TO247-3 or TO247-4 PIN MOSFET/IGBT ?
most of the time we are stuck with on semiconductor component selection and at the end when we are done with specifications criteria, the last selection criteria left is what should be the pin of the mosfet or IGBT that we should choose, it should be 3 pin or 4pin and how do we decide this difference. and what is the impact of number of pins on the design. in this blog we will find out how much number of pin should be go with along with the cost factor.
TO247-3 AND TO247-4 PIN MOSFET/IGBT
for our study we will choose Infineon IGBTs with part number IKZA75N65EH7 and IKW75N65EH5 both are 650V and 75A IGBT.
lets try to understand what’s makes the difference between TO247-3 and TO247-4 pin IGBT or Mosfet. consider the below image from infineon app note reference.
in 3 pin Mosfet the gate drive circuit is connected with source so the reference grounds for both gate and power path is same, due to which when there is high switching current transition happens a voltage is developed across the parasitic inductance of the source. due to this voltage the gate to source voltage VGS sees a voltage drop and drain to source resistance is slightly increased.
whereas in 4pin Mosfet or IGBT there is a separate pin for the gate drive circuit called kelvin connection and the reference ground in this case is separate for both gate and power path due to which gate to source voltage VGS remains unchanged at the mosfet pin terminals which is similar to the drive output. thus mosfet gate voltage remains tuned and there is no shift in the characteristics.
consider the datasheet of IKZA75N65EH7 the total switching loss in this 4 pin IGBT is 1.6mjoule.
whereas consider the datasheet of IKW75N65EH5 the total switching loss in this 3 pin IGBT is 3.2mjoule
other than this these losses also varies widely wrt switching current, temperature, voltage VCE see characteristics for more details.
it is clearly evident that 4 pin mosfet has significant lower switching losses as compared to 3 pin mosfet or igbt. the cost of these mosfet greatly depends on the year of production, availability, quantity, technology of the die used in it. refer to the below video for more interactive understanding.