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High Amplitude Arbitrary/Function Generator Simplifies Measurement in Automotive, Semiconductor, Scientific and Industrial Applications Application Note

Figure 9. Switching waveforms of an IGBT.

To optimize the design of an IGBT gate drive, the design engi- neer must understand the device's switching characteristics under the actual load conditions. To analyze these switching characteristics, the gate of the IGBT is stimulated with a series of single pulses while the gate-to-emitter voltage, collector-to-emitter voltage and collector current are meas- ured with an oscilloscope. Thanks to its capability to generate pulses with high amplitudes, the arbitrary/function generator AFG3011 is ideally suited for this task. Since the IGBT's collector-to-emitter voltage has a very high dynamic range for inductive loads, the measurement requires a high-voltage differential probe. The gate-to-emitter voltage can be measured with a standard passive probe, and the collector current with a non-intrusive current probe.

Figure 9 shows the typical switching waveforms of an IGBT with inductive load. From these waveforms, the design engi- neer can determine the switching energy, on-state losses and

whether the IGBT is operating within the safe operating area. Based on the measurement data, the engineer can then determine whether the selected pulse repetition frequency, amplitude and edge transitions are adequate to achieve the design objectives. If adjustments are necessary, dedicated short-cut keys on the AFG3011 front panel provide direct access to all pulse parameters. They can then be conveniently modified via rotary knob or numerical keys free from timing glitches and without interrupting the test.

A variety of factors must be considered during the measure- ment, such as the propagation delay (skew), offset and noise inherent to the probes. The engineer will find it beneficial to use an oscilloscope with a software tool that takes care of the probe related issues, automatically calculates the switching power losses, and determines the safe operating area of the IGBT.



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