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p30-32 Feature Semikron 3/16/06 14:10 Page 30
30 IGBT DRIVERS www.semikron.com
Plug and Play IGBT Driver Cores
for Converters
The key component of every power electronic system is – besides the power modules themselves – the
IGBT driver which forms the vital interface between the power transistor and the controller. For this reason,
the choice of driver is closely linked with the degree of reliability of a converter solution. At the same time,
the driver should guarantee maximum system flexibility and user-friendliness. Markus Hermwille,
Product Manager Electronics, SEMIKRON Elektronik, Nuremberg, Germany
FRANCAIS
Outre les modules de puissance, le composant clé de tout
système électronique de puissance est l’entraînement à transistor
de puissance à porte isolée qui constitue l’interface essentielle
entre le transistor de puissance et le contrôleur. Pour cette raison,
le choix d’un entraînement est étroitement lié au degré de fiabilité
de la solution de convertisseur. Simultanément, l’entraînement doit
garantir une flexibilité système et une convivialité maximales.
Markus Hermwille, Product Manager Electronics,
SEMIKRON Elektronik, Nuremberg, Allemagne
DEUTSCH
Die Schlüsselkomponente jedes leistungselektronischen Systems
ist – neben den Leistungsmodulen selber – der IGBT-Treiber als
vitale Schnittstelle zwischen dem Leistungstransistor und dem
Controller. Aus diesem Grund ist die Auswahl des Treibers eng
verbunden mit dem Grad der Zuverlässigkeit einer
Umrichterlösung. Gleichzeitig sollte der Treiber eine maximale
Systemflexibilität und Anwenderfreundlichkeit garantieren.
Markus Hermwille, Product Manager Electronics,
SEMIKRON Elektronik, Nürnberg, Deutschland
In a power electronics converter a
microcontroller, for example, provides the
digital control signals needed to control
the overall behaviour. The function of the
IGBT driver (Figure 1) is to convert the
incoming digital signals into signals with
sufficient power to ensure safe switching
of the IGBTs. On the other hand, the
IGBT driver has to provide electrical
isolation between the voltage potentials of
the microcontroller and the power
transistors. The use of protection elements
is also recommended in order to ensure
that power modules are properly and
efficiently protected in the event of system
faults.
Thus, drivers used in IGBT power
modules have to fulfil both gate-drive and
protection functions. They must also
provide potential isolation between the
control system and the power
semiconductor and be suitable for use in
many different IGBT configurations. To fully
meet these demands, optimised gate-drive
electronics is required. This means finding
the optimum balance between factors such
as functionality, flexibility and costefficiency,
a balance which has been
achieved in the new driver core concept
SKYPER.
Figure 2 shows the block diagram of the
driver core. This driver core is a half-bridge
driver comprising all the basic driver
functions, potential isolation, protection
functions such as V CE monitoring, short
pulse suppression, under-voltage
monitoring and dead time. By using
Application Specific Integrated Circuits
(ASICs) and a driver concept based on
fundamental driver functions, fewer
components than in conventional driver
solutions are needed. The driver cores
functions with a 15V regulated power
supply and process 15V digital control
signals.
Figure 1: Half-bridge IGBT driver comprising all
basic driver functions
Electrical isolation
The most important requirements for
potential isolation are high isolation voltage
and sufficient dv/dt ruggedness. High dv/dt
ruggedness can be achieved using small
coupling capacitances within the pF range
from the primary to the secondary side.
This will minimise signal transmission
interference caused by displacement
currents during switching. In the case of
inverters, the fast switching of the IGBTs
causes steep voltage steps (high dv/dt
values). It is therefore important to take
into account that noise signals may affect
the control signals. These noise signals can
reach the control system via capacitive
coupling of the device used for electrical
isolation.
In the driver core shown, the power
switches (secondary side) are isolated from
the signal processing component (primary
side) by magnetic transformers which
transfer the driver signals, driving energy
and error signals. This means that the
driver core is suitable for IGBTs up to
1700V.
Potential isolation using signal
transformers (pulse transformers) provides
high isolation and has the added advantage
of high dv/dt ruggedness (50kV/µs)
between the primary and the secondary
side. Unlike solutions with opto couplers,
signal transformers are less susceptible to
faults and also allow bi-directional signal
transfer.
An isolated ferrite transformer is used to
supply the secondary side of the driver and
provide the power needed to switch the
IGBTs. Figure 3 shows the circuitry of the
DC/DC converter. The components used
for signal generation are integrated into an
Application Specific Integrated Circuit
(ASIC). Via the complementary 500kHz
clock outputs TRP and TRN a p-channel
and n-channel MOSFET are driven. To
prevent short circuits occurring in the
bridge-arms of the complementary
MOSFETs the 15V signals are interlocked.
Issue 2 2006
Power Electronics Europe

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www.semikron.com IGBT DRIVERS 31
Figure 2: Block
diagram of SKYPER
On the secondary side, rectification and
voltage stabilization is carried out in order
to generate a positive and a negative
voltage. Due to the integrated DC/DC
converter, an external, isolated supply
voltage is not needed.
