choosing DC H-bridge Mosfets with PWM input

Discussion in 'General Electronics Chat' started by bassplayer142, May 4, 2010.

  1. bassplayer142

    Thread Starter Active Member

    Jan 2, 2007
    89
    0
    I am using a pwm input from a micro to control a motor. I looked into the lmd18200 from another post here but the price tag is steep and making one would be fun. So what is a good cmos controlled mosfet that I can use to control the motor. I would like one that would be capable of up to 12V and maybe 3-5 amps. I figure with external mosfets that shouldn't be an issue. I just want the mosfets to be cheap and easily switchable with a micro. A circuit schematic would work also as long as it shows the parts. Thanks!
     
  2. miniElectronics

    Member

    Aug 4, 2009
    20
    0
    Try motor driver L298. it costs about 3$.
     
  3. kkazem

    Active Member

    Jul 23, 2009
    160
    26
    Hi,
    You'll have to be very careful about this. Unless you're PWM carrier frequency is quite low, like a few hundred hertz, you cannot drive the power MOSFETs with standard CMOS logic, as they are not suited for it. The power MOSFETs, although not needing any steady-state current as they are electrically isolated from the Drain and Source, they do have significant capacitance that in a 20KHz PWM usually requires a minimum of 1amp to 2amps during the transitions. You either need to design your own MOSFET driver or use one of many off-the-shelf units. Another factor is that to drive the upper fet in a Half or Full MOSFET bridge, you need 12 to 15V above it's source, which is floating. This is usually done with an ultrafast diode and a 0.1uF to 1uF ceramic cap. These mosfet drivers are not incredibly expensive and I can recommend for ease of use and very good operating characteristics up to about 50KHZ carrier frequency, the International Rectifier IR2110 half-bridge driver IC. You'll need 2 each of them for a full H-bridge.

    The layout is very critical between the driver IC and the MOSFETs and I recommend as a necessity, that you thoroughly read the application notes from IR on the IR2110 IC, whether you use it or not. The principle's stated in there app notes apply to any high-speed MOSFET driver.

    Regards,
    Kamran Kazem
     
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