The term Igbt is an acronym for Insulated Gate Bipolar Transistor. It can be belief of as a Transistor with a Mosfet front end. It has three terminals (or leads) labeled Gate, assembler and Emitter. Some Igbt's have a built in security diode. This diode is linked across the assembler 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 requisite to validate their doing through a functional test procedure. One of two methods can be used:
The first test recipe will validate the condition of the security diode, and the resistance of the assembler 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 across the assembler and Emitter terminals when the gismo 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 gismo tests as follows:
Attach the Red Lead of the Dvm to the assembler terminal and Black Lead to the Emitter Terminal. Confirm an open circuit condition.
Attach the Red Lead of the Dvm to the Emitter terminal and Black Lead to the assembler Terminal. Confirm an open circuit condition (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 recipe will check the Igbt's functionality, by gating the device. To achieve this test will require an Igbt Tester. Confirm that the gismo tests as follows:
Attach the Igbt Tester leads to the Gate, assembler and Emitter Terminals. Confirm that the gismo Conduction Led is not lit.
Press the Test Button, and confirm that the Conduction Led lights.
Reverse the assembler 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 condition 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 condition for this type of device.
It is important to note that Functional test of the Igbt should all the time be performed when the gismo 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.
