Double Pulse Measurements And Current Sensing; High Resistance Shunt; Two Stage Current Transformer - Wolfspeed SPEEDVAL KIT HALF-BRIDGE MOD-MB-HB-0900V-40A User Manual

5. DOUBLE PULSE MEASUREMENTS AND CURRENT SENSING

This section shows how to set up the SpeedVal Kit platform to take accurate switching energy
measurements using a double pulse test (DPT). Each power daughter card comes with a current shunt
for sensing I , but the resistance value with which it comes preinstalled may be optimized for power
DS
testing rather than switching energy measurements. This is because the overall shunt resistance must
be kept very low (≤10 mΩ) to keep power dissipation to a minimum when running power tests.
The power daughter card may need the current sense circuit to be modified before taking switching
energy measurements. There are two acceptable modifications to support accurate switching energy
measurements. Consult the user guide of the selected power daughter card to determine what value
shunt resistors are preinstalled and to review the procedure to change the value if necessary.

5.1. HIGH RESISTANCE SHUNT

One method for accurate switching loss measurements is to use a shunt with a relatively high
shunt resistor value. Many daughter cards have eight (0603 footprint) shunt resistors. Setting
these resistors to 1 Ω each gives an overall shunt resistance of 125 mΩ and very good signal-to-
noise ratio for taking accurate switching loss measurements. The RC filter network may need to
be modified from the preinstalled values as well. The typical shunt circuit and filter components
for DPT are shown in Figure 20. Consult the power daughter card manual for the board being
tested to see the specific component designators that may need to be modified. The system
should not be run in a continuous power test with this configuration, as the power rating of the
resistors is not sufficient to support operation beyond DPT.
Shunt
8x1Ω

5.2. TWO STAGE CURRENT TRANSFORMER

Another current sensing method is to implement a two-stage current transformer. The first stage
consists of a 1:10 turn surface mount transformer that is included with the motherboard kit
which must be soldered onto the power daughter card. The daughter card comes prepopulated
with surface mount shunt resistors, which must be removed to populate the current transformer.
There is also a RC compensation network and MMCX connector that must be removed as well.
PRD-06829 REV. 1, December 2022
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sponsorship or association.
20
F 20: H R
IGURE IGH ESISTANCE
SpeedVal Kit™ Half-Bridge User Guide
Scope Input
50
100pf
S C
HUNT IRCUIT
26