Download 300V PT IGBT Technology

300V IGBTs Displace MOSFETs in Power Supplies
Jonathan Dodge, P.E.
Senior Applications Engineer
Jeff Morrison
Senior Characterization Engineer
Advanced Power Technology
405 S.W. Columbia Street
Bend, OR 97702 USA
Abstract
With recent reductions in both conduction and
switching losses, PT IGBTs now have superior
performance over MOSFETs rated from 200 to
300 Volts. This paper compares the overall
performance of these 300 Volt IGBTs with 300
Volt power MOSFETs. On-state voltage is
greatly reduced due to conductivity modulation
in the IGBT, yet total switching losses are almost
identical to that of MOSFETs. Due to active
minority carrier lifetime control, these PT IGBTs
are suitable for high frequency power supply
applications. Tests in a hard-switched circuit
show that the 300 Volt IGBTs provide a lower
cost, higher performance alternative to power
MOSFETs.
lowest on resistance has the lowest conduction
loss.
For power MOSFETs with blocking voltage
above about 200V, the majority of on resistance
is in the drift region rather than the channel.
IGBTs address the on resistance issue at its
core by significantly reducing the drift region
resistance. This is done by injecting minority
carriers into the drift region (conductivity
modulation and bipolar current flow) [1].
Introduction
IGBTs are replacing MOSFETs in many high
frequency SMPS designs [1]. The use of 300V
IGBTs in power supplies is a relatively new
development.
Recent advancements in PT
IGBT technology such as Power MOS 7 IGBTs
make it possible for 300V IGBTs to replace
power MOSFETs, even with the lower RDS(on) at
200V to 300V ratings. The main advantage of
these new 300V IGBTs is lower cost while
maintaining performance similar to power
MOSFETs. Alternatively, efficiency and power
density can be significantly improved at the
same cost.
300V PT IGBT Technology
IGBTs can be thought of as having on
resistance similar to MOSFETs.
The
relationship at any given voltage and current is
simply Ohm’s law: on-state voltage equals
current times on resistance. IGBT on resistance
is it on-state voltage (VCE(on)) divided by collector
current IC, just like MOSFET RDS(on) is drainsource on-state voltage divided by drain current
ID. Care must be taken to use the voltage
corresponding to the operating temperature.
Conduction loss is the product of on resistance
squared and current, so the device with the
Figure 1 On-State Voltage and Resistance
Comparison: 300V Power MOSFET vs. 300V
PT IGBT @ 125 C, 15V Gate Bias
Figure 1 shows the on-state voltage versus
current of APT30M75BLL, a 44A, 300V power
MOSFET and APT83GU30B, a 300V, 83A PT
IGBT, each at 125 C. On resistance at 22A is
shown for each. At current above about 7
Amps, the 300V IGBT has significantly lower on
resistance than the 300V MOSFET.
This
dramatic improvement in on resistance enables:
 smaller IGBT chip area for the same power
converted as the MOSFET – lower cost
 higher efficiency for similar chip area as the
MOSFET
 higher power density
As with higher voltage IGBTs, the tradeoff of
lower on resistance by conductivity modulation
is a tail current at turn-off due to the minority
carriers. This tail current increases the turn-off
switching loss Eoff. Conductivity modulation
does not negatively impact IGBT turn-on energy
Eon but rather reduces it. Total switching losses
remain about the same as a 200V to 300V
power MOSFET of similar current rating.
Note that power MOSFET current ratings are
made with a case temperature of 25 C. It is the
IGBT IC2 rating, with the case at elevated
temperature, which should be compared with the
MOSFET current rating. The difference in case
temperatures in the current ratings is accounted
for by the greatly reduced conduction loss of the
IGBT.
Minority carrier lifetime control significantly
reduces the tail current and the consequent Eoff
penalty. Electron irradiation is generally used in
PT IGBTs as the method of controlling minority
carrier lifetime.
Lifetime control has three
tradeoffs:
1. Eoff versus VCE(on), or on resistance
2. Wider distribution VCE(on)
3. Increased leakage current at high
temperature, which is the reason PT
IGBTs are not rated above 150 C.
More aggressive lifetime control decreases Eoff
but increases VCE(on) at a given current. For any
given IGBT design, the Eoff versus VCE(on)
operating point can be targeted along a curve of
Eoff versus VCE(on). This curve is defined by the
technology used in the design of the IGBT. An
improvement in technology results in lower Eoff
and VCE(on) both. It is a recent improvement in
technology that enables 300V Power MOS 7 
IGBTs to replace 200 to 300V MOSFETs in
power supplies.
Previously IGBTs mostly
replaced MOSFETs with a blocking voltage of
400V and higher because of the lower drift
region resistance of lower voltage MOSFETs
combined with the MOSFET’s unrivalled
switching speed.
When comparing power supply IGBTs with
MOSFETs, it may seem that the IGBT on-state
voltage is high as stated in a datasheet because
it directly correlates to conduction loss.
