching like crazy but not finding anything premade that I am aware of.
    Can you suggest anything ready made, or suggest where i might go to read up about building my own.
     
    Last edited: Feb 14, 2019
  2. dendad

    Distinguished Member

    Feb 20, 2016
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  3. sghioto

    Well-Known Member

    Dec 31, 2017
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    So you want a circuit or pre-made board that will PWM the IRFZ44n by using a variable 0 to 5 volt source?
    SG
     
  4. BR-549

    AAC Fanatic!

    Sep 22, 2013
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    I don't understand what you are saying and asking.
     
  5. ElectricSpidey

    Active Member

    Dec 2, 2017
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    Sounds like something you could do with a pot (voltage divider) and a power transistor configured as common collector. If your 0-5 volts is coming from some signal source, you can add an Op-Amp

    The wasted wattage wouldn’t be too bad, probably about 8 watts or so when set at half power.

    You would lose about .7 volts or so on the output…

    As far as keeping the output purely from the buck, and getting a variable output…well that’s a little above my pay grade on an online forum, but I’m sure somebody with more experience with that sort of thing can help.
     
  6. sghioto

    Well-Known Member

    Dec 31, 2017
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    Now I'm thinking using the IRFN44n switching the ground on the laser engraver using a 555.
    SG
    EEE engraver driver.PNG
     
  7. BobW55

    Thread Starter Active Member

    Jul 22, 2008
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    The current set up uses the IRFZ44n as a on/off switch to the 12 volt input to the buck. The buck has a pot to set the output voltage and current.
    Right now I can only vary the time the laser is on/off (PWM) via a variable 0-5vdc from the controller (Spark Concepts CNC ver4)
    when the board with the IRFZ44N sees about 0.6 volts it turns on. There is a small opto isolator board with a 12 vdc input that the IRFZ44N is mounted on.
    I thought about adding an external resistor to the voltage control pot on the buck, but when you start adding voltage, the output of the buck drops. I want it to increase. Yea I could use an inverter on that input. I just thought maybe someone knew of a ready made buck that has an external voltage control.
    That one you linked to is similar to what I have, but the TTL/PWM control is built into it.
    I'm still searching.
     
  8. sghioto

    Well-Known Member

    Dec 31, 2017
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    If you want more voltage why not just forget the buck and PWM the 12 volt supply directly to the engraver?
    SG
     
  9. BobW55

    Thread Starter Active Member

    Jul 22, 2008
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    I have no PWM output from the controller. It varies the output from 0-5 volts, (0%= 0 volts 100%=5 volts) I need that to vary the voltage to the laser from about 3.5 to 5 volts max. @ 4 amps ( 10 watt laser @ 5 volts about 2 amps but I like overhead)
    May have to use a microprocessor (PIC) and just make a PWM output
     
  10. sghioto

    Well-Known Member

    Dec 31, 2017
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