H bridge [Schematic included ] loading problems

Discussion in 'The Projects Forum' started by thekaiser11234, Jul 5, 2012.

  1. thekaiser11234

    Thread Starter New Member

    Apr 29, 2012
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    Hello i have been working on h bridge for awhile its my 1st design as you see below

    using it to control 14amp rater 24 volt (250 watt) motor

    controlling using Arduino (500hz frequency )

    (1-0) move in 1 direction
    (0-1) other direction
    (1-1) Break

    the upper side is P channel IRF9540 or 9540N i used both
    http://www.irf.com/product-info/datasheets/data/irf9540n.pdf

    the lower side is N channel IRF540 or IRF540N also :)
    http://www.irf.com/product-info/datasheets/data/irf540n.pdf

    for level shifting ( 5 to 12v)
    im using BC547 NPN

    http://www.futurlec.com/Datasheet/Transistor/BC547.pdf

    to keep the voltage (VGS and VSG ) for P and N transistors
    im using 12 v zener

    here they name it only by voltage and wattages
    im currently using 1 watt zeners

    the max available is 5 watt

    R zener is 1k in case its not obvious enough !

    the driver works fine without loading
    but if i add them my sort of cart project
    15k load

    the motors dont seem to move the transistor HEAT AND HEAT then they blow !

    can you guide me whats the problem

    sorry for the long post ,just hoping for help asap !

    Thank you to infinity :D
     
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    1. Are you using a fixed deadtime or none at all (relying only on the gate drive circuitry delays) ?
    2. Are the MOSFETs mounted on heatsinks?
    3. "load 15k". does that mean 15kOhm?

    4. battery voltage is 24V?


    PS: please use points at the intersections where a electric connection between lines is.
     
  3. thekaiser11234

    Thread Starter New Member

    Apr 29, 2012
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    1. Are you using a fixed deadtime or none at all (relying only on the gate drive circuitry delays) ?
    i dont seem to understand totally what you mean
    please clarify


    2 Mosfets are mounted on heat sinks yes

    3. sorry i mean loading the motors with 15kg load sorry for confusion

    4. battery voltage is 24V yes !

    thanks for the hint i will do this later
    is any thing else not obvious in the circuit ?
     
  4. mhastie1234

    New Member

    Feb 10, 2012
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    Change 10k base resistor to 1k. Your not saturating the transistor. You should also put diodes across drain and source of your mosfet.
     
  5. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    1. What is the sequence of IN1, IN2? Is there a time when both are off?

    3. What does that mean in terms of motor current?
     
  6. thekaiser11234

    Thread Starter New Member

    Apr 29, 2012
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    1- through the code they shall be both on or (one and the other off ) in case of no movement break is activated

    3-well im using 2 motors of the motors included above
    they both consume averagely 20 amp or lil more which is 10 ampere for each motor

    (also i wana ask is it a problem if i let both off the same time ? )
     
  7. thekaiser11234

    Thread Starter New Member

    Apr 29, 2012
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    Thank you for replying

    about the 1k resistor wont this consume more current from my controller ??


    and for the fly back diodes in the datasheets there are body diodes in each fet
    and they can take 20 ampere which isnot available in market here
     
  8. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    20A for a IRF540 is to much IMO. Even if the datasheet says 22A@25°C (or 15A@100°C). You should put more than 1 in parallel. Also you didn't say the size of the heatsink. Did you use thermal compound?

    You are applying 24V battery voltage to the gates of Q4 and Q8 when you want them to turn on.
    The gates of Q6 and Q8 get -22V at their gates (referenced to the source terminal) when turned on. That's too much.

    Example:
    IN2 = 5V
    IN1 = 5V
    Q8 conducts
    Q7 does not conduct

    IN2 = 5V
    IN1 = 0V
    Q8 does not conduct
    Q7 conducts

    Question: Is there a time when both transistors of one leg conduct? This is a short circuit for the battery, however it can be a very short time and maybe the wire inductances from the battery are long enough to limit the current for this short amount of time. The correct thing would be to drive the MOSFETs with gate signals that assure a certain time where both MOSFETs of one leg are OFF (deadtime). I would choose a few us for this application.

