Infineon EVAL-IH-R5IPB-A-V1, Руководство пользователя, Страница: 14 / 34

EVAL-IH-R5IPB-A-V1 Evaluation board
User Guide
Usage
the turn-on point of the IGBT (as shown in Figure 8a). It is recommended to change the value of the resistance
only if the value of the resonant capacitance is changed.
4.1.4 Tuning collector-current sense network
The IEWS20R5135IPB for induction heating also features an overcurrent protection functionality that allows the
IGBT to be switched off as soon as the collector current reaches a selected threshold. Such a functionality
requires a voltage replica of the collector current, available at the CS pin. Such a voltage signal has to be as clean
as possible in order to avoid unpredictable behavior of the IGBT
1
.
The evaluation board utilized a 10 m Ω SMD metal-film resistor as sensing element of the collector current,
followed by a passive low-pass filter, as shown in Figure 9a. The DC gain of the low-pass filter determines the
current at which the IGBT is shut down. By means of the R
CS
resistance, the gain can be changed, thus changing
the maximum current that can flow in the IGBT. Figure 9b shows the measured dependence of the maximum
collector current on the value of the resistance RCS. The dependence is not perfectly linear, as at higher RCS the
effect of the capacitance in parallel becomes more prominent.
In Figure 9c, a comparison is shown between the collector current measured by the Rogowski coil and the voltage
measured among CS and emitter pins of the IEWS20R5135IPB. It can be noticed that during the on-time of the
IGBT, where the collector current is almost linearly increasing, the voltage at the CS pin (green curve) replicates
the current measured with the Rogowski coil (yellow curve). During the off-time, the collector current is almost
zero
2
, but V
CS
shows similar behavior like the V
CE
(see Figure 11). This behavior is caused by the parasitic
capacitance of the package that creates a coupling between the collector potential and the CS potential. Such
behavior, however, does not affect the IEWS20R5135IPB operation, since the coupling is present only in the off-
state of the IGBT.
1
The threshold of the current sense limitation is set to a typical value of -200 mV. The resistor divider of the low pass filter in Figure 9a is
chosen so that for the designed peak current, the voltage at CS is equal to -200 mV.
2
The offset of the I
C
in the off-state is due to the AC nature of the Rogowski probe.
Application Note 14 of 34 V 1.1
2019-11-25