The term Igbt is an acronym for Insulated Gate Bipolar Transistor. It can be plan of as a Transistor with a Mosfet front end. It has three terminals (or leads) labeled Gate, collector and Emitter. Some Igbt's have a built in security diode. This diode is connected over the collector and Emitter terminals. It is added for transient voltage security when the Igbt is switching Inductive loads.
When these devices are thought about 'suspect' it is vital to validate their carrying out straight through a functional test procedure. One of two methods can be used:
The first test formula will validate the health of the security diode, and the resistance of the collector and Emitter terminals. It is not a definitive test, but will find 80% of all faulty devices. This is due to the fact that most faulty Igbt's show a low resistance or short over the collector and Emitter terminals when the device is stressed.
To achieve this test will require a Dvm (Digital-Volt-Meter). Set the Dvm to the Diode Test position, and confirm that the device tests as follows:
Attach the Red Lead of the Dvm to the collector concluding and Black Lead to the Emitter Terminal. Confirm an open circuit condition.
Attach the Red Lead of the Dvm to the Emitter concluding and Black Lead to the collector Terminal. Confirm an open circuit health (Igbt without a security diode). If the Dvm displays a send voltage drop of 0.2 to 0.8 Vdc it means that the Igbt has a built in security diode. Both of these results are general test conditions and are used to confirm either the Igbt has a security diode, and if it does, either it is functional or not.
The second test formula will check the Igbt's functionality, by gating the device. To achieve this test will require an Igbt Tester. Confirm that the device tests as follows:
Attach the Igbt Tester leads to the Gate, collector and Emitter Terminals. Confirm that the device Conduction Led is not lit.
Press the Test Button, and confirm that the Conduction Led lights.
Reverse the collector and Emitter leads. Do not press the Test Button. If the Conduction Led lights the Igbt has a built in security diode. This is a general test health for this type of device. If the Conduction Led does not light then the Igbt does not have a built in security diode. This is also a general test health for this type of device.
It is important to note that Functional test of the Igbt should all the time be performed when the device is out-of-circuit. In other words, it should be removed from the product and have no other electrical connections in place, other than those outlined in the Test procedure.
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