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recommend a high voltage digital FET? — Parallax Forums

recommend a high voltage digital FET?

mike56mike56 Posts: 22
edited 2009-06-12 22:17 in Propeller 1
Can someone recommend a digital FET like the FDS6990A used on the servo board but higher voltage (40-50+V)?

Preferably more than 1 mosfet per package.

Also is there a disadvantage to using something like the ULN2003 instead of a N-channel mosfet?·

Also I'd be really nice to have it in PDIP format.

Post Edited (mike56) : 6/10/2009 8:19:32 PM GMT

Comments

  • RaymanRayman Posts: 14,833
    edited 2009-06-11 00:22
    I don't know if it's right for you, but I've used the IRFD210 (n-channel) and IRFD9210 (p-channel) 200V mosfets with some success... They come in 4-pin PDIP. If you look them up in Digikey, you'll see other voltages on the catalog page...

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    My Prop Info&Apps: ·http://www.rayslogic.com/propeller/propeller.htm
  • mike56mike56 Posts: 22
    edited 2009-06-12 08:08
    I looked on digikey and found the Fairchild HUFA76413DK8T :
    http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=HUFA76413DK8TCT-ND

    It says Logic Level Gate, 60V @ 5.1A.

    Can build the same design as the servo board but use the HUFA76413DK8T instead of the FDS6990A ?

    Cost is not significantly different. I don't know too much about mosfets. I want to build a motor driver using the stamp but my supply voltage is 45V so I can't use the servo board.

    From what I can tell, a MOSFET can be used just like a relay right?

    Is there anything I'm missing here?
  • RaymanRayman Posts: 14,833
    edited 2009-06-12 10:30
    Well, it's complicated... In priciple, you can use a mosfet like a relay, provided you give the gate enough voltage, which is sounds like you can do. Also, mosfets usually don't allow that much current... Better check the rating. You may want to use an IGBT instead.

    But, the big problem for you that I forsee is inductive voltage spikes from you motor. These could easily kill your mosfet or igbt... You probably would need to add a free-wheeling diode (like that used inside the ULN chip).

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    My Prop Info&Apps: ·http://www.rayslogic.com/propeller/propeller.htm
  • RaymanRayman Posts: 14,833
    edited 2009-06-12 10:54
    PS: Perhaps the easiest thing to do us use a ULN2803 end to control a real relay that gives power to your motor...

    Check out this thread (not motors, but big contactors):
    http://forums.parallax.com/showthread.php?p=687346

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    Post Edited (Rayman) : 6/12/2009 10:59:50 AM GMT
  • mike56mike56 Posts: 22
    edited 2009-06-12 18:58
    I've heard darlington arrays are pretty slow so I can't PWM them to control the current in a 3 phase motor.

    Any comments about the Fairchild HUFA76413DK8T :
    http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=HUFA76413DK8TCT-ND

    Is it pretty much the same as the FDS6990A but good for 60V?
  • RaymanRayman Posts: 14,833
    edited 2009-06-12 21:04
    I don't know exactly what you're doing and motors are really anything I work with, but it looks good to me assuming that voltage and current are enough for your motor. I think you still need to add a free-wheeling diode though.

    PWM a 3-phase motor? Actually, that sounds a little strange to me...

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    My Prop Info&Apps: ·http://www.rayslogic.com/propeller/propeller.htm
  • mike56mike56 Posts: 22
    edited 2009-06-12 22:17
    By using PWM, one can model the time constant in the inductor and control the current. The same with most motors, when you turn off the power, it takes a while for the current to drop to 0 due to the inductance. By turning it on/off quickly you can set the current inside the motor. Almost the same thing as the time constant in a RC device but a little different. Do the same for all 3 coils.
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