    In short:

    - Check if there is cross-conduction.
    - Adjust your gate resistor dividers in order to apply about 15V / -15V to them.
    - Use at least 2 of those MOSFETs in parallel for 20A or use other MOSFETs
     
  9. thekaiser11234

    Thread Starter New Member

    Apr 29, 2012
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    20A for a IRF540 is to much IMO. Even if the datasheet says 22A@25°C (or 15A@100°C). You should put more than 1 in parallel. Also you didn't say the size of the heatsink. Did you use thermal compound?

    thats really what is happening sorry for confusion i made 2 motor drives 1 for each motor so yes they are working in parallel
    about heatsink im using 4 heatsinks 1 for each FET with largest size available
    and if you are talking about that white thingy you put behind the Fet yes im using one


    You are applying 24V battery voltage to the gates of Q4 and Q8 when you want them to turn on.
    The gates of Q6 and Q8 get -22V at their gates (referenced to the source terminal) when turned on. That's too much
    .
    you mean Q4 and Q8 ?
    isnot the zener diodes doing the job to limit the voltage to 12 of gates ( referenced to source ) ?
    am i missing something obvious ?



    about the voltage devision the 10k and 1k resistors and changing them for (15 and -15 ) thingy isnot the zener diode doing the job ?

    or im still missing something ?
     
  10. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Sorry about that, yes you are right. It's partly due to the schematics unusual layout.
     
  11. thekaiser11234

    Thread Starter New Member

    Apr 29, 2012
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    srry for that i promise this wont happen next time :)

    so what do you think the problem is ?
    the frequency ?
    or the FETS aint good enough ??

    or resistor values ??

    or i need higher wattages zener ??



    this is confusing for me as a beginner

    Thanks in advance
     
  12. mhastie1234

    New Member

    Feb 10, 2012
    29
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    You have to put a smaller resistor on the base of the transistor. With a 10k resistor you are not saturating you transistor. With no load it might work fine. Adding a load WILL fry it every time.
     
  13. mhastie1234

    New Member

    Feb 10, 2012
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    Fly back diodes in mosfets are a by product of the manufacturing process. It is good practice to include them.
     
  14. thekaiser11234

    Thread Starter New Member

    Apr 29, 2012
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    can you suggest me a value ? suitable for my bc547 ?
     
  15. thekaiser11234

    Thread Starter New Member

    Apr 29, 2012
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    also how would loading fry them ??

    loading is on fets BC547 is only for lvl shifting
     
  16. thekaiser11234

    Thread Starter New Member

    Apr 29, 2012
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    ok guys im still trying with this circuit

    i tried to decrease the load and see whats gonna happen

    the robot moved

    but too slow the first voltage was about 3 v or something and increases as the motor moving within a noticable speed

    the current drawn is around 5 ampere

    any thoughts ? :S
     
  17. mhastie1234

    New Member

    Feb 10, 2012
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    If you dropped your 10k to 1k on the base. Try removing the 1k resistor on the gate of the mosfet and see if that helps. On the data sheet its 5.1ohm
     
  18. Mhlengi

    New Member

    Sep 28, 2012
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    Hi, I am building an H Bridge to drive a 2A @ 12V motor and I am using a 555 timer for the signal, so I tested the circuit at 7.5V DC but the motor only rotates in one direction, I use a 4.7k variable resistor for controlling the motor and this only makes the motor speed slow when the variable is turned fully anti-clockwise n the speed fast wen the variable is turned fully clockwise. Any suggestions on how I can change the direction.
     
  19. Audioguru

    New Member

    Dec 20, 2007
    9,411
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    Please start your own thread and attach the schematic.
     
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