SiC MOSFET vs Si IGBT: Turn-Off Current Tail

Device Under Test

Circuit Conditions

Gate resistor R_g 10 Ω

Load current I_load 30 A

Bus voltage V_dc 400 V

Turn-Off Transient

Switching energy E_off– µJ

Peak instantaneous power– kW

Total switching time– ns

Drain/collector voltage v(t)

Channel/tail current i(t)

Instantaneous power p = v·i

How it works

This models a hard-switched inductive-load turn-off (the standard "double-pulse test" used to characterize power devices), with drain/collector current held near I_load by a freewheeling diode while the device blocks the rising bus voltage.

Voltage-rise time:  t_vr = Rg·Qgd / ΔVg
Current-fall time:  t_fi = Rg·Qgs2 / ΔVg
Turn-off energy:     Eoff = ∫ v(t)·i(t) dt

Q_gd (Miller charge) and Q_gs2 are gate-charge parameters the gate driver must supply through R_g at drive swing ΔV_g ≈ 18 V — a larger R_g slows the gate current and stretches both intervals, trading switching speed (and loss) for lower dv/dt and di/dt ringing.

The key material difference: a SiC MOSFET is a majority-carrier device — once the channel pinches off, current stops almost immediately. A Si IGBT is bipolar: during conduction its drift region is flooded with excess minority carriers (conductivity modulation) that cannot be removed by the gate. They must recombine, so the collector current develops a current tail:

I_tail(t) = f_tail·Iload · exp(−t / τ)

with carrier lifetime τ ≈ 100–300 ns. Because the tail current flows while v(t) is already at the full bus voltage V_dc, it dissipates energy roughly proportional to V_dc·I_load·τ — this is the dominant reason SiC power modules switch several times faster than Si IGBTs at the same voltage/current rating, enabling smaller magnetics and higher switching frequencies in EV inverters, solar inverters, and fast chargers.

Device buttons — swap the gate-charge and tail-current parameters between a wide-bandgap SiC MOSFET and a Si IGBT.
R_g — external gate resistance; higher values slow both the voltage-rise and current-fall phases.
I_load / V_dc — the double-pulse test operating point; both scale the dissipated energy roughly linearly.

v(t) i(t) heat / power

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SiC MOSFET vs Si IGBT: Turn-Off Current Tail & Switching Loss