A MOSFET and an IGBT can both switch high power, and the choice between them is not about which is “better” but about where the duty sits. The MOSFET wins at moderate voltage and high frequency; the IGBT wins at high voltage and high current where its lower conduction loss and simpler structure take over. The crossover is a voltage, a frequency, and a cost judgment, and the wrong choice wastes money on a capability the design never uses or fails on a loss the other device would not have paid. This article sets the voltage crossover, the conduction curves, the frequency ceiling, the cost comparison, and the selection frame for the 650 V and 1200 V families.
The Voltage Crossover: Why 250 V is the Common Pivot
The MOSFET and IGBT crossover around a few hundred volts, with 250 V a common practical pivot. Below that voltage, a MOSFET’s low on-resistance gives it the better conduction loss at the current a design usually carries, and its fast switching is a bonus. Above it, the IGBT’s lower forward drop at high voltage and current takes over, because the MOSFET’s on-resistance grows with the voltage class while the IGBT’s drop stays relatively flat.
The crossover is a region, not a line, because the exact pivot shifts with current, temperature, and frequency. A design at 300 V and high current may already favor the IGBT; one at 400 V and low current may still prefer the MOSFET. The IGBT guide frames the market and family, and the MOSFET selection guide is the counterpart; this article sets the boundary the two assume.
A worked loss comparison makes the crossover concrete. At 600 V and 20 A, a high-voltage MOSFET with an on-resistance of 80 mOhm dissipates about 32 W of conduction loss, while an IGBT with a 2 V drop dissipates 40 W — the MOSFET wins at this current because the squared term is still modest. Raise the current to 60 A: the MOSFET’s loss jumps to about 290 W, while the IGBT’s stays at 120 W, because its drop is flat. The crossover sits between the two currents, and it is the current, not the voltage alone, that decides which structure wins. A design that names its operating current before choosing the device is already most of the way to the right answer.
The comparison table holds the two loss shapes side by side:
| Device | Loss shape | At high voltage | At high current | Frequency |
|---|---|---|---|---|
| MOSFET | RDS x I2 | Rises with class | Rises with I2 | High |
| IGBT | Drop x I | Stays flat | Rises linearly | Moderate |
The table is the choice in one view: the MOSFET’s loss rises with both voltage class and current squared, while the IGBT’s drop stays flat with class and rises linearly with current. Where the squared term and the frequency stay low enough, the MOSFET wins; where the current is high and the frequency moderate, the IGBT takes over. Reading the table before the spreadsheet is the honest short cut.
Conduction Loss at High Voltage: MOSFET vs IGBT Curves
The conduction-loss difference is the core of the choice, and it follows the device structure. A MOSFET conducts through a resistance, so its loss is the on-resistance times current squared — the resistance grows with the voltage class, so at high voltage the loss climbs. An IGBT conducts through a diode-like junction, so its loss is roughly a fixed drop times current — the drop stays flat with the voltage class, so at high voltage and current the IGBT’s loss is lower.
The curves cross because of the two different shapes. At low current, the MOSFET’s tiny resistance wins; at high current, the IGBT’s flat drop wins because the MOSFET’s squared term runs away. The 1200 V IGBT article and the 650 V IGBT article work the loss curves for their voltage classes, and the MOSFET loss method is the calculator that finds the crossover at the real operating point.
Switching Frequency Ceiling: Why IGBTs Slow Down Above 10 kHz
The switching-frequency ceiling is where the IGBT gives back its conduction advantage. An IGBT carries a tail current at turn-off and a recovery behavior that dissipates energy per switch event, so its switching loss grows with frequency. Above roughly 10 kHz, that switching loss overtakes the conduction saving, and the IGBT stops being competitive against a MOSFET or a SiC device that switches faster.
The ceiling is a real limit, not a marketing claim. A motor drive at 4-16 kHz is the IGBT’s natural zone; a PFC or a server supply at hundreds of kilohertz is not. The 1200 V IGBT motor-drive article sets the frequency context, and the SiC MOSFET article is where the design moves when the frequency pushes past the IGBT’s ceiling.
Cost per Amp and System Simplicity Comparisons
The cost comparison rounds out the choice. An IGBT is often cheaper per amp than a high-voltage MOSFET of the same class, because its simpler structure and higher current density lower the price, and its gate drive is simpler in many applications. A MOSFET’s fast switching may need a more capable driver and a tighter layout, adding system cost even when the part is cheap.
The system-simplicity view matters more than the part price. An IGBT with a simple drive and a robust structure can be the lower total-cost choice in a motor drive, while a MOSFET or SiC device wins where the switching speed justifies the driver and layout expense. The IGBT sourcing guide and the MOSFET selection frame the two sides of the cost ledger.
Picking a Frame for the 650 V and 1200 V Families
The selection frame for the two voltage families follows the crossover. At 650 V, the IGBT suits appliance and induction-heating drives that switch at moderate frequency; the MOSFET or SiC MOSFET suits PFC and server duties that switch fast. At 1200 V, the IGBT dominates the motor-drive and industrial space at 4-16 kHz, and the SiC MOSFET takes over where frequency or efficiency demand it.
The frame is read by the duty, not the chemistry: name the voltage, the frequency, and the current, then the IGBT or the MOSFET falls out. The 650 V IGBT article and the 1200 V IGBT article cover the IGBT side, the SiC MOSFET articles and 1200 V SiC article the MOSFET side, and the IGBT families supply the parts once the frame lands on the IGBT.
A final cost check keeps the frame honest. The IGBT’s lower part price and simpler drive can make it the lower total-cost choice in a motor drive, even when its switching is slower; the MOSFET or SiC device wins on total cost only when the frequency makes the switching-loss and driver savings real. The comparison is therefore not the part price alone but the system ledger — device, driver, heatsink, and the loss the duty pays — and the IGBT sourcing guide and the MOSFET selection guide are the two references that price the whole system. The IGBT-versus-MOSFET choice, closed with the voltage pivot, the conduction curves, the frequency ceiling, and the total-cost ledger, is the decision that every high-power design makes once, and the frame is what makes it right the first time. That is its value in one line. And it is the point of this article.
The IGBT-versus-MOSFET choice, set by the voltage pivot, the conduction curves, the frequency ceiling, and the cost, is the same decision every high-power design makes — and the frame is what keeps it honest.
A worked frequency comparison completes the switching picture. The same 600 V class IGBT that carries a motor drive at 8 kHz comfortably has a per-event switching loss that, at 80 kHz, becomes eight times the energy per second — a switching loss that overwhelms the conduction saving and makes the part run hot. A MOSFET or SiC device at the same 80 kHz keeps the switching term low enough that the frequency is affordable. The 10 kHz ceiling is therefore not a hard number; it is the region where the IGBT’s switching loss overtakes its advantage, and a design that needs the higher frequency must move to the faster family regardless of how attractive the IGBT’s conduction looks cold.
The closing frame for a new design is the four answers the pivot sets. Name the voltage, name the current, name the frequency, and name the cost target; the four numbers fall on the frame and the device follows. A motor drive at 1200 V and 20 A switching at 8 kHz lands on the IGBT. A server PFC at 650 V and 20 A switching at 100 kHz lands on the SiC MOSFET. A low-power 400 V supply at modest frequency may stay with a silicon MOSFET. The IGBT families and the MOSFET families supply the parts, and the SiC families cover the high-frequency extension. The frame, applied with the four numbers, is the whole IGBT-versus-MOSFET method in one decision.