Why Snubber Selection Deserves Care

When an IGBT switches off a high current, the energy stored in the commutation-loop inductance produces a voltage spike across the device, and if the spike exceeds the rating the IGBT can fail. A snubber capacitor close to the module absorbs that energy and limits the overshoot, so its selection is a reliability decision. This guide gives a repeatable method for selecting a TDK EPCOS snubber capacitor.

Step 1: Fix the Voltage Class

Choose the voltage class with margin above the worst-case DC-link voltage plus the expected overshoot, because the capacitor must survive the transients it is there to absorb. TDK EPCOS snubber capacitors cover 850 V to 2000 V DC, so a class fits every common high-power IGBT stage. A higher rating costs more and takes a larger case, so choose the lowest class that covers the worst case with margin.

Step 2: Size the Capacitance

Size the capacitance to absorb the energy stored in the commutation-loop inductance at the switching current, so the resulting voltage rise stays within the IGBT rating. The exact value depends on the loop inductance and the current, and the low-ESL construction of the part determines how much of that energy it can absorb in the time of a switching edge. Our FAE team can help with the calculation and validate the result on the bench.

Step 3: Minimize the ESL

The defining parameter of a snubber is its equivalent series inductance, because the snubber must respond within a fast edge. TDK EPCOS offers parts with ESL as low as about 6 nH, which makes them effective at the high dV/dt of modern IGBTs and wide-bandgap devices. Lower ESL means the snubber acts sooner and the overshoot is smaller, so choose the lowest ESL that fits your voltage and capacitance, and keep the snubber loop short so the low ESL actually helps.

Step 4: Match the Terminal Configuration

The snubber mounts directly across the IGBT module, so the terminal configuration, the hole spacing and the height must match the module. TDK EPCOS offers many configurations with hole spacings from 19.5 mm to 63 mm, so a capacitor can be matched to common high-power modules. The strap terminals are tin-plated copper for a reliable, low-inductance contact.

Step 5: Validate on the Bench

After selection, measure the IGBT collector-emitter overshoot with and without the snubber at the worst-case current and DC-link voltage. A well-chosen snubber reduces the overshoot by a significant margin and improves the EMC of the converter at the same time. Our FAE team can review the waveforms and help interpret them.

Getting Help

If you send your IGBT module, DC-link voltage and switching current to our FAE team, we will propose a snubber with the right capacitance, voltage and terminal configuration and support the layout. BeiLuo holds mainstream TDK EPCOS snubber capacitors in regional stock and ships them with import declaration, certificate of origin and RoHS documents.