SCALE™-2 1SC0450E2B0
Preliminary Description & Application Manual
www.power.com/igbt-driver
Page 15
Active Clamping (ACL)
Active clamping is a technique designed to partially turn on the power semiconductor as soon as the
collector-emitter voltage exceeds a predefined threshold. The power semiconductor is then kept in linear
operation.
Basic active clamping topologies implement a single feedback path from the IGBT’s collector through
transient voltage suppressor devices (TVS) to the IGBT gate. The 1SC0450E2B0 supports Advanced Active
Clamping from Power Integrations, where the feedback is also provided to the driver’s secondary side at pin
ACL (Fig. 6): as soon as the voltage at pin ACL exceeds about 1.3V, the turn-off MOSFET is progressively
switched off in order to improve the effectiveness of the active clamping and to reduce the losses in the
TVS. The turn-off MOSFET is turned completely off when the voltage at pin ACL approaches 20V (measured
to COM).
It is recommended to use the circuit shown in Fig. 6. The following parameters must be adapted to the
application:
For TVS D
1
, D
2
it is recommended to use:
-
3300V IGBTs with DC-link voltages up to 2200V: Seven unidirectional 300V TVS and one
bidirectional 350V TVS. Good clamping results can be obtained with seven unidirectional TVS
P6SMB300A and one bidirectional TVS P6SMB350CA from Diotec.
-
4500V IGBTs with DC-link voltages up to 3200V: Eight unidirectional 400V TVS and one
bidirectional 350V TVS. Good clamping results can be obtained with eight unidirectional TVS
P6SMB400A and one bidirectional TVS P6SMB350CA from Diotec.
-
6500V IGBTs with DC-link voltages up to 4350V: Ten unidirectional 440V TVS and one
bidirectional 440V TVS. Good clamping results can be obtained with ten unidirectional TVS
P6SMB440A and one bidirectional TVS P6SMB440CA from Diotec.
At least one bidirectional TVS (D
1
) (≥300V for 3300V IGBTs, ≥350V for 4500V IGBTs, ≥440V for
6500V IGBTs) must be used in order to avoid negative current flowing through the TVS chain during
turn-on of the anti-parallel diode of the IGBT module due to its forward recovery behavior. Such a
current could, depending on the application, lead to under-voltage of the driver secondary-side
voltage VISO to VE (15V).
Note that it is possible to modify the number of TVS in a chain. The active clamping efficiency can
be improved by increasing the number of TVS used in a chain if the total breakdown voltage remains
at the same value. Note also that the active clamping efficiency is highly dependent on the type of
TVS used (e.g. manufacturer).
D
3
and D
4
: It is recommended to use Schottky diodes with blocking voltages >35V (>1A depending on
the application).
Please note that the diodes D
3
and D
4
must not be omitted if Advanced Active Clamping is used.
If active clamping is not used, the diode D
4
can be omitted. The pin ACLx must then be left open.
Gate turn-on (GH) and turn-off (GL) terminals
These terminals allow the turn-on (GH) and turn-off (GL) gate resistors to be connected to the gate of the
power semiconductor. The GH and GL pins are available as separated terminals in order to set the turn-on
and turn-off resistors independently without the use of an additional diode. Please refer to the driver data
sheet /3/ for the limit values of the gate resistors used.
A resistor between GL and COM of 6.8kΩ (other values are also possible) may be used in order to provide a
low-impedance path from the IGBT gate to the emitter even if the driver is not supplied with power. No
static load (e.g. resistors) must be placed between GL and the emitter terminal VE.