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IRFZ46N MOSFET versus IRLZ34N — Parallax Forums

IRFZ46N MOSFET versus IRLZ34N

Ron CzapalaRon Czapala Posts: 2,418
edited 2010-05-30 17:28 in BASIC Stamp
I have not used MOSFETs before and have been reading various threads pertaining to them.

I want experiment with driving 12volt motors without an H-BRIDGE.

I read that the IRLZ34N was a good "choice for control by logic circuitry"
http://forums.parallax.com/showthread.php?p=759109

I just removed sixtreen IRFZ46N·MOSFETS from an old·Pure Sine Wave APC UPS and was trying to compare datasheets but I am defuddled by all of the specifications.

They are both 55V but the IRZ46N has a "ultra low" RDS(on)·of 16.5m ohm (0.0165 right?) versus 0.035 ohm

Are there any other·significant specs that I should compare?

Also, can you·drive them with PWM signals to control the motor's speed?

Datasheets:
http://datasheet.digchip.com/232/232-12816-0-IRFZ46N.pdf

http://datasheet.digchip.com/232/232-13687-0-IRLZ34N.pdf

Thanks for any help/info!

Post Edited (ronczap) : 5/29/2010 10:40:43 PM GMT

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2010-05-29 23:15
    The IRL series devices are designed to be driven from logic-level circuits (typically +5V). The IRF series devices require a higher gate voltage to switch on completely. They may switch on at +5V, but they won't conduct much current at that gate voltage. There are graphs in the datasheets that show how much current can be carried vs. the gate voltage.

    PWM signals are just rapid on/off pulse sequences. The ratio of on-time to off-time is proportional to the average current conducted. A motor or incandescent lamp provides some inertia so the pulses "smooth out".
  • Ron CzapalaRon Czapala Posts: 2,418
    edited 2010-05-30 00:05
    Thanks Mike! Great explanation.

    I see from the Drain-to-source Current/Gate-to-source voltage charts that the IRLZ34N·does source more current at 5 volts.

    Datasheets have so much info that it's hard to know what to look for - especially if you don't have a strong electronics background...


    Post Edited (Ron Czapala) : 5/30/2010 12:15:12 AM GMT
  • FranklinFranklin Posts: 4,747
    edited 2010-05-30 00:28
    You also need to take into account that if you don't fully turn the device on it is not working at best efficiency and will get hot or fail sooner than one running correctly.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    - Stephen
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2010-05-30 03:44
    For PWMing, the MOSFET's gate capacitance is also a spec that needs consideration. If the gate capacitance and PWM frequency are high, a MOSFET driver will be required for efficient high-speed switching.

    -Phil
  • Ron CzapalaRon Czapala Posts: 2,418
    edited 2010-05-30 11:55
    Phil,

    What do you mean by a MOSFET driver -·another component between the microcontroller and the MOSFET?

    What MOSFET(s) would you recommend to drive directly from a microcontroller·using PWM?·· The IRLZ34N?

    What if you wanted to control the positive line - a P channel, logic level MOSFET?

    Thanks,
    · Ron
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2010-05-30 17:28
    What do you mean by a MOSFET driver - another component between the microcontroller and the MOSFET?

    Yes, something like the TI TPS2814P, for example, or one of Micrel's drivers.

    What MOSFET(s) would you recommend to drive directly from a microcontroller using PWM? The IRLZ34N?

    It depends on the micro's drive capability, its voltage output, and the PWM frequency. The IRLZ34N is fine with a 5V drive, if the PWM rate isn't too high. For a 3.3V drive, the IRF3708 is a better choice.

    What if you wanted to control the positive line - a P channel, logic level MOSFET?

    Yes, but only if the voltage you're sourcing with it is no higher than the "high" output voltage from the micro.

    -Phil
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