120v variable frequency drive

Discussion in 'The Projects Forum' started by coolguy10786, May 13, 2010.

  1. coolguy10786

    Thread Starter New Member

    Feb 11, 2009
    2
    0
    Hi I'm working on designing a variable frequency drive for a class project. My initial thoughts were to use use 120VAC, rectify by means of a halfwave rectifier, and then invert using mosfets. I've got some IRF610 mosfets that I was going to use to build my h-bridge with. I went with the halfwave rectifier over the fullwave due to issues i saw when trying to bias the mosfets.

    I've been using ltspice for my circuit simulation and it seems to work, but I know that simulation and the actual circuit functionality are not always the same. I plan on using dual element fuses on the incoming ac line rated for 4 amps, and fast acting fuses on the h-bridge. I'm building this run a .02HP motor rated for 1.4 amps.

    I had thought about using a transformer on the input to keep the circuit isolated from main power, but I am unsure if it is necessary since one could just unplug the unit to service it.

    A gate driver for the mosfets would probably be the optimal way to since I wouldn't have the wasted power when keeping the transistors closed. The gate driving transistors are probably necessary; i just had them there for symmetry. The transistors will then be driven by a PWM signal that I'm writing the code for.

    I'm a little new to circuit design so my circuit probably needs a good amount of work. Any advice is greatly appreciated. Thanks!
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,344
    Hello,

    You MUST use a transformer .
    Even if you say the circuit can be unplugged for seervice, a transformer will make it safer.
    Beware voltages over 42 VAC are possible leathal.

    Bertus
     
  3. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Switch to full wave rectification and use MOSFET gate driver ICs to drive the MOSFETs.
     
  4. coolguy10786

    Thread Starter New Member

    Feb 11, 2009
    2
    0
    I had a feeling I should; just wanted to be sure. I've worked with voltages much higher than 120, but safety is always my number one concern. Thank you for the warning.

    Do you have any particular gate driver's in mind? I've seen some that accept the PWM signal, would it better to use one of those?

    Thanks for the replies. I appreciate the help and comments.
     
  5. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    I have used the IR2181 which are suitable for your application too in terms of operating voltage.

    Visit International Rectifier's website to find more.
     
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