I have a DC motor that needs and works nearly 400v and 20A. I chose FDL100N50 for n-channel mosfet also IXTK40P50P for p-channel mosfet. I connect a 4n35 optocupler for output of every mosfet. Are those suitable for this h bridge?

I couldn't find same caracteristics mosfet for n and p channel.

  • FDL100N50: 500v, 100 A, 2.5 KW , n-channel
  • IXTK40P50P: 500V, 40A, 890W , p-channel

enter image description here

  • 2
    \$\begingroup\$ Welcome to EE.SE. You should hyperlink (neatly) to the datasheets for the devices mentioned. You probably also need a more complete schematic to be sure everyone understands your idea. You can add one in using the CircuitLab button on the editor toolbar. Double-click a component to edit its properties. 'R' = rotate, 'H' = horizontal flip. 'V' = vertical flip. When you use the CircuitLab button an editable schematic is saved in your post. That makes it easy for us to copy and edit in our answers. You don't need a CircuitLab account, no screengrabs, no image uploads, no background grid. \$\endgroup\$
    – Transistor
    Mar 23, 2019 at 8:33
  • \$\begingroup\$ If you are planning PWM what is the DCR of the motor 2Ω ? and all the other parameters like inertia? RPM? Then how will you limit Pd or temp rise on start/stop? Normally you need huge heatsinks unless FET is rated for 10x motor current or you accelerate very slowly. \$\endgroup\$ Mar 23, 2019 at 8:54
  • \$\begingroup\$ Get your RDs on and then calculate the power dissipation and then rethink \$\endgroup\$
    – Autistic
    Mar 23, 2019 at 9:15
  • \$\begingroup\$ Do you think that mosfets i chose are suitable? \$\endgroup\$
    – user216229
    Mar 23, 2019 at 9:40
  • \$\begingroup\$ When someone says , a motor "runs at" without "surge current" and inertia, it always means they know nothing about motor current and have not read any answers I have made on this site for RdsOn and motors. I doubt any MOSFET will work here . It needs an IGBT or equiv. or a better system design. Start with physics 101 on Energy, Power \$\endgroup\$ Mar 23, 2019 at 15:26

1 Answer 1


You cannot solve this problem of driving a 400V 20A motor using Pch MOSFETs. They do not exist with sufficient 600V Vds and $$Pd= (R_{dsOn}+DCR_{motor}) * I_{sc}²$$ (Isc=start current = start surge) for motor winding DC resistance, DCR causing worst-case surge current \$I_{sc}=V_{dc}/(DCR+R_{on})\$ (Ron of bridge = Rdson (Pch+Nch)).

Here your Pch is 350 mOHms and DC motors draw 8 to 12x rated current on startup. This means 400V/20A=20hms so while rated motor is 400*20A=8kW , surge power is 8 to 12x this if full acceleration or an average power draw of 80kW.

So you are planning to use a 5mA Optoisolator to drive a 80kW surge load. That will not work. Then the typ. full acceleration surge current is 200A²*RdsOn= 14kW means the mechanical guy or "you" have to design a heatsink for that surge power dissipation in the Pch for some period of time.

Now your Tesla race car driver is really in the hot-seat.

It MUST be a Quad Nch FET or IGBT full-bridge using the lower side for PWM to create a boost voltage to drive the high side Nch switches.

  • \$\begingroup\$ Whould you mind desining a schema for me, please? \$\endgroup\$
    – user216229
    Mar 25, 2019 at 18:30
  • \$\begingroup\$ You need to do more research. It is far too much time for someone to pick parts and design a schematic for you. Even if they did, you would still blow something up because there's more to it than just a schematic. Do more reading in the direction pointed out by others. \$\endgroup\$
    – DKNguyen
    Mar 25, 2019 at 19:33
  • \$\begingroup\$ RPM is most important problem for me \$\endgroup\$
    – user216229
    Mar 26, 2019 at 18:42
  • \$\begingroup\$ You can easily find full bridge designs on the web with IGBT or quad Nfet. If you do not understand what is T=L/R then you are over your head, \$\endgroup\$ Mar 26, 2019 at 20:08

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