Output stage
The switching behaviour of IGBTs can be
controlled by recharging the gate
capacitance. In the driver cores, gate
capacitance recharging is controlled with
resistors. Figure 4 shows an example of an
output stage. The output buffer of the
driver cores is supplied by the +15V/-7V
from the DC/DC converter. If the operation
proceeds normally (no fault), the signal is
transmitted to the gate of the IGBT through
the gate resistor R G . The gate resistor in
Figure 4 has been divided up into two
resistors R Gon and R Goff for turn-on and
turn-off respectively. The main advantage is
that this configuration offers the possibility
of separate optimisation of turn-on and
turn-off with regard to turn-on overc-urrent
and turn-off over-voltage and to short-circuit
behaviour.
The gate-emitter resistor (R GE ) prevents
unintentional charging of the gate
capacitance under driver operating
conditions with highly resistive output levels
(switching, off-state and driver supply
voltage breakdown). Every output stage
recharges the gates with up to 15A of peak
current. The high pulse output currents
allow for short turn-on and turn-off times
for the IGBTs, as the IGBT gate
capacitances are recharged quickly,
meaning that IGBT modules with higher
currents can be switched or IGBTs
connected in parallel.
The charge needed to switch the IGBTs
essentially depends on the type of IGBT
technology used, the chip size, the DC
link voltage and the gate voltage. The
output stages of the driver cores can
provide an output charge per pulse of
up to 6.3µC. With a view to the mean
output current value of 50mA and the
IGBTs used, switching frequencies of up to
50kHz can be achieved. This is enough to
drive 1400A/1200V half-bridge IGBT
modules.
Protection electronics
On the secondary side, to protect the
IGBTs from over-load situations such as
short circuits, each output stage has an
integrated dynamic monitoring function for
the saturation voltage. This monitoring
function compares the collector-emitter
voltage of the IGBT with an external
adjustable reference value (V CEstat ) after
the given blanking time (t bl ), which can be
set using external circuitry. If the reference
value is exceeded, the given stage will be
turned off. The short circuit is sent to the
error memory on the primary side of the
driver core in the form of an error signal,
where it is recorded and all outputs
subsequently turned off. To prevent the
turn-on on a short-circuit, the signal path for
subsequent turn-on signals remains
blocked until resetting is carried out via a
reset pulse. In IGBT desaturation
monitoring, dynamic saturation voltage
characteristics must also be taken into
consideration. In the first microseconds of
turn-on the collector-emitter voltage is far
higher than the final value V CEsat . The
Figure 3: Primary
circuit of the DC/DC
converter
Figure 4: MOSFET
output stage
Power Electronics Europe Issue 2 2006

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IGBT DRIVERS
www.semikron.com
Figure 5: Dynamic saturation voltage
characteristic
response characteristics of the monitoring
circuit therefore have to correspond with
the V CEsat profile during the blanking time
(Figure 5).
If the driver supply voltage drops
substantially, the gate-drive and protection
and functions may fail. Moreover, the
power transistors can no longer be fully
controlled or blocked and the IGBT will
operate in the linear area due to too low a
gate voltage. If the IGBT operates in the
linear area, there will be higher losses and
thermal overloading of the IGBT may occur.
To ensure that dropping of the driver supply
voltage is detected, the supply voltage is
monitored and, in the event of an error, the
integrated error memory set. As is the case
with the detection of a short circuit, the
error memory blocks the input pulse for
both output stages and sets the error
output of the driver core.
To avoid a bridge arm short circuit, IGBTs
of the same bridge arm must not be
switched on at the same time in voltage
source circuits. Due to the dead time
generation in the driver core both output
stages are interlocked even in case of
errors in the input signals.
On the basis of the driver core described
above (standard version), a premium
version has also been developed which
incorporates additional functions such as
error input on the secondary side and
extended error management functions. A
soft turn-off has also been added to
improve short circuit protection. In case of
short circuit, this function turns off the
IGBT at a lower speed and hence
reduces the DC voltage overshoot, enabling
the use of higher DC-bus voltages. This
means an increase in the final output
power.
Solder or plug connection
The driver cores are suitable for direct
PCB assembly by solder or plug
connection and can be adapted to many
different IGBT modules. In this way,
solutions can be developed which boast
the functions common in standard
intelligent power modules plus the
flexibility of conventional modules thanks to
the possible optimisation of switching
characteristics. The flexible assembly
allows for the possibility to directly
assemble the driver core on top of the
IGBT module. As a result a short
connection between driver core and IGBT
module can be reached.
The driver cores offer the designer
simple gate-driver electronics with
potential isolation and protection
electronics, completely qualified and
100% tested. The developer is saving cost
and time for the development and
qualification and can therefore focus on the
major task at hand, the design of the
inverter. Challenges such as time-to-market
by reducing development time can be
solved by using ready to use driver cores.
Since an individual configuration of the
driver core is still possible, the driver
cores can be integrated in different
application topologies. The same driver
core can be used in topologies for
AC/DC drives, UPS, power supply and
welding.