I want to use a MOSFET to switch 400V to a circuit. I can switch low-side using an n-channel MOSFET, but it's more convenient to have the circuit with its ground fixed. So I want to switch high-side, but I don't see how I can use a low voltage for the switching (0 – 5V).
I am switching with a 0/5V square pulse and I need Vsg > |Vt| for the switch to be on (i.e. my load is to be connected to Vdd = 400V). With the configuration below, the MOSFET will be on regardless of if I have a HIGH or a LOW on my input pulse.
Does this mean my switching pulse needs to be 0/400V square pulse (a 400V on gate would give Vsg = 0V < |Vt|, turning the FET off)?
My MOSFET: 500V infeneon IPW50R190CE
Switching frequencies: 10 MHz
Best Answer
Mosfet Vgs max is typically +-20V (check the spec-sheet of your chosen device) so you need some intermediate circuit so you only pull the gate below your rail by less than 20V
For low frequency switching applications, something like this is typical.
simulate this circuit – Schematic created using CircuitLab
Set the values of R1 and R2 to voltage divide your supply to set the right Vgs voltage on M1 when Q1 is on. Set R3 so there is enough current in that divider when your logic level is high.
For high voltages you will be using fairly high values for R1 and R2 to keep the current and power levels reasonable. That means the switch will not be very fast. If you want this for a PWM application you will need a more active driver.