Low frequency pulse generator

Discussion in 'General Electronics Chat' started by Alexvatt, Dec 19, 2013.

  1. Alexvatt

    Thread Starter Member

    Aug 24, 2013
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    I need a pulse generator to drive a plating cell which has a resistance of roughly 1-2 ohm. I want to drive it with a squire pulses with the frequencies in the range of 1-60Hz and fixed current of 5-10A.
    I want to use Arduino that will drive a MOSFET via octocoupler and a linear regulated 30V, 20A DC power supply. The circuit diagram is attached. Will low resistance of the load be a problem for IPP096N03L MOSFET?

    Thank you for help.
     
  2. wayneh

    Expert

    Sep 9, 2010
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    Here's the OP's circuit.

    [​IMG]
     
  3. wayneh

    Expert

    Sep 9, 2010
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    I'd like to hear an expert opinion on the drain-source breakdown voltage specification of 30V. Since that's the same as the supply voltage, it's a question mark.

    Otherwise it looks OK to me. At 10A load and an on resistance of 8mΩ, power dissipation will be under 1W and well within specifications.
     
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  4. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    The load current is no problem if you mount it to a heatsink. Do not exceed VDS. I would not even work continuously near it.

    If you work with 30V take at one with a VDS of at least. The wires in your circuit are inductances, turning current off can cause unexpected voltage peaks, possibly exceeding 30V.

    The 5V input is negative?
     
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  5. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    It looks like the opto led is the wrong way around.
    You will need negative pulses to have the circuit working
    or turn the led around and use positive pulses.

    Bertus
     
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  6. wayneh

    Expert

    Sep 9, 2010
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    If those values are true, you'll have 30-15A of current when the MOSFET is on, not the 5-10A you mentioned. The PWM can reduce the time-average-current, and perhaps that is what you meant?

    If you're plan is to switch by PWM a 30A load, I'd look for a MOSFET rated to 60A continuous or more. The 35A rating of this one is too scary.
     
  7. Alexvatt

    Thread Starter Member

    Aug 24, 2013
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    I think 5V is positive
     
  8. Alexvatt

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    Aug 24, 2013
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    Thank you, Bertus.
    Alex
     
  9. Alexvatt

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    Aug 24, 2013
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    I'm not planning to exceed 10A current in this set up otherwise my load will melt.
     
  10. Alec_t

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    Sep 17, 2013
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    30V supply, 2 Ohm load = 15A !
    Do you really need 30V?
     
  11. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Perhaps the OP intends to have the mean value of the pulsed load current no more than 10A - rather than the instantaneous peak current.
     
  12. Alexvatt

    Thread Starter Member

    Aug 24, 2013
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    I don't need 30V to get 10A, but 30V is max voltage. The power source that I can get and that is reasonably cheap has a variable voltage and current output so I can set it to 10A.
     
  13. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    A plating cell will have a changing resistance based on temperature and the object being plated.

    You would benefit a lot from using a constant current pulse (not a constant voltage pulse), so plating would be more reliable and repeatable.
     
  14. ronv

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    Nov 12, 2008
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  15. wayneh

    Expert

    Sep 9, 2010
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    Although you may not intend to ever max out the dial on the power supply, I think it would be prudent to design (choose a MOSFET) for that worst case. Murphy's law ensures it WILL happen otherwise. A fuse to protect the MOSFET and the plater is a good idea.
     
  16. Alexvatt

    Thread Starter Member

    Aug 24, 2013
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    I'm using a current source.
     
  17. Alexvatt

    Thread Starter Member

    Aug 24, 2013
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  18. Alexvatt

    Thread Starter Member

    Aug 24, 2013
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    It makes sense I will likely eventually need a larger current and more powerful source.
     
  19. THE_RB

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    Your circuit won't work with a current source, because you need a voltage source of a fixed voltage or >X voltage to operate the opto and the FET gate.

    If you did intend that the plating power comes from a current source, then you need to specify that the control circuit of opto and FET gate is powered from a separate voltage source. :)
     
  20. ronv

    AAC Fanatic!

    Nov 12, 2008
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    I think we thought you were using a 30 volt supply so it would have about 15 volts of gate drive. But if you are gong to use a constant current source all bets are off if the current is set to low. But, that begs the question of why do you need PWM if you can adjust the current and voltage already?
     
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