However, if RDS(on) of a similarly rated MOSFET
is used to calculate on-state voltage, it becomes
clear that the conduction loss of the IGBT is in
fact significantly lower. This is because the
MOSFET RDS(on) increases quickly with higher
currents (See Figure 1) and with normal
operating temperature (See Figure 2). In a
power supply, a lower VCE(on) (longer minority
carrier lifetime) would result in unacceptably
high switching losses with conduction loss being
a tiny portion of the total IGBT losses. The end
result with the IGBT is lower conduction loss and
total switching losses similar to a MOSFET with
larger chip area, as will be shown.
The wider distribution in VCE(on) is the main
cause of difficulty in paralleling PT IGBTs. The
temperature coefficient is actually a secondary
consideration for paralleling. Fortunately for
300V IGBTs, relatively little lifetime control is
needed because the drift region is less resistive
compared to higher voltage PT IGBTs, so fewer
minority carriers are injected into the drift region
during conduction. The lower level of lifetime
control results in a narrower distribution of VCE(on)
compared to higher voltage IGBTs, and hence
easier paralleling.
Punch-through technology is likely to remain the
technology of choice for 300V IGBTs because of
the difficulty in manufacturing a non punchthrough technology IGBT with wafers thin
enough for competitive performance with less
than about a 600V rating.
A final distinguishing feature of 300V PT IGBTs
is the temperature coefficient of on resistance
(analogous to the temperature coefficient of
VCE(on)).
Figure 2 On Resistance vs. Temperature for a
300V Power MOSFET and 300V PT IGBT,
Each at 22A, 15V Gate Bias
The slopes of the curves in figure 2 indicate the
temperature coefficient of on resistance for an
APT30M75BLL MOSFET and an APT83GU30B
IGBT.
The IGBT has a slightly negative
temperature coefficient at 22 Amps, and a
slightly positive temperature coefficient above
about 44 Amps. The flat temperature coefficient
is beneficial for current overload capability. The
positive temperature coefficient at higher current
makes paralleling easier. The 300V power
MOSFET temperature coefficient is always
positive and very strong as shown in Figure 1.
This is a typical power MOSFET characteristic.
Performance Comparison
Tests done in a hard-switched inductive circuit
reveal the distribution of losses as well as total
losses in a 300V Power MOS 7 IGBT and
MOSFET.
Power Lo ss (Watts)
100
80
Psw(off)
60
Psw(on)
40
Pcond
Figure 4 Capacitance Comparison: 300V
MOSFET vs. Smaller Size 300V PT IGBT
20
0
IGBT
MOSFET
APT 32GU30B
APT 30M75BLL
Figure 3 Total Losses for a 300V MOSFET &
300V IGBT @ 200V, 22A, 150kHz, 50% Duty,
Hard Switched, RG = 20 and TJ = 125 C
Each
Figure 3 shows total losses for APT30M75BLL
and APT83GU30B operating at 200V, 22A
switched current, and 150kHz hard switching.
Psw(off) is turn-off switching power loss (Eoff
times switching frequency), Psw(on) is turn-on
switching power loss, and Pcond is the
conduction loss. In spite of the higher turn-off
switching loss, the IGBT has lowest total losses
because of lower conduction and turn-on
switching losses. Total switching losses are
almost the same for the IGBT and the MOSFET,
so changing the switching frequency would still
result in lower total losses in the IGBT. Clearly
the IGBT is a suitable replacement for the
MOSFET in this case. Conduction loss in each
case is a significant portion of total losses, so
choosing a larger device or paralleling devices
would result in a noticeable reduction in total
power loss.
In Figure 3, it is important to remember that the
chip area of the IGBT is much smaller than that
of the MOSFET. So a lower cost 300V IGBT
can replace a 200V to 300V MOSFET at
reduced cost, higher power density, and
possibly higher efficiency. Alternatively, a 300V
IGBT of similar chip area as a MOSFET can
result in significantly higher efficiency.
The gate drive requirements are very similar to a
MOSFET, but lower power gate driver can be
used because of the smaller chip area and
capacitance of the IGBT for the same power
level as a MOSFET, as shown in Figure 4.
Because of the lower capacitance, a higher gate
resistance value may be required to maintain
similar di/dt and dv/dt at turn-on compared to a
200V to 300V MOSFET. Negative gate drive is
completely optional and not necessary.
Although a 10V gate drive supply voltage can be
used, 12 to 15 Volts is recommended for these
300V IGBTs.
Soft Switching
The turn-on of an IGBT is very similar to a power
MOSFET, so these 300V IGBTs are certainly
suitable for soft turn-on (either zero voltage or
zero current). Zero current turn-off also yields
good results with both IGBTs and power
MOSFETs. IGBTs tend to perform poorly with
zero voltage turn-off soft switching because the
IGBT relies on collector-emitter voltage to sweep
out minority carriers. This effect is compensated
for somewhat by active minority carrier lifetime
control in the Power MOS 7 IGBT design.
Lifetime control results in a shorter tail current,
even with no collector-emitter voltage applied.
However, the absence of collector-emitter
voltage at turn-off deprives the IGBT of sweepout of minority carriers, so the zero-voltage turnoff speed cannot match that of a power
MOSFET.
[1] J. Dodge, T. Loder; “Latest Technology PT
IGBTs vs. Power MOSFETs”, PCIM China
2003, Advanced Power Technology