DC-DC converter

Discussion in 'The Projects Forum' started by philm01, Aug 12, 2014.

  1. philm01

    Thread Starter Member

    Mar 22, 2014
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    Hello everyone,

    I am working on a project which I need some help on. Basically, I am designing a DC-DC Converter which is to be controlled via a micro-controller PWM signal. The input will be 12 V power and the output will be variable 1 - 12 V (corresponding to the frequency of the PWM signal)

    I was looking at buck converter but I am not sure if that is the correct route to go because I will be using a maximum of 10 Arms.

    So I wanted to turn to the community to get the opinion of more experienced designs.

    So my question is this, what is the best circuit that I can design for this project? Again, I was looking at buck converters but I am not sure if there is a better or different circuit that I can use.
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Does the output voltage need to be regulated (i.e. basically independent of any variations in output load)? If so you will need voltage feedback from the output to control the PWM duty-cycle.
     
    Last edited: Aug 12, 2014
  3. philm01

    Thread Starter Member

    Mar 22, 2014
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    Yes, although, I will have the circuitry for that. Again everything will need to be controlled via microcontroller.

    It will need to be a constant voltage source (constant as in, if I set it to 5 V, it will remain at 5 V no matter what I do)
     
  4. philm01

    Thread Starter Member

    Mar 22, 2014
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    Is there a circuit that you recommend for me to use?
     
  5. crutschow

    Expert

    Mar 14, 2008
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    You show me yours and I'll show you mine. ;) I can't determine what you need without seeing your circuit. Post the "circuitry for that" that you have.
     
  6. philm01

    Thread Starter Member

    Mar 22, 2014
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    Ok...... But to let you know, the circuit that I am about to post is a little weird and may not necessarily be a typical way of doing somethings. But, to give you some background, the circuit that am building creates high voltage for breaking water up into its base components. Please note, you have been warned.

    So J1 goes to a capacitor filled with water to create hydrogen gas and the FET is controlled by a microcontroller. The +12 represents my input to the circuit
     
  7. philm01

    Thread Starter Member

    Mar 22, 2014
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    So forgive my ignorance, but wouldn't a buck converter work?

    I mean, I would have to modify the duty cycle which is perfectly fine by me since this is controlled by a microcontroller.
     
  8. Brownout

    Well-Known Member

    Jan 10, 2012
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    I hear a mod a'comin'
     
  9. philm01

    Thread Starter Member

    Mar 22, 2014
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    Why is that?

    I want to check with the community that am designing everything right. Plus, I would like to have their feedback on what they would do.

    So I am looking into making a buck converter and I have a few simulations but I am working on an understanding of what they are.

    Please, if anyone has an better ideas, then feel free to share
     
  10. philm01

    Thread Starter Member

    Mar 22, 2014
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    oK, so I kinda cheated. I ran the simulator with a switch. Then, when I replaced the switch with the MOSFET, the voltage was unable to cycle between the range I needed it to. With the switch, I could sweep between 0 and 12 V. With the MOSFET, I can only sweep between 0 - 2 V.

    Darn
     
  11. crutschow

    Expert

    Mar 14, 2008
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    A buck converter will work but it will need voltage feedback from the output to the microcontroller input if you want a regulated output and there will need to be a compensation network in the feedback to stabilize the loop.

    Post the schematic for the circuit you simulated that didn't work.
     
  12. Shagas

    Active Member

    May 13, 2013
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    I also happen to require a DC-DC to drive a heavy load and while I'm experimenting on how to make one , I've waiting on this one :) Hope it's not a fake.
     
  13. philm01

    Thread Starter Member

    Mar 22, 2014
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    Well again, it is like super simple. I was only using default values and parts. Nothing too complex.

    I was driving it with 2KHz. So I was driving at 100% duty cycle which I would think that Vout = Vin at that point.
     
  14. ronv

    AAC Fanatic!

    Nov 12, 2008
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    You are using an NFET in a source follower mode. The source will only go to the gate voltage minus the gate threshold voltage - in your case a couple of volts. You either need to drive the gate with a voltage of about 20 or 22 volts or use a PFET and make a small driver to interface your micro to the 12 volts.
     
  15. philm01

    Thread Starter Member

    Mar 22, 2014
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    Ok. Sadly, I will not have access to 20 or 22 volts. I guess I could make a boost converter and have the microcontroller drive a transistor that will drive the FET at 22 volts (darlington pair) but that might be a little impractical. Then again, they do make boost converter chips and they have app notes and everything. I will keep that in my options.

    But as for the second option. Are you saying switch out the N-Channel with a p-Channel? If that is the case, sweet. I will try that. (Please note that the values you see here in the circuit and not the final values for my circuit, I am trying to find out what is best right now!)

    Yeah, I was never intending to drive a MOSFET directly with the controller. I know that that is a bad idea (unless I am using a 2N7000). I was going to be using a driver chip for whatever I use. I just do not have it in the simulation
     
  16. crutschow

    Expert

    Mar 14, 2008
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    Yes, but note that with a P-MOSFET the source goes to the V+ supply and the drain is the output to the inductor.
     
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