problem with H-BRIDGE

Discussion in 'The Projects Forum' started by davis103, Jul 7, 2008.

  1. davis103

    Thread Starter Member

    Jun 9, 2008
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    Hi everybody:

    I have implemented the circuit found in the following link:

    http://www.robotroom.com/HBridge.html

    for the motor I am using a linear actuator which involves a dc motor rated at 12 vdc. When the linear actuator is functioning, it does not seem to operate fast enough having no load on the actuator (about 1 amp).

    The TC4424 gets very hot after a couple of seconds of the linear actuator operation and i have to disconnected immediately to prevent the chip from damaging. This does not seem to be right since the chip is being operated at 1 amp and it is rated to be capable to operate to a mamximum of 3 amps. Does anybody know why is this happening?

    I think the chip should be operating normaly since the actuator is draw such a small current ?
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    It's 1.5A per channel; the 3A rating is the total for both channels. You're running the IC at 2/3 capacity.

    Did you connect the exposed pad of the TC4424 to a heat sink or a good sized ground plane?

    What are you driving the TC4424 with?
     
  3. davis103

    Thread Starter Member

    Jun 9, 2008
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    I am not familiar with the heat sink part you mentioned. I am assuming you are asking if i connected it with a good ground. Yes i did connected the chip to the power supply's ground.

    This how i simulated it:

    I am using three power supplies (one for my logic high, second one for my logic low and third one for the 12vdc motor supply).
    when i get a logic high at pin 2 and a logic low at pin 4 then my out A(pin 7) gives me 12 volts with respect to ground (here it is where i introduced the actuator).
    It is good to note that i simulated everithing with out the diodes and capacitors since they are just protecting from undevoltage and noice respectively.

    What am i doing wrong
     
  4. davis103

    Thread Starter Member

    Jun 9, 2008
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    it is also good to note that these are all simulations since the TC4424 will be driven by a microcontroller (PIC)
     
  5. davis103

    Thread Starter Member

    Jun 9, 2008
    27
    0
    If this chip is only 1.5 amps per channel. I do not think it would work. I want to control the actuator's motor direction. I think the best way to do so is with an H-bridge. Does anybody know any H- bridge that can handle 4 to 5 amps at 12 volts continuosly when there is a load (using a microcontroller)?
     
  6. NM2008

    Senior Member

    Feb 9, 2008
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  7. davis103

    Thread Starter Member

    Jun 9, 2008
    27
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    I think there has to be an H bridge IC out there with the desired ratings. This is complecated and i have little time.

    Thanks anyway this is very helpful
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    Well, usually when you're dealing with higher power circuits, you start building the H-bridges out of discrete components.

    The problem with the small components is that there simply isn't enough surface area to dissipate the heat.

    Now if you look at discrete MOSFET devices, you'll find plenty that'll handle your load. Look up IRFZ24's; four of them plus a driver IC should get you going. Don't forget to use heatsinks.

    You COULD use several of those TC4424 devices in parallel - but you'll still need to leave a good-sized area of the board copper clad, and use heatsink compound on the metal plate that's exposed on the underside of the IC to make good heat transfer possible. If the bottom of the IC doesn't touch the copper on the board, you'll need to solder some copper flat stock to the board underneat it in order to ensure it has a heat sink.

    I'm really surprised that it doesn't give a recommended mounting pattern in the datasheet. Have a look at the attached, it's a portion of ST Microelectronics' L6205 datasheet that discusses various methods of mounting such IC's that deal with large amounts of current. For more info, go to ST Microelectronics' site and download the datasheet - too large to attach here.
     
  9. beenthere

    Retired Moderator

    Apr 20, 2004
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    Check the site for the IC warning - the TC4424 is overpowered at 150 ma. You will have to add external components as it is not meant to drive motors directly (or so says the directions).
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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  11. hunt4it44

    New Member

    Aug 4, 2008
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    in the original post by Davis103, it mentions he has built the circuit found at http://www.robotroom.com/HBridge.html . when you click on that link, it mentions the limit of the TC4424 and says to "Check out Figure 10-13 and Figure 10-15 on pages 186 and 187 of Intermediate Robot Building" to drive some "real power".

    does anyone know how to get to "figure 10-13 and 10-15" or perhaps has examples of the schematics themselves?

    thanks.
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    Yes. You follow the link to Amazon.com, and buy the book for $23.09 + shipping.
    It will arrive at your residence in about a week, depending upon the shipping method you select.

    The contents of the book are copyrighted; asking someone to post copies of that on here would be infringement of copyright laws - and such requests are highly frowned upon around here.

    However, there's no reason that the IC in question couldn't be used to drive the gates of other MOSFET devices that have greater current handling capabilities - if you make some provision for "dead time" to prevent "shoot-through".
     
  13. hunt4it44

    New Member

    Aug 4, 2008
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    Regarding the perception of my requesting someone to commit copyright infringement, I have responded via PM directly to SgtWookie.

    yes. it is my intent to use a pwm output from a 16f876a connected to the TC4424 to drive a 12v 10A motor. where I am confused is around the many different schematics showing how this portion of the circuit should be constructed. if anyone has a non-copyrighted example schematic of how to best make a robust mosfet driver circuit, i would appreciate it. Likewise, my interest lies in the function of each component and how they interact. if anyone can point me in a direction where I can advance my understanding of this, I would appreciate it.

    Randy
     
  14. SgtWookie

    Expert

    Jul 17, 2007
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    Actually, there's a much easier approach than trying to build the thing piecemeal. Take a look at the VNH2SP30-E - Automotive Fully Integrated H-Bridge Motor Driver.
    Mouser has them for $10.21 each. Up to 30A output, up to 41Vcc
    http://mouser.com/Search/ProductDetail.aspx?qs=%2bX2uje6VeKVvuwsn%2b4MAoA==

    It will simplify your drive requirements quite a bit - just your PIC, this controller IC, and a connector for your motor and power supply. Just be sure to use the recommended layout pattern for heat dissipation on your board. See pg 19 of the datasheet.
     
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