How it works
An insulated gate controls a bipolar current path. Minority-carrier injection reduces conduction loss at useful high-voltage/current operating points, but stored charge produces turn-off tail current. This creates a real tradeoff between on-state voltage and switching energy. Frequency recommendations belong to a specific generation and duty cycle, not to the letters “IGBT” alone.
An insulated gate controls the collector-to-emitter power path. This functional diagram omits the detailed structure, capacitances and any separate freewheel diode.
Parameters that matter
- On-state voltage
- VCE(sat) changes with collector current, gate voltage and junction temperature. Model its curve instead of treating it as a fixed diode drop.
- Switching energy
- Eon/Eoff must retain test bus, current, gate resistance and temperature. Tail current makes turn-off loss particularly relevant.
- Companion diode
- A co-pack diode is a separate die with its own current, recovery and thermal limits. Some IGBTs have no diode; reverse-conducting types are another category.
- Fault withstand
- Short-circuit withstand and turn-off SOA need explicit evidence. A large pulse-current rating alone does not establish either.
A worked selection example
Illustrative calculation · not a product guarantee
See what doubling frequency does to loss
Hypothetical repetitive test point: 20 A, 50% conduction duty, 2.0 V on-state drop and 1.5 mJ total switching energy at the actual bus and temperature. Assume switching energy remains unchanged when comparing 10 kHz and 20 kHz.
- Approximate conduction loss: I × VCE(sat) × duty = 20 × 2.0 × 0.5 = 20 W.
- At 10 kHz, switching loss is 1.5 mJ × 10 kHz = 15 W.
- At 20 kHz, the same switching energy produces 30 W. This simplified comparison excludes diode, driver and load-current modulation losses.
- For a motor inverter, integrate losses over sinusoidal current and the actual PWM pattern before selecting the heatsink.
Frequency can change the thermal result substantially even when conduction conditions look unchanged. Validate with hot device curves and the real modulation.
Where it fits
Suitable starting points
- Industrial inverters, welders, UPS and selected PFC/charger stages where conduction, switching frequency and system cost align.
Where to take extra care
- Generally unsuitable as the first choice for low-voltage battery switching or very-high-frequency conversion. Do not infer short-circuit rating from an application headline.
Series directions to investigate
Silan SGT includes field-stop and application-speed variants; SGT25U120FD1P7 is a documented TO-247-3L example with a co-pack diode. JSMC lists discrete and module directions. Match circuit configuration, isolation, diode and terminal geometry before comparing price.
What Chinese suppliers can offer
Where the opportunity lies
Chinese manufacturers’ discrete, IPM and module ranges create practical options for established appliance and industrial drive architectures. A module may reduce assembly work, but its gate interface, NTC, isolation and power-cycling duty must fit. Compare completed-stage cost and validation effort.
What still needs evidence
Confirm the exact manufacturing source, current datasheet, sample results and commercial terms before placing an order. Series availability does not establish qualification for your application.
Questions for the supplier
- 01
Hot output curves and energy curves at the proposed Rg and bus.
- 02
Diode current/recovery data separately from IGBT data.
- 03
Short-circuit/protection conditions when required, module power cycling, isolation test and mounting specification.
Technical references
These references support the principles and catalogue directions discussed here. Public documentation is a different evidence level from a supplier reply, a lot document or an independent test. This guide does not claim those later stages have been completed.
- 1. Difference between MOSFET and IGBT
- 2. Explanation of discrete IGBTs datasheets
- 3. SGT25U120FD1P7 datasheet, Rev 1.1
- 4. Product catalog
- 5. Superjunction MOSFET selector
These guides explain selection principles. Final decisions require the current datasheet for the exact ordering code, operating conditions and appropriate application testing.