IGBT (insulated gate bipolar transistor) :
An IGBT is a new development in power semiconductor devices that possess the advantages of both MOSFET and BJT. It is a voltage-controlled bipolar device that has emitter-collector characteristics of BJT and control features of MOSFET. The below shows the structure of IGBT which consists of four alternate p-n-p-n layers with three terminals source or emitter, drain or collector, and gate.
When a positive voltage signal more than the threshold value is applied across the gate and emitter, IGBT is turned ON. Once the gate voltage is removed the IGBT gets turned OFF. Thus the gate terminal has full control over the operation of the IGBT.
Since IGBT exhibits emitter-collector characteristics of BJT, the ON-state voltage drop of IGBT will be very low similar to BJT. It has high input impedance and a simple gate drive circuit similar to MOSFET. Due to their ruggedness, capability, peak current, and ease of gate drive IGBTs become the most favored power semiconductor device in many applications.
MOSFET (metal oxide semiconductor field effect transistor) :
A MOSFET is a unipolar three/four-terminal voltage-controlled device. It has four terminals source (s), gate (g), drain (d), and body (b) as shown below. The flow of current in MOSFET is due to majority carriers (either electrons or holes) unlike both electrons and holes as seen in IGBT, hence MOSFET is a unipolar device.
In order to turn ON the MOSFET, a gate signal is to be applied across the gate-source terminals. Since the MOSFET is a voltage-controlled device, it requires only a small input current, and the flow of current between its source and drain terminals is controlled by the positive voltage signal applied to the gate terminal.
Similar to IGBT by removing the gate-source voltage signal, the MOSFET can be turned OFF. MOSFETs can be turned ON and turned OFF very quickly, they operate at very high frequencies.
However, MOSFETs are sensitive to electrostatic discharge and are difficult to protect under short-circuit conditions. Also due to the high ON-state resistance of MOSFET, the conduction losses are high compared to IGBT, hence they are used for low-power applications.
Comparison Between IGBT and MOSFET :
| Particulars | MOSFET | IGBT |
|---|---|---|
| Definition | A MOSFET is a type of field effect transistor with either N-channel or P-channel. It is a unipolar device in which conduction takes place due to majority carriers i.e., due to electrons in N-Channel MOSFETs and holes in P-Channel MOSFETs. | An IGBT is a combination of both MOSFET and BJT. It is a bipolar device in which conduction takes place due to the movement of both minority and majority charge carriers i.e., electrons and holes. |
| Symbol |  |  |
| Full Form | Metal Oxide Semiconductor Field Effect Transistor | Insulated Gate Bipolar Transistor |
| Type of Drive | It is a voltage-controlled device. | It is also a voltage-controlled device. |
| Terminals | The terminals of MOSFET are gate (G), source (S), and drain (d). | The terminals of IGBT are gate (G), source (s) or emitter (e), and drain (d) or collector (c). |
| Operating frequency | High (up to few MHz) | Low (up to few kHz) |
| Cost | Low | High |
| Voltage Blocking Capacity | Less | High |
| Saturation voltage | High | Low |
| Input Impedance | High | High |
| Output Impedance | High | Low |
| Switching Losses | Low | High |
| Conduction Losses | High | low |
| Voltage Handling Capacity | Low | High |
| Current Handling Capacity | High | High |
| Electrostatic Discharge | Sensitive | Comparatively less sensitive |
| Turn OFF time | Small | Large |
key Differences Between IGBT and MOSFET :
- Both IGBT and MOSFET are popular semiconductor devices used for switching and amplifying electronic signals. IGBT has the combined properties of BJT and MOSFET. It has input characteristics of MOSFET which offers a simple gate drive and output characteristics of BJT which has low ON-state voltage drop. Whereas MOSFET is a type of field effect transistor where current flow is due to the movement of majority carriers.
- An insulated gate bipolar transistor as terminals namely source or emitter, drain or collector, and gate. Whereas a metal oxide semiconductor field effect transistor (MOSFET) is actually a four terminal device namely source, drain, gate, and body. But mostly MOSFET is used as a three-terminal device by connecting the body to the source terminal.
- IGBTs have high-voltage and high-current handling capabilities they are used in high-power circuits. Whereas the power handling capacity of MOSFETs is low as compared to IGBTs.
- The operating frequency of IGBTs (up to a few kHz) is less than compared to the operating frequency of MOSFET (up to a few MHz).
- Both IGBTs and MOSFETs are voltage-controlled devices i.e., the output current of the device is controlled by the voltage at the input terminal.
- Due to conductivity modulation, the ON-state voltage drop of IGBT is low as compared to MOSFET. Thus IGBT has superior ON-state current density.
- IGBTs are somewhat more expensive than MOSFETs. Though they are a bit costlier, a simple gate drive requirement and low conduction losses make them efficient in various circuits.
- The IGBTs are used in various electronics circuits like SMPS, UPS, ac motor controllers, welding, etc. The applications of MOSFET are switching and amplifying electronic signals, inverters, chopper circuits, etc.