Side-by-side comparison
| Parameter | IGBT | SCR Power Switch |
|---|---|---|
| Device Structure | IGBT — BJT output stage + MOSFET input stage (4-terminal equivalent) | SCR — 4-layer PNPN thyristor structure |
| Turn-ON | Gate voltage > V_GE(th) (~5–7 V); remains on only while gate held high | Gate current pulse triggers; latches ON until I_A < I_H |
| Turn-OFF | Remove gate signal; turns off in t_off ~ 0.5–3 µs | Current must fall below I_H; forced commutation in DC circuits |
| Maximum Switching Frequency | 1–50 kHz (standard); up to 150 kHz (trench-gate) | 50 Hz – 1 kHz; turn-off time 10–100 µs limits frequency |
| Voltage Rating (commercial) | Up to 6500 V (Infineon FZ1500R65KE3) | Up to 8000 V (ABB 5STP 45 series) per device |
| Current Rating (commercial) | Up to 3600 A (IGBT module) | Up to 5000 A per device |
| On-State Voltage Drop | V_CE(sat) ≈ 1.5–3 V at rated current | V_T ≈ 1.5–2 V — similar, slightly lower at high current |
| Gate Drive Complexity | Isolated ±15 V gate drive (e.g. ACPL-332J optocoupler) | Minimal — 50–100 mA pulse, 1–5 µs wide |
| Reverse Voltage Blocking | No — anti-parallel diode is standard; asymmetric IGBT blocks reverse | |
| Yes — inherent reverse blocking in standard SCR | ||
| Application | VFDs, UPS, solar inverters, induction heating | HVDC valves, AC phase controllers, soft starters, cycloconverters |
Key differences
The IGBT's defining advantage over the SCR is full gate-controlled turn-off: remove the gate signal and the device turns off in 1–3 µs, enabling PWM at up to 50 kHz. The SCR latches once triggered and cannot be turned off by the gate — in DC circuits a separate LC commutation circuit is required, adding size and failure modes. SCRs reach 8 kV per device, making them irreplaceable in HVDC converter valves where stacks of 50–100 thyristors in series handle hundreds of kilovolts. IGBTs do not approach those voltages per device and their switching frequency advantage is irrelevant at 50 Hz line-frequency converters. In the 600 V–3300 V, 1 Hz–20 kHz region, the IGBT has completely displaced the SCR.
When to use IGBT
Use an SCR when operating at line frequency (50–60 Hz), controlling very high voltages (above 3 kV per device), or where latching behaviour reduces drive complexity in AC phase controllers. Example: a 200 kW AC soft starter for a 415 V induction motor uses six BT152 SCRs in anti-parallel pairs; the thyristors fire once per half cycle and commutate naturally at the current zero crossing.
When to use SCR Power Switch
Use an IGBT when PWM switching above 1 kHz is required, the load is a DC circuit, or the drive must produce controllable output voltage with low harmonics. Example: a Mitsubishi CM300DY-24NF IGBT module switching at 10 kHz in a 45 kW VFD (Yaskawa A1000) produces < 5% THD on the motor terminals.
Recommendation
For any inverter, chopper, or DC motor drive application, choose the IGBT — controllable turn-off and high switching frequency make it the only viable option. Reserve SCRs for AC phase control, cycloconverters, and HVDC valves where line-frequency commutation and extreme voltage ratings are needed. There is no meaningful competition for PWM applications: the SCR cannot do what an IGBT does.
Exam tip: Examiners ask students to compare the turn-off process of an IGBT and an SCR and explain forced commutation — know that IGBT turns off by removing gate drive (tail current lasts 1–3 µs), while SCR requires current to drop below I_H or an external LC circuit to reverse anode current briefly.
Interview tip: A placement interviewer at a drives or FACTS manufacturer will ask why IGBTs replaced SCRs in VFDs while SCRs remain in HVDC — answer: IGBTs offer gate-controlled turn-off enabling PWM, but per-device voltage ceiling is ~6.5 kV; SCRs reach 8 kV and commutate naturally at 50 Hz, so they remain in HVDC and large cycloconverters.