Abstract
For determining the dynamic on -resistance $R_{{\rm dyn},{\rm on}}$ of a power transistor, the voltage and current waveforms have to be measured during the switching operation. The novel heterostructure wide-bandgap (e.g., AlGaN/GaN) transistors inherently suffer from the current collapse phenomenon, causing the dynamic on -resistance to be different from the static. Measuring voltage waveforms using an oscilloscope distorts the characteristics of an amplifier inside the oscilloscope when the range of the measurement channel is not set wide enough to measure both on -state and off -state voltage levels, resulting in failure to accurately measure the voltage waveforms. A novel voltage clamp circuit improving the accuracy of the transistor's on -state voltage measurement is presented. Unlike the traditional clamping circuit, the presented voltage clamp circuit does not introduce delay caused by $RC$ time constants, keeping the voltage waveform clear, even during state transitions of the device under test. The performance of the presented circuit is illustrated by measurements on a 2-MHz inverted buck converter.
Highlights
The reduction of losses in power converters is indisputably one of the most important issues in the field of power electronics
The presented voltage clamp circuit does not introduce delay caused by RC time constants keeping the voltage waveform clear, even during state transitions of the device under test (DUT)
The presented voltage clamp circuit is capable of measuring the on-resistance of a device while switching at high frequencies, and allowing one to determine its conduction loss
Summary
The reduction of losses in power converters is indisputably one of the most important issues in the field of power electronics. In recently developed GaN heterostructure semiconductor devices, this problem is even more pronounced because these devices exhibit a much lower on-resistance for the same blocking voltage than silicon devices, and can be downscaled with respect to traditional components, allowing them to switch faster [18]–[21] This means that for wide-bandgap devices an even higher measurement resolution is required and that measurements should be performed with faster circuitry. Conventional circuits partially solve this problem by clamping the off-state voltage to a lower value [22] They introduce problems such as voltage peaks, measurement offset and delays due to RC time constants. The presented voltage clamp circuit is capable of measuring the on-resistance of a device while switching at high frequencies, and allowing one to determine its conduction loss. The influence of temperature on the measurement accuracy is evaluated
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