Application Note
6
Revision 1.0
2017-11-15
1200V HighSpeed 3 IGBT in TO-247PLUS Evaluation Board
User Manual
Hardware
An experimental analysis of a
device’s switching behavior requires oscilloscope measurements of the
gate voltage, the collector-emitter voltage as well as the collector current. While voltage measurements
are straightforward, current measurements are more difficult to do, particularly in the presence of steep
current slopes. This evaluation board contains a basic SMD shunt resistor solution. It gives an
impression of the collector current waveform but is not considered an ideal solution for high accuracy
measurements.
2.2
Recommended accessories
The introductory section already clarified which components are delivered with the evaluation board and
which are not. Although the board can be used for switching loss measurements right away, it is strongly
recommended to use additional components for the highest accuracy and signal quality.
Coaxial shunt
Performing oscilloscope measurements of an IGBT’s collector current waveform is typically a non-trivial
task, particularly during switching events where extremely steep current slopes of several Amperes per
nanosecond are reached. An ideal current measurement for this purpose would be non-invasive
– at
least it should not require significant changes of the circuit
– and have a very high bandwidth.
By default, this evaluation board contains a
50mΩ metal foil SMD shunt resistor and an RC low-pass
filter in order to suppress disturbances caused by parasitic circuit elements. Due to the substantial
filtering, this approach might be considered a current estimation rather than a measurement. For high
accuracy measurements it is recommended to use a coaxial shunt SDN-414-xxx.[3] It has a bandwidth in
the gigahertz range and can be connected to any oscilloscope with a standard BNC cable.
To assemble the coaxial shunt:
1. Unsolder the
50mΩ metal foil resistor R201 and the 100Ω thin film resistor R200 on the bottom side
of the board.
2. Optionally, remove the capacitor C201 and the probe adapter Id2 as they are inoperable.
3. Strip the isolation at the central terminal of the shunt and solder it to the PCB.
As visible in Figure 4, the shunt should be positioned as close to the PCB as possible to minimize
parasitic inductances.
(a)
(b)
Figure 4
Recommended accessories for switching loss measurements: (a) pictures of the
components, (b) assembly of the components on the board