Form " C " Switch using PWR MOSFET help

Discussion in 'General Electronics Chat' started by hct203, Dec 25, 2013.

  1. hct203

    Thread Starter New Member

    Mar 18, 2012
    Seeking help with designing a form " C " circuit using power FET.

    Looking to us IRF1324S-7PPBF it is a 24V 0.00165 Rdon , using 8 to create the Form C relay , (2 set in parallel with 4 FET connect source to source gate to gate with all the Drain leads acting as the NO .COMMON . NC connection

    Catch is need to use completely isolated gate drive to the two set , been looking at using Photovoltaic coupler such as TLP3904 /TLP3914/TLP3924 or TLP590B made by Toshiba , IR make a similar units to high price .

    The probleme I need resolved is how to drive the big gate to source capacitance on those FET using the Photocoupler .

    This is a real project that I have a order for to produce large quantity of Solid State relay Form " C" in the 100 to 300 AMPs region ( will be paralleling FET making situation worst ) working voltage is less than 2.0Volt switching .
    Need to go from on to off and on in low microsecond or better .

    Who ever is able to able should contact me there is money for a successful design, and good possibility of long term income from future sale.

    Can be reached either by phone <SNIP> or on this site , I am presently in San Antonio TX
    Last edited by a moderator: Dec 26, 2013
  2. ronv

    AAC Fanatic!

    Nov 12, 2008
    I could be wrong (I often am) but I don't think you can get there with 2 enhancement mode mosfets.
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    You'd have to design for Vgs(th) =4V max (as per spec). How will you switch the FETs fully on (i.e. Vgs ~ 10V) if your "working voltage is less than 2.0Volt switching ."?
    Total gate charge is specified as (typically) 122nC, so four FETs in parallel would be 488nC. To charge the total gate capacitance in 1uS would require 488mA.