© Fraunhofer IZM

Key Research Areas

Measuring switching losses in wide bandgap semiconductors under realistic conditions and without parasitic effects?

The traditional approach for measuring switching losses like double pulses relies on measuring the current in the semiconductor and the voltage drop at the point of switching. However, the parasitic effect of the measuring equipment itself is enough to skew the measurements.

Several methods have been developed to navigate around this problem and measure switching losses passively under realistic working conditions. They allow an accurate assessment of switching losses at different currents, voltages, and temperatures without requiring any modification to the switch cell itself. It becomes possible to accurately measure even fully integrated modules.

Direct switching loss measurement:

  • In switching cell measurement (classic double pulse) for GaN and SiC
  • Commutation loop current measurement
  • Low additional inductance of 300 pH
  • Bandwidth of 500 MHz
  • High resolution control signal
  • Up to 4 gate signals
  • Configuration script
  • Pulse and dead time resolution of 250 ps
  • Coil for measurement purposes
  • Calibrated up to 100 MHz
  • Low stray field due to toroid shape
  • Low HF losses due to litz wire
  • Pulse resistant up to 150 A because no magnetic material is used
  • U_DC = 600 V
  • I_L = 20 A
  • L = 7 uH
  • dU/dt = 70 V/ns --> 600 V in 8.5 ns !!!
  • dI/dt = 18 A/ns

Indirect switching loss measurement:

  • Measuring switching losses under real working conditions without commutation loop current measurement
  • This measurement method does not add parasitics to the switching cell and does not influence the switching behavior
  • Principle:
  • Measuring the input power with a high class power analyzer and subtract the known losses of the inductor
  • Measuring short period of time to reduce the thermal influence (100 ms)
  • Well known air core inductor with low losses
  • Very accurate PWM Unit
  • Forced air cooling of semiconductors and inductor
  • Features:
  • Separating turn-on and turn-off losses by different control modes
  • Zero Voltage switching to measure the switching-off losses
  • Hard switching mode for measuring switching-on and -off losses
  • System controlled by software
  • Software communicates with
  • Precision power meter
  • PWM signal timer
  • Oscilloscope
  • Power supply
  • High resolution control signal
  • Up to 4 gate signals
  • Pulse and dead time resolution up to 250 ps
  • Coil for measurement purpose
  • Calibrated up to 100 MHz
  • Low stray field due to toroid shape
  • Low HF losses due to litz wire
  • Pulse resistant up to 150 A because no magnetic material is used
  • Inductor losses can be determined precisely due to calculation and impedance measurement