7 Driver Electronic – PCB Drivers 30-09-2008 © by SEMIKRON
Error monitoring and error memory
The error memory is set in case of under-voltage or
short-circuit of the IGBTs. In case of short-circuit, an error
signal is transmitted by the VCE-input via the pulse
transformers to the error memory. The error memory will
lock all switching pulses to the IGBTs and trigger the error
output (P10) of the driver. The error output consists of an
open collector transistor, which directs the signal to earth
in case of error. SEMIKRON recommends the user to
provide for a pull-up resistor directly connected to the error
evaluation board and to adapt the error level to the desired
signal voltage this way. The open collector transistor may
be connected to max. 30 V / 15 mA. If several SKHI 22Bs
are used in one device, the error terminals may also be
paralleled.
ATTENTION: Only the SKHI 22A / 21A is equipped with
an internal pull-up resistor of 10 kΩ versus VS. The
SKHI 22B does not contain an internal pull-up resistor.
The error memory may only be reset, if no error is pending
and both cycle signal inputs are set to low for > 9 μs at the
same time.
Pulse transformer set
The transformer set consists of two pulse transformers
one is used bidirectional for turn-on and turn-off signals of
the IGBT and the error feedback between primary and
secondary side, the other one for the DC/DC-converter.
The DC/DC-converter serves as potential-separation and
power supply for the two secondary sides of the driver.
The isolation voltage for the "H4"-type is 4000 VAC and
2500 VAC for all other types.
The secondary side consists of two symmetrical
driver switches integrating the following components:
Supply voltage
The voltage supply consists of a rectifier, a capacitor, a
voltage controller for - 7 V and + 15 V and a + 10 V
reference voltage.
Gate driver
The output transistors of the power drivers are MOSFETs.
The sources of the MOSFETs are separately connected to
external terminals in order to provide setting of the turn-on
and turn-off speed by the external resistors RON and ROFF.
Do not connect the terminals S7 with S8 and S13 with
S14, respectively. The IGBT is turned on by the driver at +
15 V by RON and turned off at - 7 V by ROFF. RON and ROFF
may not chosen below 3 Ω. In order to ensure locking of
the IGBT even when the driver supply voltage is turned off,
a 22 kΩ-resistor versus the emitter output (E) has been
integrated at output GOFF.
VCE-monitoring
The VCE-monitoring controls the collector-emitter voltage
VCE of the IGBT during its on-state. VCE is internally limited
to 10 V. If the reference voltage VCEref is exceeded, the
IGBT will be switched off and an error is indicated. The
reference voltage VCEref may dynamically be adapted to
the IGBTs switching behaviour. Immediately after turn-on
of the IGBT, a higher value is effective than in the steady
state. This value will, however, be reset, when the
IGBT is turned off. VCEstat is the steady-state value of VCEref
and is adjusted to the required maximum value for each
IGBT by an external resistor RCE to be connected between
the terminals CCE (S6/S15) and E (S9/S12). It may not
exceed 10 V. The time constant for the delay of VCEref may
be increased by an external capacitor CCE, which is
connected in parallel to RCE. It controls the time tmin which
passes after turn-on of the IGBT before the
VCE-monitoring is activated. This makes possible any
adaptation to the switching behavior of any of the IGBTs.
After tmin has passed, the VCE-monitoring will be triggered
as soon as VCE > VCEref and will turn off the IGBT.
External components and possible adjust-
ments of the hybrid driver
Fig. 1 shows the required external components for
adjustment and adaptation to the power module.
VCE - monitoring adjustment
The external components RCE and CCE are applied for
adjusting the steady-state threshold and the short-circuit
monitoring dynamic. RCE and CCE are connected in
parallel to the terminals CCE (S15/ S6) and E (S12/ S9) .
Fig. 4 VCEstat in dependence of RCE (Tamb = 25°C)
Dimensioning of RCE and CCE can be done in three steps:
1. Calculate the maximum forward voltage from the
datasheet of the used IGBT and determine VCEstat
2. Calculate approximate value of RCE according to
equation (1) or (1.1) from VCEstat or determine RCE by
using fig.4.
3. Determine tmin and calculate CCE according to
equations (2) and (3).
Typical values are
for 1200 V IGBT: VCEstat = 5 V; tmin = 1,45 μs,
RCE = 18 kΩ, CCE = 330 pF
for 1700 V IGBT: VCEstat = 6 V; tmin = 3 μs,
RCE = 36 kΩ, CCE = 470 pF
Adaptation to 1700 V IGBT
When using 1700 V IGBTs it is necessary to connect a
1kΩ / 0,4 W adaptation resistor between the VCE-terminal
(S20/ S1) and the respective collector.
0
1
2
3
4
5
6
7
8
10 20 30 40 50
RCE / kOhm
VCEstat / V
1200V (min)
1200V (typ)
1200V (max)
1700V (min)
1700V (typ)
1700V (max)