IGBT vs. MOSFET: A Practical Selection Guide
IGBTs and MOSFETs are the two most common power switches, but they have different characteristics. Choosing the right one is key to an efficient and reliable design.
1. Operating Principle
A MOSFET is a voltage-controlled device that behaves like a resistor when on. An IGBT combines the simple gate drive of a MOSFET with the high-current and low-saturation-voltage capability of a bipolar transistor.
MOSFET
Voltage-controlled device with resistive conduction characteristics. Best for high-frequency and low-voltage applications.
IGBT
Combines MOSFET gate drive with bipolar conduction. Ideal for high-voltage, high-current applications.
2. Switching Speed
MOSFETs are the clear winners here. They can switch at frequencies of several hundred kHz, or even into the MHz range. IGBTs are generally limited to frequencies below 100 kHz due to their "tail current" during turn-off.
| Device | Typical Switching Frequency | Best Applications |
|---|---|---|
| Low-Voltage MOSFET | 100 kHz - 1 MHz+ | DC-DC converters, SMPS |
| High-Voltage MOSFET | 50 - 200 kHz | LED drivers, adapters |
| IGBT | 1 - 50 kHz | Motor drives, inverters |
3. Voltage and Current Ratings
IGBTs typically handle higher voltages and currents. While high-voltage MOSFETs exist, IGBTs are generally more cost-effective for applications above 600V and tens of amps.
4. Conduction Loss
At low currents, MOSFETs have lower conduction losses due to their resistive nature (Rds(on)). At high currents, the fixed saturation voltage (Vce(sat)) of an IGBT results in lower conduction losses.
| Characteristic | MOSFET | IGBT |
|---|---|---|
| Gate Drive | Simple voltage drive | Simple voltage drive |
| Conduction Loss (Low Current) | Lower (I x Rds(on)) | Higher |
| Conduction Loss (High Current) | Higher | Lower (I x Vce(sat)) |
| Switching Speed | Very Fast | Moderate |
| Voltage Rating | Up to ~900V | 600V - 6500V+ |
| Cost (High Voltage) | Higher | Lower |
5. Conclusion: Which to Choose?
Use a MOSFET for:
- High-frequency applications (SMPS, DC-DC)
- Low-voltage applications (below 200V)
- Applications requiring fast switching
- Low to medium current applications
Use an IGBT for:
- High-power applications (motor drives)
- High-voltage applications (above 600V)
- Lower-frequency switching (below 50kHz)
- High-current applications (>10A)
6. Selection Decision Tree
- Determine Voltage Requirement If >600V, strongly consider IGBT. If <200V, MOSFET is usually better.
- Evaluate Switching Frequency If >100kHz required, MOSFET is typically the only option.
- Calculate Current Requirements For high current (>20A) at high voltage, IGBT usually wins on conduction losses.
- Consider Cost Constraints At high voltages, IGBTs are generally more cost-effective.
- Evaluate Thermal Requirements Compare total losses (conduction + switching) for your specific operating conditions.