H-Bridge Motor Control

Discussion in 'General Electronics Chat' started by Phazzer, Nov 10, 2006.

  1. Phazzer

    Thread Starter New Member

    Nov 10, 2006
    3
    0
    Hello all,

    I woroking on my senior design for college and have a question about the H-bridge I've built. The set-up is similar to the one at this link:

    http://www.parallax.com/dl/docs/cols/nv/vol2/col/nv52.pdf

    Changes:
    1) I have a +24V supply running to the top of the h-bridge instead of his power supply.
    2) R1 and R2 are 100k resistors, not 120k
    3) C3 and C4 are 0.033 uF (This is still 10 times the input capacitance of FET and should be fine)
    4) D4-D7 are 13V zeners not 15V (Does not change much of anything)
    5) R4-R7 I had set at 10ohm, and then 51ohm which lead me to my problem, btw these are 1/4W as well.

    Problem:
    I have the HIP4081A and surrounding circuitry running fine. I can use a scope to see the switching on the two Mosfets I need when the Fets are not attached. The gates voltage is +13 above that of the source. When I continue and attatch the Mosfets I keep having one (atleast visable) of the R4-R7 burning up. I know I have to be driving the gates with to much current for this to happen, but even when I increase those resistors I get the same result, toast. Is there any way around this, or maybe I'm doing something else wrong. I've calculated the power for the resistor and it seems like it would be to much any way I go for a 1/4W but I see other H-bridges out there with what seems to be 1/4W resistors. If anyone can help me I would appreciate it. My project is due in 4 weeks and I'm stuck on this part of it. If there is any other information you need to help me just let me know.

    Thank you,
    Anthony
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Phazzar,

    You did not mention whether you were using the HRF3205 as called for in the circuit description.

    Is this the case or have you selected a different MOSFET for your H-bridge?

    hgmjr
     
  3. Phazzer

    Thread Starter New Member

    Nov 10, 2006
    3
    0
    Sorry about that. I'm using OnSemi's NTP18N06G. Hope that helps and thanks for a quick reply.
     
  4. EngineerJoe

    Member

    Nov 4, 2006
    15
    0
    Any luck? With all of those connections, I wonder if the wiring is correct. Are all of your components still OK. Sometimes when something frys, other parts die with them. What is the advantage of using the HIP4081?

    I've used a PIC microcontroller to drive an H-bridge directly but you have to watch out for the time that it takes to turn off the transistors. The T(off) time is usually longer than the T(on) time. I also used the bottom two transistors in the "ON" state to act as a magnetic break for the motor. Timing is very important for an H-bridge!
     
  5. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Phazzar,

    I know you stated in your initial posting that you were able to see 12-13 volt MOSFET drive signals from the HIP4081A using a scope.

    I think you may need to go back and replace your 13 volt zeners with the recommended 15 volt zeners called for in Figure 52.3 of the application note. It sounds to me like the output of the HIP4081 is swinging to a voltage in excess of the zener voltage of 13V. If this is true then it would explain your resistors getting too hot since that would mean that every volt above the zener voltage would be dropped across the series resistor. At 51 ohms these resistors would only need a current of 70 milliamps or so to exceed their 1/4 Watt rating.

    If you can't get your hands on a 15V zener then you can take say 3 or 4 standard diodes in series with the 13V zener to get you past this problem and on to the next one.

    hgmjr
     
  6. Phazzer

    Thread Starter New Member

    Nov 10, 2006
    3
    0
    Hey all,

    I'm ordering 15V zeners as I wirte this, hopefully this will work. I've been in my school lab for the past 6 hours working on this and took the entire Fet system apart than attached just the Ahigh side and Blow side fets. Before running I check the driver circuitry to make sure I was getting my PWM wave out correctly. I attached the fet and driver circuitry and turned on the power. Stupid me forgot to place in zeners back into the circuit :mad: , needless to say the drive took a beating and now the A high output is locked high. I have replacements for it but I was also wondering because both FETs that were attached also went out, there always stuck on. Is this something that the zener missing would cause I know the zener is there to stabalize the voltage on the gate to +15V but wouldn't the b low output have been damaged before the fet? :confused: You guys have been a great help so far and I hope to hear from you soon.

    Anthony
     
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