The term Igbt is an acronym for Insulated Gate Bipolar Transistor. It can be thought of as a Transistor with a Mosfet front end. It has three terminals (or leads) labeled Gate, accumulator and Emitter. Some Igbt's have a built in security diode. This diode is linked across the accumulator and Emitter terminals. It is added for transient voltage security when the Igbt is switching Inductive loads.
When these devices are determined 'suspect' it is valuable to validate their execution through a functional test procedure. One of two methods can be used:
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The first test method will validate the condition of the security diode, and the resistance of the accumulator 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 accumulator and Emitter terminals when the device is stressed.
To accomplish this test will wish 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 accumulator 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 accumulator Terminal. Confirm an open circuit condition (Igbt without a security diode). If the Dvm displays a transmit 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 normal test conditions and are used to confirm whether the Igbt has a security diode, and if it does, whether it is functional or not.
The second test method will check the Igbt's functionality, by gating the device. To accomplish this test will wish an Igbt Tester. Confirm that the device tests as follows:
Attach the Igbt Tester leads to the Gate, accumulator 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 accumulator 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 normal 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 normal test condition for this type of device.
It is important to note that Functional test of the Igbt should always be performed when the device is out-of-circuit. In other words, it should be removed from the goods and have no other electrical connections in place, other than those outlined in the Test procedure.
Igbt Test Procedures
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