IGBT is a high-performance power semiconductor device commonly used in circuits driving high-power loads.
I. Operation Principle of IGBT
IGBT consists of two devices, MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) and BJT (Bipolar Junction Transistor). It combines the advantages of MOSFET and BJT, possessing high-voltage and high-current switching capabilities.
The operation principle of IGBT can be divided into four stages: conduction, turn-off, transition, and saturation.
- Conduction Stage: In the conduction stage, the gate-source voltage (V_GS) of IGBT is applied through a control voltage source, establishing the conductive layer in the MOSFET part. This causes the narrowing of the P-type base region, triggering the conduction of the NPN transistor.
- Turn-off Stage: When the control voltage source is disconnected, IGBT enters the turn-off stage. The conductive layer of MOSFET disappears, widening the P-type base region, blocking the conduction of the NPN transistor.
- Transition Stage: During the transition from conduction to turn-off or turn-off to conduction, transient currents occur between MOSFET and BJT. The duration of this transition stage is very brief and can be neglected.
- Saturation Stage: During conduction, when IGBT is in saturation, BJT operates in the saturation region, and the conductive characteristics of MOSFET dominate the current flow. During turn-off, MOSFET operates in the cut-off region, and BJT is in the cut-off state.
II. IGBT Driver Circuit
To ensure the proper switching and operation of IGBT, an appropriate driver circuit is required. The main goal of the IGBT driver circuit is to ensure a stable and fast conduction and turn-off process.
The IGBT driver circuit typically consists of the following main components: power supply, level shifter, isolator, drive current source, and protection circuit.
- Power Supply: IGBT has high power consumption requirements, necessitating a stable high-current power supply. This can be achieved using a DC power supply and filtering capacitors to meet the current requirements of IGBT.
- Level Shifter: Due to potential mismatches between the signal level of the main controller and the level of IGBT’s driver circuit, a level shifter is required to convert the signal level to a level suitable for IGBT. Level shifters are typically implemented using optocoupler isolation or level shift chips.
- Isolator: As there may be a high voltage difference between the driver circuit and the actual IGBT circuit, an isolator is used to ensure isolation between the driver circuit and control circuit. Isolators are commonly implemented using optocouplers or transformers.
- Drive Current Source: IGBT requires sufficient current for rapid charging and discharging, so an appropriate drive current source is needed. The drive current source usually consists of a MOSFET amplifier and constant current source in the driver circuit.
- Protection Circuit: During operation, IGBT may experience faults such as overvoltage or overcurrent, so a protection circuit is needed to ensure the safe operation of IGBT. Protection circuits typically include overvoltage protection, overcurrent protection, and over-temperature protection functions.
When designing an IGBT driver circuit, factors such as stability, response speed, and adaptability of the driver circuit need to be considered. Additionally, the selection of IGBT’s driver circuit should be based on specific applications to meet different operating conditions and requirements.
In conclusion, IGBT is a high-performance power semiconductor device controlled by a driver circuit. The IGBT driver circuit typically includes components such as a power supply, level shifter, isolator, drive current source, and protection circuit. Through thoughtful design and selection of the driver circuit, the stable and fast operation of IGBT can be ensured to meet various application requirements.