+ Post New Thread
Results 1 to 9 of 9
  1. #1
    Newbie level 6
    Points: 398, Level: 4

    Join Date
    Mar 2017
    Posts
    11
    Helped
    0 / 0
    Points
    398
    Level
    4

    Output inverter bridge for welding TIG machine?

    I have TIG weding machne , but only DC and need AC for welding aluminium and pulse for any precise works.
    My idea is add on output full bridge for chnging polarity and or make pulse.

    Technical
    current is 150A max
    switching frequency 400Hz max

    As transistor in to bridge I think IPT012N08N5 80V 300A 1,2mOhm, for controlling bridge any MCU STM32F3 with full bridge PWM

    I'm looking for a suitable driver for High and low side MOSFET , for charging 13nF input gate capacitor.
    Do you recommend suitable drivers with sufficient current?

  2. #2
    Advanced Member level 4
    Points: 6,997, Level: 19

    Join Date
    Dec 2015
    Location
    Madrid, Spain
    Posts
    1,235
    Helped
    303 / 303
    Points
    6,997
    Level
    19

    Re: Output inverter bridge for welding TIG machine?

    Do you recommend suitable drivers with sufficient current?
    Switching freq is 400 Hz, so any driver will work.



    •   AltAdvertisment

        
       

  3. #3
    Full Member level 5
    Points: 2,313, Level: 11

    Join Date
    Jul 2012
    Posts
    246
    Helped
    18 / 18
    Points
    2,313
    Level
    11

    Re: Output inverter bridge for welding TIG machine?

    It will be, on the other hand, switching current is 150A, Qoss 208nC and no-load voltage may be 50V. For mimimising switching lost we need mimimise switching time
    if we want to open transistor on 40ns we need more than 5A driver current.
    For example 6A driver for low side is not problém, but 6A driver for high side with transformerles desig may is problém.



  4. #4
    Newbie level 6
    Points: 398, Level: 4

    Join Date
    Mar 2017
    Posts
    11
    Helped
    0 / 0
    Points
    398
    Level
    4

    Re: Output inverter bridge for welding TIG machine?

    In DC mode the bridge must be in "static state" and this eliminates a simple transformers MOSFET driver.
    May be I use full isolated digital driver with DC/DC PS.

    Yes max switching spoeed is 400Hz , but current is 150A and becouse trnsoisto have SMD HSOF case I will have to invent a PCB that will transfer 150A.



    •   AltAdvertisment

        
       

  5. #5
    Super Moderator
    Points: 250,799, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    43,661
    Helped
    13280 / 13280
    Points
    250,799
    Level
    100

    Re: Output inverter bridge for welding TIG machine?

    You should start to design the transistor heat sinking. 150 A (27 W conduction losses in static operation) won't work on any kind of regular PCB. I guess, you better switch to conventional transistor packages.



  6. #6
    Member level 1
    Points: 534, Level: 4

    Join Date
    Feb 2017
    Posts
    35
    Helped
    0 / 0
    Points
    534
    Level
    4

    Re: Output inverter bridge for welding TIG machine?

    On the bridge it is even 2 * 27W, but I thing it is not problem , yes must be used heatsink and fan.



  7. #7
    Newbie level 6
    Points: 398, Level: 4

    Join Date
    Mar 2017
    Posts
    11
    Helped
    0 / 0
    Points
    398
    Level
    4

    Re: Output inverter bridge for welding TIG machine?

    For clarification. conductivity losses can be reduced by using a pair of transistors 8pcs in full bridge. The question is whether it is economic, because 57W is only 1,5% of total power.
    Cool the transistors is nit problem, this make old PC CPU heatsing.
    I see the bigger problem in PCB losses. at least on cheap 70um pcb from china, may be add an soldem 0.3mm copper foil



    •   AltAdvertisment

        
       

  8. #8
    Super Moderator
    Points: 250,799, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    43,661
    Helped
    13280 / 13280
    Points
    250,799
    Level
    100

    Re: Output inverter bridge for welding TIG machine?

    conductivity losses can be reduced by using a pair of transistors 8pcs in full bridge.
    That's an option. It's still rather difficult to interface the SMD transistor package to a heatsink. You can e.g. use massive thermal vias and mount the PCB on top of the heatsink.

    Besides special thick copper designs, multilayer stack-ups with many (e.g. 6 or 8) 70 um layers are an effective way to make high current PCB.

    I wonder if screw amounted MOSFET modules and copper bars are a more simple solution in this case.



  9. #9
    Newbie level 6
    Points: 398, Level: 4

    Join Date
    Mar 2017
    Posts
    11
    Helped
    0 / 0
    Points
    398
    Level
    4

    Re: Output inverter bridge for welding TIG machine?

    I played with a PCB layout and her is my first design in early alfa version.
    I remember, I do not want to produce it in big but in a few pieces
    Motherboiard is FR4 with 70um coper, on golden surfaces it is soldered aditional 0,3mm coper foil.
    Center rectngle is 40x20mm on top i.e. resistance approximately under 100u Ohm, the same is on Bottom side.
    MOSFET 2x IAUT300N08S5N012 i.e. typical Rdson on pair 500uOhm.
    As connector on every ports 2x brass screw 4 or 5mm with 2pcs oring connector on every screw.
    Transistors will of course have a heatsing and a fan.

    What do you think?

    .Click image for larger version. 

Name:	TIG.png 
Views:	2 
Size:	124.0 KB 
ID:	150774



--[[ ]]--