IGBT (The insulated-gate bipolar transistor)

The insulated-gate bipolar transistor or IGBT is a three-terminal power semiconductor device, noted for high efficiency and fast switching. The IGBT combines the simple gate-drive characteristics of the MOSFETs with the high-current and low–saturation-voltage capability of bipolar transistors by combining an isolated-gate FET for the control input, and a bipolar power transistor as a switch, in a single device. The IGBT is used in medium- to high-power applications such as switched-mode power supply, traction motor control and induction heating. Most of the centrifuge speed controls using IGBT.









The main advantages of the IGBT are:

1. Good Power handling capabilities.
2. Low forward conduction voltage drop of 2V to 3V, which is higher than for a BJT but lower than for a MOSFET of similar rating. 
3. This voltage will increase with the temperature. This property makes the device easy to operate in parallel without danger of thermal instability.
4. High speed switching capability.
5. Low gate current.
6. Relatively simple voltage controlled gate driver.

Important features of the IGBT:

1. Absence of secondary breakdown. 
2. So it has large Safe Operating Area (SOA) and low switching losses Only small snubbers are required.
3. Absence of body diode in IGBT. (Remember that Power MOSFET has the parasitic diode)
4. Separate diode must be added in anti-parallel when reverse conduction is required.

How to test IGBT using Multimeter:

1. Select Diode function in multimeter.
2. put negative terminal on the emitter and touch positive terminal with the collector. It's shouldn't give a reading.
3. Touch the positive terminal with gate for few seconds and put back on the collector. It's should give reading due to charge.
4. Touch both gate and emitter with your finger. Reading come to zero due to capacitor discharge. 
5. Repeat this few times. 
6. If results are positive IGBT works in order.