An IGBT (insulated-gate bipolar transistor) is a power semiconductor that power electronics use as a fast electronic switch for high voltage and high current. Whether it suits a design is decided by a handful of datasheet ratings: blocking voltage, current rating, conduction loss, switching loss, junction temperature and short-circuit withstand. Knowing what those numbers mean helps DC charger buyers ask better questions about efficiency, heat and reliability.
Key Takeaways
- An IGBT is a high-power switch; its datasheet ratings define where it fits.
- VCES, IC, VCE(sat), switching energy and junction temperature work together.
- Heat and thermal cycling drive long-term reliability.
- DC charger buyers should ask about efficiency, derating, protection and module service.
The Ratings That Define an IGBT
Terminology, letter symbols and measurement methods for discrete IGBTs are set out in IEC 60747-9. Module datasheets use the same core terms:
| Symbol | Meaning | Why it matters |
|---|---|---|
| VCES | Maximum collector-emitter blocking voltage | Must exceed the converter’s DC bus voltage plus spikes, with margin |
| IC | Continuous collector current at a stated case temperature | Real usable current is lower at higher temperatures |
| VCE(sat) | Voltage drop when fully on | Sets conduction loss; lower means less heat at a given current |
| Eon, Eoff | Energy lost in each turn-on and turn-off | Multiplied by switching frequency, this gives switching loss |
| Tvj max / Tvj op | Maximum and operating junction temperature | Defines how hard the cooling system must work |
| tsc | Short-circuit withstand time | Time the gate driver has to detect a fault and switch off |
| Rth(j-c) | Thermal resistance, junction to case | How easily heat leaves the chip toward the heat sink |
Reading the Numbers Together
No single rating tells the whole story. A few practical rules of thumb:
- Current ratings are conditional. IC is quoted at a specific case temperature. In a sealed charger cabinet on a hot day, the usable current is lower, so designers derate.
- Conduction and switching loss trade off. Devices optimized for low VCE(sat) often switch more slowly, and fast-switching devices often have a higher on-state drop. The best choice depends on the converter’s switching frequency.
- Total loss becomes heat. Conduction loss plus switching loss, divided by the thermal path to air or coolant, sets the junction temperature. Higher temperature shortens the life of solder joints and bond wires through thermal cycling.
- Voltage margin protects against spikes. Fast current changes in stray wiring inductance create overshoot, so blocking voltage is chosen well above the nominal bus.
Discrete Devices vs Power Modules
Low-power converters often use discrete IGBTs in plastic packages on a shared heat sink. Higher-power equipment uses modules that combine several IGBT chips and freewheeling diodes on an insulated base plate, sometimes with a built-in temperature sensor. Modules simplify assembly and cooling but must be matched to a suitable gate driver. Wide-bandgap devices such as silicon carbide MOSFETs compete with IGBTs in some charger stages; the U.S. Department of Energy notes that today’s vehicle power electronics are largely silicon-based, with wide-bandgap materials under active development.
Questions DC Charger Buyers Can Ask
AC wallboxes pass grid power to the car’s onboard charger, so IGBT ratings matter mainly in DC fast chargers and their power modules. Our explainer on how DC fast chargers work shows where these stages sit. When comparing DC units, ask:
- What efficiency is achieved at full and partial load, and at what ambient temperature?
- How are the power modules cooled, and what is the derating curve above a given ambient temperature?
- How does the unit protect against short circuits and overtemperature?
- Can a failed power module be replaced in the field, and how long are spares supported?
These factors also show up in the unit cost of an OEM charger. Reading the full product sheet is covered in our guide on how to read an EV charger datasheet.
EVDANCE offers the EV-RHDC30K-L compact DC fast charger (22 kW DC, OCPP 1.6J, IP54) for sites that need DC charging. Our team can discuss thermal design, service and spare parts through our commercial charging solutions.
Frequently Asked Questions
What does “1200 V IGBT” mean?
It usually refers to VCES, the maximum voltage the device can block when off. It is not the voltage it should run at continuously; designers leave margin.
Why do IGBT modules fail?
Common causes include overheating, repeated thermal cycling that fatigues internal joints, voltage spikes and short circuits not cleared fast enough. Good cooling and protection reduce these risks.
Does a higher current rating mean a better charger?
Not necessarily. A well-cooled design with sensible margins can outlast an overrated device running hot. Ask about efficiency, derating and field service.
Related Reading
- How Fast Is a DC Fast Charger?
- Why Is DC Fast Charging So Expensive?
- Commercial EV Charger Maintenance Checklist
