3 phase motor drive circuit

Discussion in 'General Electronics Chat' started by jeka616, Aug 10, 2009.

  1. jeka616

    Thread Starter Active Member

    Jan 14, 2009
    121
    1
    Hi all.

    Looking for a 3 phase motor drive circuit. Intention is, to run 3 phase brushless motors (ones used in radio controlled aircraft). Commercial ones are made to work with radio transmitter, for speed control, I don't need this. It will run at constant speed.

    I've come across with some drawings here in this forum, but all with PIC microcontroller. Don't need this yet.

    If anyone can provide circuit to run brushless 3 phase motor on DC 10-12v (possible, no?) it wil be highly appreciated.

    THanks all.
     
  2. kkazem

    Active Member

    Jul 23, 2009
    160
    26
    HI,

    Perhaps the easiest way for you to get your motor up and running is to use a 3-phase BDC motor controller IC. STS has many in their catalog and most should be in-stock with perhaps even free samples available, or you can order them in small quantity from Digi-Key. STS stands for SGS Thompson. Actually, they go by ST Microsystems these days. Their website is at: http://www.st.com/stonline/ then use the keyword search for BDC motor controller.

    Allegro Microsystems is another IC manufacturer with many types. Try this link: http://www.allegromicro.com/en/Products/Categories/ICs/motor.asp

    Also, Freescale's MC34929 IC, use this link: http://www.freescale.com/files/anal...ALE&WT_FILE_FORMAT=pdf&WT_ASSET=Documentation

    Theirs is a complete controller and driver in a chip.

    There are others as well. I used this search term on google: "brushless dc motor controller ic" without the quotes, but it might work better with the quotes as it would be treated as a phrase.

    Good luck.

    Regards,
    Kamran Kazem
    kkazem
     
  3. jeka616

    Thread Starter Active Member

    Jan 14, 2009
    121
    1
    Kamran,

    I only found ST L6234. Looks like it has everything built in. Though it says output current up to 5 A, I doubt it...need to figure out to hook up power mosfets to this chip. and not sure if this is possible, as it already has mosfets built in to it. SHoul I just paralel them with power mosfets?

    I need to sit down and designa a circuit for it, unfortunately don't have time. Therefore i asked if any one has already done so, so I can copy the circuit just.

    thx
     
    mbek likes this.
  4. kkazem

    Active Member

    Jul 23, 2009
    160
    26
    Hi,

    Yes, the ST Micro L6234 or the L6235 really can drive 5.6A peak or 2.8A DC and for the size of small motor that I'm assuming you're going to use, it should not need any other power MOSFETs. In order to choose the L6234 versus the L6235, you'll have to look at the datasheets carefully. They are somewhat similar, but the L6235 has more features and can use a switching frequency up to 100KHz whereas the 6234 only goes up to 50KHz. One of them has alaments of a speed control loop built-in and interface to hall effect sensors, if your motor has them.

    Again, despite the small size, they can do the job at up to 52VDC input. How, you ask? Well, there are a few reasons why. First, the power FETs inside have a very low RDSon of only 0.3 OHM, so for a 3-phase H-bridge, there will almost always be 2 power FETs on at any one time. 2.8A continuous DC current squared times 0.6 ohms (0.3 X 2) = 4.7 watts. Since this part has several versions of special surface-mount IC's, if you pick the largest one, and design the PC board with plenty of copper underneath and to the sides as shown in the datasheet, the thermal resistance can get as low as 15 degrees C per watt, or a rise of 75C over ambient. The max operating temp is 150C, so at 50C ambient, it can run at 2.8ADC thru the 3-Phase H-Bridge and dissipate about 5 watts for a junction temperature of 125C, which leaves a 25C safety margin. Now, that's worse case. Most likely, your motor will not use an RMS current of 2.8 A nor will it run all the time at maximum pulse width. With any reduced pulse width and/or reduced motor current, the dissipation in the IC will be less. It will need some extra circuitry to control it, but you should be able to get with just an op-amp for the speed loop (or you could just feed a variable DC voltage properly scaled to control speed), and a current-sense resistor so that the IC protects itself from overcurrent, etc. The datasheet has a complete typical application schematic. If your motor doesn't have hall-effect sensors, then you'll probably need a different IC. There are 3-Ph BDC motor control IC's with built-in power FET's that can control the commutation and speed without hall effect sensors for feedback. Just do a google search and/or use globalspec.com and search for them. Look to IC firms like: IR, Freescale, Allegro, Microchip, etc.

    Good luck,

    Kamran Kazem,
    kkazem
     
  5. jeka616

    Thread Starter Active Member

    Jan 14, 2009
    121
    1
    Thanks for effort and time Kamran.
     
Loading...