I measured the input capacitance of a MOSFET and found it was greater than an IGBT. Why is this? Is it due to the Miller capacitance seen in a MOSFET?

  • 1
    \$\begingroup\$ who says it is greater? \$\endgroup\$ – JonRB Apr 30 '17 at 21:07
  • \$\begingroup\$ Edited my original post! I assume it's therefore not supposed to be? \$\endgroup\$ – user3447255 Apr 30 '17 at 22:39
  • \$\begingroup\$ are you comparing a 1000A MOSFET to a 10A IGBT? What exactly are you doing? \$\endgroup\$ – JonRB Apr 30 '17 at 23:24
  • \$\begingroup\$ I am measuring the input capacitance on 2 transistors - a SiC Power MOSFET and IGBT - on a double pulse circuit which has a 470uH inductor and Vdc of 60V. The MOSFET is rated 1.2kV 36A whilst the IGBT is rated 1.2kV 26A. \$\endgroup\$ – user3447255 May 1 '17 at 11:58

Miller capacitance is nothing that you can easily measure with a cap-meter. The effect comes from the voltage on one pin falling such that less voltage difference is seen on more of the area, such that more charge can flow on the gate. For an IGBT this effect is not present so much, since the MOSFET in front of the BJT does not see the full voltage swing which a single mosfet would see if it was used instead. Further, since there is more amplification going on in an IGBT, it probably has a much smaller MOSFET inside while the BJT is big.

So it is to be expected that in an IGBT and a MOSFET with roughly the same capabilities, the IGBT has smaller capacity.


Miller Effect works like this:


simulate this circuit – Schematic created using CircuitLab


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.