Testing IGBTs

We were asked the other day whether our curve tracer CTR-101 can test IGBT devices.

What’s an Insulated Gate Bipolar Tranistor (IGBT)? If you live in a world of small analog signals (that’s us), then you probably haven’t used an IGBT. But if you work in high power applications such as variable speed drives for induction motors or welding controllers, you’ve probably used them.

The IGBT is one of those hybrid devices that is ‘the best of both worlds’. It combines the high input impedance of the MOSFET with the low saturation voltage of the bipolar transistor.  The IGBT is used almost exclusively as a switching device, so in the ON state, the power dissipation is proportional to the saturation voltage.  Smaller saturation voltage results in less power dissipation and simplified cooling requirements.

We ordered some of the IGBT model IRG4PF50 to test on the curve tracer. The specifications are impressive: 900 volt breakdown voltage, 51 amps current, 200 watts, all for $6.00 USD
$7.90 CAD
 from Digikey.  Even allowing for the limitations of heatsinks and thermal resistance (which always make the actual power less than shown on the spec sheet), this is an impressive device.

The CTR-101 can measure up to 30 volts or so at a test current of 1 ampere: it’s intended for small signal devices.  But we can test the behaviour in the small signal region.  This would be useful, for example, if you needed to match one or more units.

The figure shows the results: on the N-MOSFET setting of the curve tracer, we get a family of curves similar to an enhancement mode MOSFET.  There is certainly enough information here to determine the gate threshold voltage and match device characteristics.  So yes, the CTR-101 can measure the characteristics of an IGBT.

A transfer characteristic (drain current vs gate-source voltage) might also  be useful: if you have some interest in that, give us a shout and we’ll add that feature to the software.

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