Page 121 - Rashid, Power Electronics Handbook

108 S. Abedinpour and K. Shenai

compared to its maximum continuous current, which is of gate-charge value. This parameter varies as a function of the
described by this parameter. gate-emitter voltage.
Maximum Power Dissipation (P ): This parameter repre- Turn-on Delay Time (t ): This is de®ned as the time
d
D
sents the power dissipation required to raise the junction between 10% of gate voltage to 10% of the ®nal collector

temperature to its maximum value of 150 C, at a case current.

temperature of 25 C. Normally a plot is provided to show Rise Time (t ): This is the time required for the collector
r
the variation of this rating with temperature. current to increase to 90% of its ®nal value from 10% of its
Junction Temperature (T ): Speci®es the allowable range of ®nal value.
j
the IGBT junction temperature during its operation. Turn-off Delay Time (t dðoffÞ ): This is the time between 90%
Clamped Inductive Load Current (I ): This parameter of gate voltage to 10% of ®nal collector voltage.
LM
speci®es the maximum repetitive current that IGBT can turn Fall Time (t ): This is the time required for the collector
f
off under a clamped inductive load. During IGBT turn-on, the current to drop from 90% of its initial value to 10% of its
reverse recovery current of the freewheeling diode in parallel initial value.
with the inductive load increases the IGBT turn-on switching Input Capacitance (C ): The measured gate-emitter capa-
ies
loss. citance when collector is shorted to emitter. The input
Collector-Emitter Leakage Current (I ): This parameter capacitance is the sum of the gate-emitter and the Miller
CES
determines the leakage current at the rated voltage and speci®c capacitance. The gate-emitter capacitance is much larger than
temperature when the gate is shorted to emitter. the Miller capacitance.
Gate-Emitter Threshold Voltage (V GEðthÞ ): This parameter Output Capacitance (C ): The capacitance between collec-
oes
speci®es the gate-emitter voltage range, where the IGBT is tor and emitter when the gate is shorted to the emitter, which
turned on to conduct the collector current. The threshold has the typical pn-junction voltage dependency.
voltage has a negative temperature coef®cient. Threshold Reverse Transfer Capacitance (C ): The Miller capacitance
res
voltage increases linearly with gate-oxide thickness and as between gate and collector, which has a complex voltage
the square root of the p-base doping concentration. Fixed dependency.
surface charge at the oxide-silicon interface and mobile ions in Safe Operating Area (SOA): The safe operating area deter-
the oxide shift the threshold voltage. mines the current and voltage boundary within which the
Collector-Emitter Saturation Voltage (V CEðSATÞ ): This IGBT can be operated without destructive failure. At low
parameter speci®es the collector-emitter forward voltage currents the maximum IGBT voltage is limited by the open-
drop and is a function of collector current, gate voltage, and base transistor breakdown. The parasitic thyristor latch-up
temperature. Reducing the resistance of the MOSFET channel limits the maximum collector current at low voltages. While
and JFET region, and increasing the gain of the pnp-bipolar IGBTs immune to static latch-up may be vulnerable to
transistor can minimize the on-state voltage drop. The voltage dynamic latch-up, operation in short-circuit and inductive
drop across the MOSFET component of IGBT, which provides load switching are conditions that would subject an IGBT to a
the base current of the pnp-transistor is reduced by a larger combined voltage and current stress. A forward-biased safe
channel width, shorter channel length, lower threshold operating area (FBSOA) is de®ned during the turn-on tran-
voltage, and wider gate length. Higher minority carrier life- sient of the inductive load switching when both electron and
time and a thin n-epi region cause high carrier injection and hole current ¯ow in the IGBT in the presence of high voltage
reduce the voltage drop in the drift region. across the device. The reverse-biased safe operating area
Forward Transconductance (g ): Forward transconduc- (RBSOA) is de®ned during the turn-off transient, where
FE
tance is measured with a small variation on the gate voltage, only hole current ¯ows in the IGBT with high voltage across it.
which linearly increases the IGBT collector current to its rated If the time duration of simultaneous high voltage and high

current at 100 C. The transconductance of an IGBT is reduced current is long enough, the IGBT failure will occur because of
at currents much higher than its thermal-handling capability. thermal breakdown. However, if this time duration is short,
Therefore, unlike the bipolar transistors, the current-handling the temperature rise due to power dissipation will not be
capability of IGBTs is limited by thermal consideration and enough to cause thermal breakdown. Under this condition the
not by its gain. At higher temperatures, the transconductance avalanche breakdown occurs at voltage levels lower than the
starts to decrease at lower collector currents. Therefore these breakdown voltage of the device. Compared to the steady-state
features of transconductance protect the IGBT under short- forward blocking condition the much larger charge in the drift
circuit operation. region causes a higher electric ®eld and narrower depletion
ÿ
Total Gate Charge (Q ): This parameter helps to design a region at the p-base and n -drift junction. Under RBSOA
G
suitably sized gate-drive circuit and approximately calculate its conditions there is no electron in the space-charge region and
losses. Because of the minority-carrier behavior of the device, therefore there is a larger increase in electric ®eld than the
the switching times cannot be approximately calculated by use FBSOA condition.